The Pike Lake Pluton - A Layered Syenite Intrusion in Lanark County

The Pike Lake Pluton lies about 12 kilometres (8 miles) south of Perth between Pike Lake and Black Lake.  It falls mainly within North Burgess Township of Lanark County (now Burgess Ward of Tay Valley Township), and extends westward into North Crosby Township of Leeds County.

The Pike Lake Pluton is comprised of syenite and  has been dated at 1178 ±  3 Ma by Davidson and van Breemen  (2000), who placed it in the Frontenac terrane of the Central Metasedimentary belt of the Grenville Province.  

The pluton is shown on  the following geological map and described in   Jean Dugas' doctoral thesis, where it is identified as the Black Lake body.

Wilson, Morley E. and  Dugas, Jean,  1961,
Map 1089A, Geology, Perth, Lanark and Leeds Counties, Ontario, Geological Survey of Canada; Geology by Morley E. Wilson, 1930 and Jean Dugas, 1949; Descriptive notes by Jean Dugas.
https://doi.org/10.4095/107951

Dugas, Jean, 1952,
 Geology of the Perth map area, Lanark and Leeds Counties, Ontario; Ph. D., McGill, 189 pages, four  maps.     Map 1089A replicates a map that is part of the  thesis.
http://www.collectionscanada.gc.ca/obj/thesescanada/vol2/QMM/TC-QMM-124004.pdf
http://digitool.library.mcgill.ca/thesisfile124004.pdf
  
Below is an extract from Map 1089A  showing the Pike Lake  pluton.

The Bedding (Igneous Layering)

Worth noting on Map 1089A is that bedding (igneous layering)  is shown for at least 22 locations within the boundaries of the pluton, and that at 14 locations the map shows foliation.   Further, in the text of his thesis Dugas (1952) remarked on the good bedding within the syenite body and included a spectacular photo of bedding in the syenite body (his photo number  54 at page 159 of his thesis).   Dugas places the outcrop shown in  photo  number  54 in Lot 24, Concession VI of North Burgess township.   (Locating that outcrop is problematic as his Black Lake syenite body (the Pike Lake pluton) does not appear to outcrop in Lot 24 of Concession VI.)

One interesting feature within the Pike Lake Pluton, that is shown on the above extract from Map 1089A, is a thin lens of pyroxenite syenite along the Eastern margin (close to Black Lake)  that is parallel to the bedding and extends over a length of at least one and a half miles (2.4 kilometers).  The lens appears to be about 1/16 of a mile (100 meters) thick.  It would be interesting to determine whether this is layering within the syenite body, or a separate intrusion.

The Syenite

Jean Dugas (1952) identified four main syenite bodies within his map area: the McGowan-Lanark body, the Bathurst body, the Crosby body and the Black Lake body.   What recent authors call the Pike Lake pluton, Jean Dugas called the Black Lake body. 

Jean Dugas summarized the common characteristics of the four main syenite bodies as follows (pages 52-53):

“1. The rock is commonly pink though it may grade to grey or brown where magnetite is most abundant. The brown coloring is probably caused by staining of the feldspars by iron hydroxide.
2. The rock varies in grain size from 1 mm. to 5 mm. and may be porphyritic.
3. The predominant mafic minerals are biotite and hornblende (near hastingsite in composition), pyroxene being only minor in amount.
4. The magnetite-ilmenite content is high, though not uniformly distributed. All syenite bodies give strong magnetic anomalies, though sections are poorly magnetic.
5. Accessory minerals are mainly apatite and sphene, the latter commonly forming a rim around magnetite crystals.  Sphene is probably secondary after ilmenite (cf'. photo no. 71 p. 54).
6. The feldspars are microcline and oligoclase (Ab. 85).
7. The foliation is prominent near the margins of the body.
8.  Migmatitic complex of' granite and syenite is common along the margins of these larger syenite masses. “

He also comments specifically on the Black Lake Body:

At pages 51-52,
"Another lens-shaped body (Black Lake body) lies between Pike Lake and Black Lake. This body has a maximum width of slightly more than a mile and extends for more than four miles."

At pages 59 - 60
“Black Lake body
This is one of the most interesting of the syenite bodies. The rock at the center of the body, though variable in grain size and color, is typically brownish, medium grained and massive. Away from the center of the body, the syenite has similar composition but is very well banded   (ct. photo no. 54 p. 159).  Further from the center the rocks are syenite-granite migmatite and on the outer edges are garnet gneiss. Good exposures of the latter occur on the shore of Pike Lake. Reference to this body is made in subsequent chapters."
           
At pages 152, 153
“Magnetic Data
Glancing at the geological map and the air survey magnetic contour intervals, there can be no doubt that all major magnetic anomalies are caused by syenite or quartz syenite bodies. ... [T]he Black Lake body is probably the best example of a sharp magnetic anomaly, though readings do not exceed 1,700 gammas. Contacts could have been traced fairly accurately from the magnetic contours alone.”

At pages 158, 161
“No absolute evidence of the magmatic origin of the syenites, granites and diorites can be given. The beat example of these features is within the Black Lake syenite body ( cf. figure p. 160). The center of this body is massive and around the massive rocks, without sharp contact, very well bedded  rocks (cf. photo no. 54, p. 159) have obviously an igneous syenite composition. The rock then grades to a migmatitic complex of syenite-granite and, on the shore of Pike Lake, to a typical biotite-garnet gneiss.”
   

OGS Re-mapping the Perth Sheet

In my blog posting from last December I mentioned that Dr. Easton of the Ontario Geological Survey is currently remapping the Perth Sheet.  Within the Perth map area Dr. Easton (2015, 2016a) has divided the Frontenac terrane  into 3 subdomains:  the western, central and eastern subdomains.   From the text of his reports it appears that he places the Pike Lake Pluton within his western subdomain, commenting (2015, at page 18-6): “Frontenac suite intrusions in the western subdomain consist of pre- to syntectonic (e.g., Pike Lake pluton, 1178±4 Ma), syntectonic (e.g., Bennett Bay pluton, 1164±2 Ma) and posttectonic (e.g., North Cosby pluton, 1157±3 Ma) intrusions (all ages from Davidson and van Breemen 2000). This relative age range is also observed in the smaller Frontenac suite intrusions. Older intrusions, especially the smaller bodies, appear to be more quartz rich (quartz syenite, quartz syenite) than the younger intrusions (syenite, monzonite).”    He also notes that “The western subdomain consists of both felsic and mafic Frontenac suite intrusions that are rimmed by migmatitic, compositionally varied, quartzofeldspathic gneisses that are commonly cut by smaller irregular bodies and sills of Frontenac suite intrusive rocks. It is not clear if these smaller intrusive bodies are simply sheet-like injections of magma emplaced during deformation, or if they represent cupolas or roof-pendants of a larger intrusive body at depth.”    His final report should be worth reading.

Christopher Brett
Perth

References and Suggested Reading

Davidson, A. and van Breemen, O., 2000
Age and extent of the Frontenac plutonic suite in the Central metasedimentary belt, Grenville Province, southeastern Ontario; Geological Survey of Canada, Current Research 2000-F4; Radiogenic Age and Isotopic Studies: Report 13; 15 pages;
https://books.google.ca/books?isbn=0660182300
publications.gc.ca/collections/Collection-R/GSC-CGC/M44-2000/M44-2000-F4E.pdf

Easton, R. M.,  2015
Project Unit 15-014. Precambrian and Paleozoic Geology of the Perth Area, Grenville Province; in Summary of Field Work and Other Activities, 2015. Ontario Geological Survey, OFR 6313
at pages 18-1 to 18- 13
http://www.mndm.gov.on.ca/en/news/mines-and-minerals/summary-field-work-and-other-activities-2015  
              
Easton, R.M.,  2016a.
Precambrian and Paleozoic geology of the Perth area, Grenville Province; in Summary of Field Work and Other Activities, 2016, Ontario Geological Survey, Open File Report 6323, p.17-1 to 17-13.

Easton, R.M.,  2016b.
Metasomatism, syenite magmatism and rare earth element and related metallic mineralization in Bancroft and Frontenac terranes: A preliminary deposit model; in Summary of Field Work and Other Activities, 2016, Ontario Geological Survey, Open File Report 6323, p.18-1 to 18-9.

Both of Dr. Easton's 2016  reports can be downloaded from:
http://www.mndm.gov.on.ca/en/news/mines-and-minerals/summary-field-work-and-other-activities-2016

Outcrops of Orbicular Granite in Lanark County, Ontario

“Orbicular granite (also known as orbicular rock or orbiculite) is an uncommon plutonic rock type which is usually granitic in composition. These rocks have a unique appearance due to orbicules - concentrically layered, spheroidal structures, probably formed through nucleation around a grain in a cooling magma chamber. Almost one third of known orbicular rock occurrences are from Finland. The occurrences are usually very small.”
https://en.wikipedia.org/wiki/Orbicular_granite

There is a tremendous amount written on orbicular rocks.  Kennan and  Lorenc (2008) provide a discussion of the early discoveries of orbicular rocks.  They mention that “In 1802, Leopold von Buch described some outcrops of orbicular granite in the Karkonosze granite, Lower Silesia, Poland. ...  The Silesian discovery predates that of the well-known orbicular diorite (Napoleonite) in outcrop on Corsica and, thus, may be the first ever record of this distinctive rock type in its geological context.”

David Levenson (1989) provides the following summary: “Orbicular rocks are nonsedimentary rocks that contain concentric shells of different texture and/or mineralogy about a central core. Occurrences have been described from every continent, and orbicules have been found in ultramafic to felsic, igneous, and metamorphic rocks. Host rocks are fine- to coarse-grained, and include dykes, sills, stocks, batholiths, lavas, gneisses, schists, and migmatites. Orbicular facies are generally local, less than several hundred meters in greatest dimension. ... Orbicules range from <3 cm to >30 cm in diameter. Shells number from one to more than twenty, and may be spaced irregularly or in geometrical progression.”

Numerous theories have been advanced to explain the formation of orbicular rocks.  Sage (1987), who noted that they occur in magmatic, metamorphic and migmatic terrains and have various compositions, provides a list of eight proposals from Levenson (1966) and mentions a ninth advanced by Elliston (1984).  The nine theories are: liquid immiscibility; fluctuations of a melt about a eutectic or eutectoid due to variations in pressure and temperature; reactions between magmas and xenoliths; xenoliths moving through parts of magma of different compositions; crystallization of concentric envelopes of contrasting composition in a highly viscous magma that retards viscous diffusion; excessive crystallization of one component around a nucleus, followed by excessive crystallization of a second component, as a result of  alternating supersaturation;  rhythmic supersaturation and crystallization about centres in a magma in a manner analogous to Leisegang ring formation;  layers built up on a previously formed nucleus in a silicate melt, with diffusion of material, and crystallization later than the formation of the orbicular structure.   More recent theories involve nucleation in small pockets of H2O-rich superheated silicate melt, with the orbicule shell structures crystallizing and growing from supercooled boundary layers within the  magma  (Owen, 1991; Ort, 1992; Grosse et al, 2010; Smillie and Turnbull,  2014).

Lanark's Outcrops

What is not widely known is that Lanark County is home to at least three occurrences of orbicular granite, which are mentioned in the notes to the following map and described in the following doctoral thesis.

Wilson, Morley E. and  Dugas, Jean,  1961,
Map 1089A, Geology, Perth, Lanark and Leeds Counties, Ontario, Geological Survey of Canada; Geology by Morley E. Wilson, 1930 and Jean Dugas, 1949; Descriptive notes by Jean Dugas.
https://doi.org/10.4095/107951

Dugas, Jean, 1952,
 Geology of the Perth map area, Lanark and Leeds Counties, Ontario; Ph. D., McGill, 189 pages, four  maps.    
http://www.collectionscanada.gc.ca/obj/thesescanada/vol2/QMM/TC-QMM-124004.pdf
http://digitool.library.mcgill.ca/thesisfile124004.pdf

Surprisingly, the outcrops of orbicular granite are not mentioned in the following paper:

Dugas, Jean, 1950,
Perth map-area Lanark and Leeds Counties Ontario; Geological Survey of Canada, Paper no. 50-29, 1950; 22 pages (1 sheet), https://doi.org/10.4095/101399

In the descriptive notes to Map 1089A,  Jean Dugas mentions:

“Small bodies of granite are exposed in various parts of the map-area.  Among these, and too small to be mapped separately, are exposures of an ‘orbicular’ granite, composed of granite ovoids and basic rims.  These can be best observed on lot 20, con. 1, North Crosby township.”

I have to admit I’ve known about that reference for over five years and have not yet made the time to visit the occurrence, largely because the two options are (a) to ford a stream and walk across a swamp, or (b) launch my canoe at the far end of Pike Lake and paddle to the outcrop.

Jean Dugas (1952) discusses the occurrences of orbicular granite at pages 67-73 of his doctoral thesis. He mentions three occurrences:
- on lot 20, concession I of North Crosby township, on the southwest end of Pike Lake;
- on lot 16, concession VIII of North Burgess township (to the northeast of Pike Lake);
- on lot 18, concession III of South Sherbrooke township, north of Christie Lake.   
Outcrops of granite on those lots and concessions in North Crosby township and North Burgess township are shown on Map 1089A.   On the following extract from Map 1089A I've shown the three locations by florescent pink boxes.

At page 68 of his thesis Jean Dugas includes four photographs of the outcrops: three photographs of the outcrop  on lot 20, concession I of North Crosby township; one of the outcrop on lot 16, concession VIII of North Burgess township; but none of the outcrop on lot 18, concession III of South Sherbrooke township.  At page 70 he includes photographs of thin sections from the outcrop in North Crosby township.
   
Jean Dugas (1952)  mentions (at pages 67, 69; 72-73) that the outcrop near the southwest end of Pike Lake “can be observed very plainly. A scarp on the east side shows a good exposure of rock. The band may reach 20 feet in width. It seems to be in the form of a lens: at a distance of 1000 feet from the best exposure, it is only about two feet wide. It is composed of rounded pieces of granite, in places longitudinally arranged along the strike and dip and surrounded by a thin, very basic rim of amphibolite composition. The size of the granite pieces ranges from one inch to more than one foot and the rim is one half to one inch wide. The shape of the granite and the interstitial material approaches that of pillow structure (cf. photo no. 13, p. 68). The granite is composed of pink microcline and quartz with a few pyroxene crystals penetrating from the basic rim (cf. photo no. 17, p. 70). The rim itself is composed of augite and oligoclase for the most part.
...
The study of the Perth orbicular granite is particularly difficult as there is no recognizable matrix and no non-orbicular granite in adjacent areas from which the rock may have derived. However, it is remarkable that the center of orbicules is free from ferric minerals and there is sharp increase of these towards the rim. No microcline is observed in the rim and the composition is esboitic (oligoclasic). There is also evidence of replacement between sodic feldspar and microcline (cf. photo no. 18, p. 70).”

In his thesis Jean Dugas also describes a leopard pegmatite from Lot 12, concession V of North Burgess township and includes a photograph of the outcrop at page 79.   He mentions “At the Silver Queen mine, a pegmatite shows locally a faint sinuous system of black stringers composed of ferromagnesian minerals.  This type of pegmatite has been called ‘leopard pegmatite’ (c.f'. photo no. 2l, p. 79), and is probably of orbicular nature.”

The best references to orbicular rocks that I have been able to find are the following French language GEOWIKI articles: 

Les roches orbiculaires
http://www.geowiki.fr/index.php?title=Les_roches_orbiculaires

Les types de roches orbiculaires
http://www.geowiki.fr/index.php?title=Les_types_de_roches_orbiculaires

Liste des occurrences dans le monde
http://www.geowiki.fr/index.php?title=Liste_des_occurrences_dans_le_monde    

Interestingly that list of worldwide occurrences of orbicular rocks does not include the outcrops in Lanark County.

Also worth a look are the following videos on the Granito Orbicular of Chile: 
https://www.youtube.com/watch?v=j_yx3sTz3co    5:08
https://www.youtube.com/watch?v=HkfIiGNl41A    1:33
https://www.youtube.com/watch?v=yaMEfVZMvPc      1:02

Christopher Brett
Perth, Ontario


References and A Reading List on Orbicular Rocks:

Adams, Frank. D., 1897
 Nodular granite from Pine Lake, Ontario;  Geological  Society  of  America
Bulletin,  vol. ix, pp. 163-172; reprinted as McGill University, Papers from the Department of Geology, No. 8. ,  https://archive.org/details/cihm_02281       

Affholter, Kathleen A. and Lambert,  E. E., 1982
Newly described occurrences of orbicular rock in Precambrian granite, Sandia and Zuni Mountains, New Mexico; in  Wells, S. G.; Grambling, J. A.; Callender, J. F.; [eds.] New Mexico Geological Society Guidebook, 33rd Field Conference, Albuquerque Country II, 1982, pages 225-232
https://nmgs.nmt.edu/publications/guidebooks/downloads/33/33_p0225_p0232.pdf

Blake, William P., 1904
Origin of Orbicular and Concretionary Structures, Transactions of the American Institute of Mining Engineers, vol. XXXVI,  677- 682
library.aimehq.org ...bulletin of the AIME 1905 1-6-047.pdf

Bräunlich, Matthias
Orbiculite - eine Auswahl:
http://www.kristallin.de/orbiculite/kugelgesteine2.htm#Anker1
Orbicular Rocks
http://www.kristallin.de/orbiculite/orbicular_rocks1.htm

Elliston, John N. 1984,
Orbicules: An indication of the crystallisation of hydrosilicates, I;  Earth-Science Reviews, Volume 20, Issue 4, August 1984, Pages 265-344
https://doi.org/10.1016/0012-8252(84)90021-7
   
Enz, Robert D., Albert M. Kudo, and Douglas G. Brookins; 1979
Igneous origin of the orbicular rocks of the Sandia Mountains, New Mexico, Geological Society of America Bulletin, February, 1979, v. 90, p. 138-140
https://doi.org/10.1130/GSAB-P2-90-349

Grosse, Pablo; Toselli, Alejandro J.; and  Rossi, Juana N., 2010
Petrology and geochemistry of the orbicular granitoid of Sierra de Velasco (NW Argentina) and implications for the origin of orbicular rocks; Geological Magazine, vol. 147,  no. 3, 451-468
DOI: 10.1017/S0016756809990707
   
Hitchcock, Edward; Edward Hitchcock, jr., Albert D. Hager, Charles H. Hitchcock. 1861
Report on the Geology of Vermont: descriptive, theoretical, economical, and scenographical.  Vol. 2, pp. 563, 564, 721, (the nodular granite of Craftsbury; the Craftsbury pudding granite)
https://babel.hathitrust.org/cgi/pt?id=mdp.39015086763169;view=1up;seq=20

Hudec, P. P.,  1964
Geology of the Big Trout Lake Area District of Kenora (Patricia Portion); Ontario Department of Mines, Geological Report No. 23 “A rather peculiar orbicular volcanic rock has been observed ... [which] consists of very fine-grained siliceous and chloritic concentric features, with fine quartz  in the centre, a ring of fine chlorite around it, surrounded by a ring of chlorite of different composition.   The large rings  (1/2  to l  inch   in   diam.) have small orbicular features within them.   The rock is dark, hard, and brittle.”

Kemp, J. F., 1894
An orbicular Granite from Quonochontogue, Beach, Rhode Island, Transactions of the New York Academy of Sciences, Volumes 13-14, pages 140 - 144
https://books.google.ca/books?id=AcoAAAAAYAAJ

Kennan, Pádhraig S. And Lorenc, Marek W.,  2008
Orbicular granite near Jelenia Góra in southwestern Poland: the first outcrops; 
Mineralogia, Volume 39, Issue 3-4, pp. 79-85
Open Access: DOI: https://doi.org/10.2478/v10002-008-0006-4

Kessler, H.S. and Hamilton, W.E., 1904      
The Orbicular Gabbro of Dehesa, California; American Geologist, Vol. Xxxiv, No. 3, 123-140 with five plates 
https://archive.org/stream/panamericangeolo341904desm#page/n165/mode/2up   

Lahti, S. (Editor), 2006
Orbicular Rocks in Finland 2005, with contributions by P. Raivio and I. Laitakari.
Espoo (Geological Survey of Finland) ISBN: 951-690-911-6. , 177 pages

Lawson, Andrew C., 1904
The Orbicular Gabbro of Dehesa, San Diego County, California;   Volume 3, Issue 17 of University of California publications: Bulletin of the Department of Geology; pp 383-396
https://archive.org/stream/bulletinofde319021904univ#page/n549/mode/2up

Levenson,  David  J., 1966,
Orbicular  rocks:  A  review:  Geological  Society  of  America Bulletin, v. 77, p. 409- 426
http://dx.doi.org/10.1130/0016-7606(1966)77[409:ORAR]2.0.CO;2
   
Levenson,  David J. (1989)
Orbicular Rocks; in Petrology, Encyclopedia of Earth Science, pp 415-416, Springer
link.springer.com/10.1007/0-387-30845-8_168
DOI   10.1007/0-387-30845-8_168

Ort, Michael H., 1992
Orbicular volcanic rocks of Cerro Panizos: Their origin and implications for orb formation;
Geological Society of America Bulletin, August 1992, vol. 104 no. 8 1048-1058
DOI: 10.1130/0016-7606(1992)104<1048:OVROCP>2.3.CO;2

Owen,  J. Victor, 1991
Significance of epidote in orbicular diorite from the Grenville Front zone, eastern Labrador; Mineralogical Magazine, June 1991, Vol. 55, pp. 173-18I
http://www.minersoc.org/pages/Archive-MM/Volume_55/55-379-173.pdf

Sage, R. P., 1987
Geology of Carbonatite-Alkalic Rock Complexes in Ontario: the Prairie Lake Carbonatite Complex, District of Thunder Bay; Ontario Geological Survey Study 46, 91 pages at 20-22
http://www.geologyontario.mndmf.gov.on.ca/mndmfiles/pub/data/imaging/S046/S046.pdf

Smillie, Robert W. and Turnbull, Rose E,  2014
Field and petrographical insight into the formation of orbicular granitoids from the Bonney Pluton, southern Victoria Land, Antarctica; Geological Magazine,   Volume 151, Issue 3,  May 2014, pp. 534-549           DOI: https://doi.org/10.1017/S0016756813000484

Watson, Thomas Leonard, 1904
Orbicular Gabbro-Diorite from Davie County, North Carolina; The Journal of Geology, Volume 12, pp 294 - 303    https://archive.org/details/jstor-30055824

Zihkel, Ferdinand, 1894
Lehrbuch der Petrographie, 2d ed., vol. 2, pages 50, 51-
https://archive.org/stream/lehrbuchderpetr01zirkgoog#page/n59/mode/2up

Why has hardly anyone referred to core from the GSC’s Borehole Geophysics Test Area at Bell’s Corners, Ottawa, when the core contains a 50 cm thick shale layer in the Nepean Formation and the core straddles the boundary between the Nepean Formation and the overlying March Formation?

I have to admit that I cannot answer that question and that I’m writing a blog posting on the topic in the hopes that someone will be able to provide an answer.

Below I’ll set out what was reported in the literature and will discuss why the core should be looked at with fresh eyes.

In 1981 and 1984 the Geological Survey of Canada drilled six vertical 75 mm (2.95 inch) holes at the Borehole Geophysics Test Area on the grounds of Natural Resources Canada’s  CANMET Research Complex located at Bell’s Corners, Ottawa (Bernius, 1981; Killean, 1986; Bernius, 1996; Mwenifumbo et al., 2005).   Four of the holes are spaced along a 100 m line (at intervals of 10m, 20m and 70 m), while the other two were positioned to form two equilateral triangles with sides of 30 m and 100 m.  The three deepest holes were drilled to 300 m.  The boreholes are used to calibrate instruments for borehole geophysical measurements such as porosity, resistivity, etc.

Bernius (1981, 1996)  reported on the core.    The drill holes intersected about 65 m of Paleozoic rocks that dip at a low angle and thicken slightly to the north-northwest, underlain by Precambrian igneous and metamorphic rocks.   The core revealed (progressing down the holes):

Paleozoic
- 11 to 16 metres of Oxford Formation grey to reddish brown, sandy domomite;
- 4 metres of March Formation comprised of a massive quartz arenite on the top and a light-grey coloured dolomitic sandstone at the bottom
- Nepean Formation comprised of (still progressing down the holes):
  - 16 metres of pure, well sorted, massive, white sandstone
  - a 50 cm layer of reddish-brown shale
  -  27 metres comprised of a sequence of cross-bedded sandstones with fifteen bioturbate layers that range in thickness from 2 cm to 10 cm and alternate with the cross-bedding, with zones of vertical worms holes of the species skolithos, Diplocraterion and Arenicolites
  - a thin 5 cm layer of quartz-feldspar orthoconglomerate
Precambrian
- a 15 - 17 metre highly altered/weathered zone, a saprolite layer, in the Precambrian rocks
- syenites, granites and gneisses

Bernius (1996) mentions that the upper contact of the Nepean formation with the March Formation is a disconformity and that there is a sharp unconformity between the Paleozoic sequence and the Precambrian rocks.

The Borehole Geophysics Test Area is about a kilometer south of what is (or was) arguably a reference section for the Nepean Formation sandstone of the Potsdam Group that is found along highway 417 in Kanata (Greggs  and Bond, 1972).  Further, that section  has been used by a number of authors (Greggs and Bond, 1972, 1977; Bond and Greggs, 1973;  Brand and Rust, 1977a, b; Dix et al., 2004; Sanford and Arnott, 2010; Lowe et al., 2017 ) to try to settle the boundary between the Nepean formation and the overlying March formation.   An interesting  question is “Why has no one looked at the core from the Borehole Geophysics Test Area  to help resolve where to place the boundary between the Nepean Formation and the March Formation?”   (Other than perhaps the obvious answer that it was overlooked.)

A second issue is what to make of the 50 cm thick shale layer that Bernius (1996) reports in the Nepean Formation.   The shale layer is interesting because  I can find no reference to anyone else reporting a shale layer in the Nepean Formation of Ontario.  (Dolostone, mudstone and siltstone are reported in the Nepean  Formation, but no shale.)    I had initially wondered if  perhaps the reference to 50 cm should be perhaps 5cm, but note that later in the report, when discussing the geophysical logs for the Nepean Formation, Bernius (1996)  mentions that “From 36.8 m to 37.4 m there is a distinctive impure shaley layer.  The increase in the potassium log in this layer is due to the clay minerals, while the electrical log responses... also indicate the presence of more conductive materials....”

It is possible that the shale layer marks the boundary of the Nepean with the March (Theresa).   I make that suggestion because Bernius (1996) states  that the 50 cm layer of reddish-brown shale separates  two units of the Nepean Formation, a lower bioturbated and cross-bedded unit, and an upper, very pure , well sorted, white sandstone; and Bernius correlated his lower bioturbated layer with Greggs and Bonds’ upper bioturbated section which they placed just below the boundary the Nepean and the March (Theresa).     Bernius noted  that the boreholes are a kilometer south of the road cut on Highway 417 that Greggs and Bond  suggested for the principal reference section for the Nepean; but failed to consider that the shale could be the boundary between the Nepean (Keeseville) and the March (Theresa), and that his sorted, white sandstone could be part of the March.   It is also possible that all of Bernius’ sandstone is March formation sandstone.
  
Bernius (1981) and Bernius (1996) have  barely been mentioned.  Williams (1991) cites Bernius (1981) in three locations to refer to the 17 m alteration zone at the top of the Precambrian, for Bernius’ measured thickness for the Nepean at the CANMET complex, and for the thickness of the March Formation.  Mwenifumbo et al. (2005)  direct one to Bernius (1996)  for a discussion of the geology of the area and core.  Pilkington and Todoeschuck (1990) cite Bernius (1981) as the source for their cryptic summary of the geology.

Christopher Brett
Perth, Ontario

Addendum, November 14, 2021:                      

In a recent paper released on September 13, 2021  Crow et al. (2021) provided new geophysical data from the drill holes at the GSC’s Borehole Geophysics Test Site.  They also re-logged the drill core.  Their description of the rocks differs slightly from Benius’ description. For example, they have adopted  more current names for the formations, don’t mention the layer of reddish brown shale, and assign more rock to the Theresa (formerly the March) Formation, and  less rock to the Beauharnois (formerly lower Oxford) Formation.  This is their description of the Paleozoic rocks:

“Keeseville (Nepean) Formation (core depths 20.45 – 64.30m)
The contact with the basement occurs at a 20cm thick quartz conglomerate with some brownish limonitic layers (Bernius, 1996). A 5.2m-long interval of white quartz sandstone overlies the conglomerate. Overlying this is a sandstone sequence characterized by alternating bioturbated and cross-bedded sandstone, both with variable amounts of hematite (visible iron staining), glauconite and limonite. There are 23 bioturbated layers identified, ranging in thickness from 5 to 83cm. Burrows are frequently seen in this interval. The upper 16m of the Keeseville Formation is characterized by massive, white quartz arenite with some dark laminae and irregular layers.

Theresa and Beauharnois Formations (core depths 5.30 (top of core) – 20.45m)
The Theresa Formation is composed of interbedded sandy calcareous dolostone and calcareous
sandstone. The base of the formation contains a distinct dark grey layer of uranium-bearing and
chalcopyrite-rich pyrobitumen (Charbonneau et al., 1975; Bernius, 1996) also known as thucolite (see Hoekstra and Fuchs, 1960). The core transitions upward into a grey, fine to medium crystalline dolostone, containing a few very thin interbeds of fine grained quartz sandstone.  Calcite-filled cavities are observed in core. The upper several metres of core are broken and fractured, with visible weathering along vertical fracture surfaces. The transitional nature of the Theresa Formation upward into the Beauharnois Formation leaves assigning the contact between the two open for re-examination. The local thickness of the Theresa Formation has been interpreted to be about 10m, suggesting that the upper few metres of core could be Beauharnois Fm.”

Crow, H L; Brewer, K D; Cartwright, T J; Gaines, S; Heagle, D; Pugin, A J -M; Russell, H A J
2021    New core and downhole geophysical data sets from the Bells Corners Borehole Calibration Facility Ottawa, Ontario.  Geological Survey of Canada, Open File 8811, 2021, 36 pages, https://doi.org/10.4095/328837      Released:   2021 09 14
 
See also my two blog postings from October, 2021 entitled Abandoned Nepean Sandstone Quarries and Outcrops in the Greenspace West of Bells Corners -

References

Bernius, G. R., 1981,
Boreholes Near Ottawa for the Development and Testing of Borehole Logging Equipment - A preliminary Report GSC Paper 81-1C, p. 51-53
  
Bernius, G. R., 1996,
Borehole Geophysical Logs from the GSC Borehole Geophysics test site at Bell’s Corners, Nepean, Ontario, GSC Open File 3157, 38 pages, doi:10.4095/207617
(pdf  6427 KB)

Bond, I.J., and Greggs, R.G. 1973.
 Revision of the March Formation (Tremadocian) in southeastern Ontario. Canadian Journal of Earth Sciences, 10 : 1140–1155.    10.1139/e73-098

Brand, U., and Rust, B.R.,  1977a
The age and upper boundary of the Nepean formation in its type section area near Ottawa, Ontario. Canadian Journal of Earth Sciences, 14: 2002–2006.
www.nrcresearchpress.com/doi/abs/10.1139/e77-171 #.WR-TQbiN0r0

Brand, U., and Rust, B.R., 1977b
 The age and upper boundary of the Nepean formation in its type section area near Ottawa, Ontario: Reply. Canadian Journal of Earth Sciences, 14: 2671–2673.   10.1139/e77-233

Dix, George R.,  Salad Hersi, Osman, and  Nowlan, Godfrey S.,  2004
The Potsdam-Beekmantown Group boundary, Nepean Formation type section (Ottawa, Ontario): a cryptic sequence boundary, not a conformable transition, Canadian Journal of Earth Sciences, 2004, 41(8): 897-902,  http://www.nrcresearchpress.com/doi/pdf/10.1139/e04-040

Greggs, R. G.  and Bond, I. J., 1972
A principal reference section proposed for the Nepean  Formation of probable Tremadocian age near Ottawa, Ontario. Canadian Journal of Earth Sciences, 9, pp. 933-941.         www.nrcresearchpress.com/doi/abs/10.1139/e72-078

Greggs, R. G.  and Bond, I. J., 1977
The age and upper boundary of the Nepean formation in its type section area near Ottawa, Ontario: Discussion. Canadian Journal of Earth Sciences, 14: 2669–2671. 10.1139/e77-232

Killean, P.G., 1986,
A System of Deep Test Holes and Calibration Facilities for Developing and Testing New Borehole Geophysical Techniques, GSC Paper 85-27, p. 29-46; (pdf   54803 KB); doi:10.4095/123600;  in, Borehole geophysics for mining and geotechnical applications; Killeen, P G (ed.); Geological Survey of Canada, Paper 85-27, 1986;
      
Lowe, David G.,, Arnott,R.W.C.,  Nowlan, Godfrey S.,  McCracken, A.D.,  2017
Lithostratigraphic and allostratigraphic framework of the Cambrian–Ordovician Potsdam Group and correlations across Early Paleozoic southern Laurentia; Canadian Journal of Earth Sciences, Published on the web 6 February 2017,    doi: 10.1139/cjes-2016-0151

Mwenifumbo, C.J., Elliott, B.E., Hyatt, W.G., Bernius, G.R., 2005
Bells Corners calibration facilities for downhole and surface geophysical equipment. Geological Survey of Canada, Open File 4838, 18 p. http://geochem.nrcan.gc.ca/cdogs/content/pub/pub10463_e.htm
  
Pilkington, M. And Todoeschuck, J.P., 1990
Stochastic inversion and scaling geology; Geophys. J. Int. 102, 205-217

Sanford, B.V. and Arnott, R.W.C.,  2010
Stratigraphic and structural framework of the Potsdam Group in eastern Ontario, western Quebec, and northern New York State.  Geological Survey of Canada, Bulletin 597, 85 pages
publications.gc.ca/collections/collection_2010 /nrcan/M42-597

Williams, D.A., 1991
Paleozoic Geology of the Ottawa-St. Lawrence Lowland, Southern Ontario; Ontario Geological Survey, Open File Report 5770, 292p, at 29,46 and 56

Andrew’s Outcrops

Andrew is one of the many polite teenagers that Lanark County produces by the bushel load.   He also has a keen interest in geology.  This past weekend I took the opportunity to visit outcrops that Andrew had been telling me about.  

Most of the outcrops that Andrew showed me consist of flat lying sandstone exhibiting paired vertical burrows on the top surface.   I expect that everyone would identify this sandstone as a shallow marine facies of the Nepean (upper Keeseville) Formation of the Potsdam Group.   Below are photographs of the top surfaces of  two such sandstone outcrops, each showing paired vertical burrowing.

One outcrop stood out as being particularly impressive and is likely worth a second visit.  Below are photographs of this outcrop.This outcrop can be divided into three parts, with at least two visible unconformities (separating layers 1 and 2; and separating layers 2 from 3).  Starting from the base you notice:
1.)  at least 30 vertical feet of a silicious quartz cobble conglomerate; 
2.)  followed by a foot of sandstone with layers of quartz pebbles and a pitted layer (that may represent eroded evaporite minerals?);
3.)  with a top layer showing bedded  sandstone cut by vertical burrows, some of which extend down into the middle layer (perhaps evidencing the transgression of Cambrian/Ordovician seas and the reworking of fluvial sandstone?).

The two lower layers are of continental/fluvial origin, while the upper layer is of shallow marine origin.  

The first three photographs show the basal quartz cobble conglomerate.   The fourth photograph shows two unconformities, with the basal quartz cobble conglomerate at the bottom of the photo.   The fifth photo shows vertical burrowing and an uncomformity.  The sixth photo shows vertical burrowing in the top layer (shallow marine sandstone), overlying what appears to be two fluvial events: a pebble layer, over  sandstone, over a pebble layer, over sandstone (with the pebble layers possibly being lag deposits formed by aeolian deflation?).

           
I expect that everyone would assign the top burrowed bed to a shallow marine facies of  the Nepean (upper Keeseville) Formation.    Most people would likely  assign the quartz cobble conglomerate bed  to the Covey Hill (Ausable) Formation of the Cambrian/Ordovician Potsdam Group, with some assigning it a Precambrian age.   The middle bed is likely a fluvial facies of the Nepean (lower Keeseville) formation.

Andrew also showed me a mica mine in the Precambrian rocks and a lichen covered, deeply fractured, sandstone ridge that lies on an adjoining property

The photographed outcrops fall within Lot 7 of Concession VIII in North Burgess Township (now Burgess Ward of Tay Valley Township), about four miles (6.5 kilometers) south of Perth, and west of the intersection of Stanley Road with the road to McLaren Lake.   The lichen covered sandstone ridge can be found east of the road to McLaren Lake, on Lot 8 of Concession VIII.

If you were one of the original settlers who had been granted the land upon which Andrew’s parents have their house, or granted one of the adjoining lots, I suspect you’d have complained about the lack of soil.  If you have an interest in geology, which Andrew has, you’d be pleased to be living there.

Christopher Brett
Perth, Ontario   

Suggested Reading:
David G. Lowe, R.W.C. Arnott, Godfrey S. Nowlan, A.D. McCracken, 2017
Lithostratigraphic and allostratigraphic framework of the Cambrian–Ordovician Potsdam Group and correlations across Early Paleozoic southern Laurentia; Canadian Journal of Earth Sciences, Published on the web 6 February 2017,    doi: 10.1139/cjes-2016-0151

The Cylindrical Structures in Lanark County reported in Jean Dugas’ 1952 Doctoral Thesis

In my  August 27, 2015 blog posting I mentioned that Jean Dugas,in the notes to geological  Map 1089A, reported that cylindrical or conical structures in sandstone can be found in North Elmsley Township,  Lanark County.   He commented:

“Peculiar bands showing cylindrical or conical structures noted in the Nepean formation, and best observed on lot 24, Con. VI, North Elmsley tp., are the same composition as the surrounding sandstone , but cut sharply across the beds and are themselves bedded parallel with the walls of the structures.  They are probably formed by slumping of the sand due to water action.”

Morley E. Wilson and Jean Dugas, 1961,
Map 1089A, Geology, Perth, Lanark and Leeds Counties, Ontario, Geological Survey of Canada; Geology by Morley E. Wilson, 1930 and Jean Dugas, 1949; Descriptive notes by Jean Dugas.
                 
In my August 27, 2015 blog posting I also mentioned that I had not been able to find  Dugas’ occurrence on Lot 24 or his thesis.

I  recently located and read Jean Dugas’ doctoral thesis:

Dugas, Jean, 1952,
 Geology of the Perth map area, Lanark and Leeds Counties, Ontario; Ph. D., McGill, 189 pages, four  maps.          

In his thesis he includes five clear  photographs of the conical and cylindrical structures, and good written descriptions of the structures, together with a review of the leading papers discussing theories for their origin.  He concludes that his structures, because of their conical shape, were formed by slumping, and suggests that “as most of the structures are underlain by [crystalline] limestone and it is common to find solution cavities in the [crystalline] limestone” the slumping was likely into cavities in the limestone.

Interestingly, while the the captions to his photographs place the structures on lot 24, the  text of Jean Dugas’ thesis mentions that the structures are found on lot 23.   Both the text and the captions place the structures in concession VI.  In the text of his thesis he comments (at page 99):
      
"Good exposures of an unusual structure in the Nepean sandstone can be seen on lot 23, concession VI of North Elmsley township. A section of the sandstone shows a decisive break in bedding. Across the stratification, two conical structures occur with the apex down, about six feet high and five feet at the base of the cone (cf. photos nos. 29,  30,  31, p. 100). There is a distinct irregular banding, the bands being slightly twisted (cf. photos nos. 31, p. 100, and 32, p. 101). In horizontal section the structure is obviously concentric, forming a circle or a spiral (cf. photo. no. 33 , p. 101).  Though no other exposures of vertical sections have been found, concentric layers were observed at other places in the sandstone.”

Lots 23 and 24 of Concession VI in North Elmsley Township are a few kilometers west of Rideau Ferry and lie south of County Road 1.   Perhaps armed with the photographs I will have better luck locating the outcrops, particularly if I look in both lots.

Christopher Brett
Lanark County

A Possible Conical Fossil Near the Base of the Potsdam Group

In my blog posting for  March 2, 2017 I reported on a sandstone outcrop in Lanark County on the north side of Highway 7 approximately 5 km west of Wemyss.  This is an outcrop first reported by Dr. Easton (2015).   For that blog posting I attached three photos.   The second photo shows siltstone/mudstone layers draped over the Grenville marble and underlying a friable layer; overlain by massive  sandstone beds.

While at the outcrop I collected a loose specimen that had obviously fallen off the outcrop.  The specimen is comprised of the siltstone/mudstone layers and the friable layer.  Below are two photographs of that specimen.

In the first photograph I’ve placed a magenta box around the texture that might be a fossil.  I believe it to be a fossil (rather than dessication cracks)  because the two sides of the item are the same width and arguably represents the cross-section of a conical shape.     Further, the conical shape also arguably ends at an upper cap like shape.

In Eastern Ontario the base of the Potsdam Group is believed to be middle Cambrian in age. 
There are  numerous conical shaped fossils in the Cambrian (e.g., Volborthella, cephalopods, hyoliths), and the specimen may not be distinct enough to be identified.    

Below I’ve provided a reference to a fairly recent paper by Hagadorn  and Waggoner (2002) that is available over the internet and  which contains a discussion of the fossil Volborthella.

I’ve also provided two references to a very recent paper on hyoliths.

Anyone wanting the specimen for research purposes should send me an email.  Unfortunately it is one of those specimens where every time you pick it up another piece falls off.

Christopher Brett
Perth, Lanark County

References

Bettam, S.,  2017
U of T undergrad leads team of paleontologists, classifying mysterious ancient cone-shaped sea creatures, U of T News, Global Lens Breaking Research, January 11, 2017
https://www.utoronto.ca/news/u-t-undergrad-leads-team-paleontologists-classifying-mysterious-ancient-cone-shaped-sea
          
Easton, R. M., 2015
Project Unit 15-014. Precambrian and Paleozoic Geology of the Perth Area, Grenville Province, in Summary of Field Work and Other Activities, 2015. Ontario Geological Survey, OFR 6313
at pages 18-1 to 18- 13
http://www.mndm.gov.on.ca/en/news/mines-and-minerals/summary-field-work-and-other-activities-2015  

Hagadorn, J.W., and Waggoner, B.M., 2002
The Early Cambrian problematic fossil Volborthella: New insights from the Basin and Range, in F. A. Corsetti, ed.,  Proterozoic-Cambrian of the Great Basin and Beyond, Pacific Section  SEPM Book 93, p. 135-150.

Moysiuk, J.,  Smith, M. R.  and  Caron, J.-B., 2017
Hyoliths are Palaeozoic lophophorates,  Nature 541,   394–397  (19 January 2017)   doi:10.1038/nature20804
http://www.nature.com/nature/journal/v541/n7637/abs/nature20804.html

Ebenezer Emmons’, Sir William E. Logan’s, Professor Amadeus W. Grabau’s and Professor Greggs’ Comments on Potsdam Sandstone

I find it interesting,  when considering how the theory of the origin of  the Potsdam Group sandstones (of Ontario, Quebec and New York State)  has evolved over time, to note that numerous early writers made insightful comments, but were ignored or had their contributions overlooked.  In this posting I will mention a few of the geologists who deserve more credit.    While the title to this posting singles out Emmons, Logan, Grabau and Greggs, numerous others made insightful comments.

Ebenezer Emmons named the Potsdam sandstone.   His earliest downloadable report dates from 1842.  In this report he mentions that the Potsdam sandstone is found with conglomerate and that there a number of varieties of sandstone.  He identifies two principal varieties: 1st a sandstone variety that he subdivides into two further varieties found at quarries  (a)  at Potsdam (St. Lawrence County), and (b) at Bangor (Franklin County) and “Moore” (later spelt Mooers) ; 2nd a sandstone found at Keeseville, Whitehall and Kent, which he later says he has sometimes given “a compound name– the Potsdam and Keeseville sandstone”.  He also mentions other varieties of sandstone.    Interestingly, his sandstone from the Potsdam quarry we would now call the Hannawa  Falls Formation; his sandstone from Mooers area is likely the one we would call the Ausable Formation sandstone (for rocks in New York State; or the Covey Hill Formation, for rocks in Ontario and Quebec), and his sandstone from Keeseville we could call the Keeseville Formation (or Nepean formation, for rocks in Ontario; Cairnside Formation, in Quebec).

 In addition, Emmons comments that “Though the rock is generally even-bedded, I have noticed several places where it has been subject to violent forces, so as to greatly derange the strata”, and included drawings of folded and faulted outcrops.   He also comments on the differences in beds, singling out  materials “that appear to have been borne along by a moderate current, which has been given a diversity of stratification resembling inclined beds”, and includes a drawing of such strata, a drawing that looks like fluvial facies.

Emmons (1846) summarizes the Potsdam sandstone, summarizes  the varieties of sandstone, and notes that “In many places it is a coarse conglomerate”.

Logan makes at least the following important points:

- the Potsdam sandstone that is found in New York state extends into the Provinces of Ontario and Quebec (Logan 1844; Logan 1863)

- the Potsdam sandstones at Beauharnois which produced Protichnites trackways contain both wave ripple marks and wind ripples– they are littoral sandstones (Logan, 1860; Logan, 1861, Logan, 1863 )

- The Potsdam sandstone is better referred to as part of the Potsdam Group as the “sandstone is a member of a series of strata” and includes conglomerate  (Logan 1863)

Intriguingly, both Logan’s identification of wind ripples and his comment that the Potsdam sandstones at Beauharnois are littoral sandstones were referred to in papers published for over forty years,  but then disappeared from the literature.

Professor Amadeus W. Grabau makes the following points:

- where the Potsdam is “a transgressive overlapping series of strata deposited by a transgressing sea, the basal sand member would naturally rise in the series in the direction of transgression and overlap, and that hence a basal sand is not everywhere of the same age” (Grabau, 1909; also Grabau, 1913)

- the earlier parts of the Potsdam are of continental origin, commenting: “in many, if not in most, regions the Paleozoic series begins with a formation of continental origin, the upper portion of which was reworked by the transgressing sea”; “the Potsdam sandstone, ... in many sections, still shows characters pointing to torrential or eolian origin of a considerable portion of the rock”; and “In many cases this northern “Potsdam” sandstone shows evidence of continental origin in pre-marine time by the occurrence of well-marked torrential cross-bedding in parts which apparently have not been reworked.”

- the Potsdam sandstone includes both quartz sandstone and arkosic sandstone (Grabau, 1920).

Professor Greggs, in combination with co-authors from the Geology Department at Queen’s University at Kingston, differentiated between typical Nepean and typical Potsdam (Hannawa Falls) sandstones, finding that both occurred in Ontario and both occurred in New York State, noting that “These sandstone units  appear to bear consistent stratigraphic relationships to one another” [Greggs and Bond, 1972].  Further, “Periods of erosion punctuated the development of the Potsdam sandstones (Cushing, 1910; Chadwick, 1919; Clarke, 1966), and at some stratigraphic horizon not yet determined by detailed field studies, the environment of deposition of the Potsdam appears to have changed from continental, wind-blown sandstones, possibly reworked by coastal waters, to a shallow marine depositional environment.” [Greggs and Gorman, 1976]

Interestingly, Professor Greggs’ distinction between the shallow marine Nepean sandstone and typical continental, wind- blown Potsdam (Hannawa Falls) sandstone in part reflects the distinction drawn by Ebenezer Emmons (1842) who distinguished between the variety at Keeseville and the other at Potsdam, St. Lawrence County.  

(Numerous others who studied and reported on the rocks of New York State, including Professor Cushing, distinguished between the varieties of Potsdam sandstone.   There are just too many to summarize.)

Christopher Brett
Perth, Ontario

References

Emmons, Ebenezer, 1842
Survey of the Second Geological District, In Geology of New York, Part II; W. & A. White & J. Visscher, Albany, New York

Emmons, Ebenezer, 1846
Agriculture of New York;   C. Van Benthuysen & Co., Albany, New York

Grabau,  Amadeus W., 1909
Physical and Faunal Evolution of North America during Ordovicic, Siluric, and Early Devonic Time, The Journal of Geology, Volume 17, 209-252

Grabau, Amadeus W., 1913
Principles of Stratigraphy; A.G. Seiler and Company, New York

Grabau, Amadeus W., 1920
A Comprehensive Geology; Part 1, D. C. Heath & Co., New York           

Greggs, R. G.  and Bond, 1972
A principal reference section proposed for the Nepean  Formation of probable  Tremadocian age near Ottawa, Ontario. Canadian Journal of Earth Sciences, 9, pp. 933-941.

Greggs, R.G.  and Gorman, W.A.  1976
Geology of the Thousand Islands,  by Parks Canada
http://www.oliverkilian.com/ecology/thousand-islands/island-insights/geology/rocks.html

 Logan, W. E.,  1844
Geological Survey of Canada, Report of Progress For the Year 1843

Logan, W. E., 1860
On the Tracks of an Animal lately found in the Potsdam Formation ,  read before the Natural History Society of Montreal in June, 1860, volume V of The Canadian Naturalist and Geologist, article XXXIX, pages 279-285

Logan, W. E., 1861
Considerations relating to the Quebec Group, and the Upper Copper-bearing Rocks of Lake Superior;  read before the Natural History Society of Montreal in May, 1861, volume VI of The Canadian Naturalist and Geologist, page 199-207

Logan, W. E., 1863
Geology of Canada, Geological Survey of Canada, Report of Progress from its commencement to 1863,