Tuesday, 4 November 2014

Layering in the Mealy Mountains Anorthosite Complex, Labrador

In my last posting I mentioned that I had seen spectacular layering in anorthosite intrusions in Labrador.  Below are photographs that I took of layering in the anorthosite plutons that form the Mealy Mountains in Labrador.  The person that is the scale in the photographs is Dr. Ron Emslie of the Geological Survey of Canada, who was about average height for a world renowned expert on anorthosites.
















Ron described the layering as follows:
“Within leucotroctolite, leucogabbro and anorthosite, igneous mineral layering on a scale of 1 cm to 10 m, or more, is common (Fig. 33. 2). Where rock exposure is good, layers or layer contacts can be found on most clean subvertical rock surfaces more than a few metres high. In leucotroctolite the mineral layering involves differences in proportions of olivine and plagioclase,
whereas in leucogabbro and anorthosite, variations in pyroxene and plagioclase proportions are the chief cause. In addition to mineral layering, manifestation of layers is due to differing plagioclase grain sizes and shapes and in some cases, plagioclase colour particularly in leucogabbro and anorthosite. Dark layers in some anorthositic rocks were found to consist of darker coloured plagioclase than that in the enclosing host rock. Such "dark plagioclase" layers were evident in some places even where the enclosing rock contained a noticeably higher proportion of ferromagnesian minerals. Large areas of the complex have relatively consistent layering attitudes. For example, the northwestern part of the complex has dips to the northwest
and west at angles less than 30 degrees. Other areas have remarkably discordant layer attitudes over short distances and sometimes even within the same outcrop. Such discordance seems to be a primary igneous feature of the crystal accumulation process and is not due to superimposed deformation.”

(Emslie, R. .F (1976), Mealy Mountains Complex, Grenville Province, Southern Labrador,
Report of Activities Part A; Geological Survey of Canada, Paper no. 76-1A; p. 165-170
http://geoscan.nrcan.gc.ca/starweb/geoscan/servlet.starweb?path=geoscan/fulle.web&search1=R=123988
http://ftp2.cits.rncan.gc.ca/pub/geott/ess_pubs/119/119844/pa_76_1a.pdf )


Christopher Brett
Perth, Ontario

Suggested Readings

Emslie, Ronald F.  (1975),  Nature and Origin of Anorthosite Suites, Geoscience Canada, Volume 2, Number 2, pages 99-104
http://journals.hil.unb.ca/index.php/GC/article/view/2912
   
Emslie, Ronald F. (1980) , Geology and Petrology of the Harp Lake Complex, Central Labrador- an example of Elsonian Magmatism.  Geological Survey of Canada, Bulletin 293, 136 pages
http://data.gc.ca/data/en/dataset/96d2a3bc-c79d-57f1-8169-24e01d431893

Hamilton, Michael A. , Scoates, James S. and Rämö, O. Tapani  (2010)
The Petrology of Anorthosites, Related Granitic Rocks, and UHT Assemblages: a Tribute to Ronald F. Emslie, Can Mineralogist, volume 48, pages 705-710
http://canmin.geoscienceworld.org/content/48/4/705.full


Monday, 27 October 2014

Layering in the Lavant Gabbro Complex, Lanark County, Ontario

The Lavant Gabbro Complex, which lies northwest of Perth,  is purported to be the largest mafic body in the Grenville Province of Ontario.  It covers approximately 250 square kilometers.

 The following simplified geologic map shows the extent of the Lavant Gabbro Complex.




The towns of Lanark, Almonte, Carleton Place and Clyde Forks are shown on the map.  The town of Perth is under  the Legend.

The Lavant Gabbro Complex falls within the Sharbot Lake Terrane (sometimes called the Sharbot Lake domain)  of the Central Metasedimentary Belt of the Grenville Province, Canadian Shield.   The Sharbot Lake Terrane is comprised of marbles and metavolcanic rocks that have been intruded by gabbroic and granitic plutons.   It is bounded on the east by the Maberly shear zone and on the west by the Robertson Lake shear zone (sometimes called the Roberton Lake mylonite zone).   The metavolcanic rocks falling within the Sharbot Lake Terrane are not shown on the above  map. 

Much of the Lavant Gabbro Complex  was mapped in detail in the 1980's by Liba Pauk, J. M. Wolff  and Michael Easton of the Ontario Geological Survey, and outcrops of the complex can be easily found along a number of roads that cross the complex. 

Fernando Carfu and Michael Easton in a paper published in 1989 described the complex as follows:

“The Lavant gabbroic complex is a composite intrusion, roughly 50 km long and up to 15 km wide.   It consists of (i) a voluminous mafic suite, dominated by medium-grained gabbro to diorite, locally showing igneous layering and crosscutting relationships between several compositionally distinct phases; and (ii) a slightly younger granodiorite–monzogranite suite, which forms several small intrusive bodies and dikes cutting the gabbro.  The intermediate to felsic phases occur mainly in the structurally higher part of the complex, and also intrude adjacent supracrustal rocks, including the marbles.  Metamorphic grade of the complex varies from upper greenschist facies in the north to lower amphibolite facies in the south.   Contact relationships are complex, and inclusions, roof pendants and slivers of all the country rocks are present.  The gabbro body does not have an extensive contact aureole...”

They determined an age of 1224 ± 2 Ma for the gabbroic and associated monzogranitic rocks of the Lavant complex.

I’ve always been interested in layering in igneous rocks, and saw numerous examples of layering in anorthosite bodies in Labrador when I was employed as a summer student by the Geological Survey of Canada.  I wondered whether any examples of layering in the Lavant Gabbro complex could be easily found.

In her Report 253 published in 1989 Liba Pauk of the Ontario Geological Survey mentioned:

“Primary rhythmic and graded layering of pyroxene cumulus occurs in a roadcut 1.2 km northwest of Black Creek Meadow (Photo 5).  The layers strike 90 degrees and dip 30 degrees to the south.  The primary rhythmic layering was also recorded ... some 1.5 km east of the map area at roadcuts of Lavant County Road 16.”

Her Photo 5 shows spectacular layering.  The caption to her photo reads: Primary graded rhythmic layering in the Lavant Gabbro Complex.   The only exposure found in the map area is located along Joes Lake Road, 1.2 km northwest of Black Creek Meadow.”

I did find her outcrop, but as it is now overgrown and covered with moss or lichen,  the layering is no longer visible.   For those looking for the outcrop, please note that the “Joes Lake Road” mentioned by Liba Pauk has been renamed Black Creek Road, and that the outcrop is on the east side of the road 1.3 km north of where Black Creek crosses the road.  (More importantly, the current Joes Lake Road that is just south of Joes Lake is not the Joes Lake Road mentioned by Liba Pauk.)

In a paper published in 1994 Graham C. Wilson of the Ontario Geological Survey  mentioned:
   
“The best layering observed in this area, and indeed in the course of the whole project, was observed in a satellite body on the east side of the main intrusive mass, west of Hopetown. The layers (Fig. 5c) are graded, and reflect modal variation between light feldspar and dark minerals (pyroxene or secondary amphiboles).”

Figure 5c appears at page 147 of Wilson’s report 5580.   It shows spectacular layering.  I did not find that outcrop, but did find two outcrops west of Hopetown on the north side of County Road 16 (a kilometer or so west of Highway 511)  that show layering in the gabbroic rocks.  Below are photographs of the two outcrops:








While the layering in the second outcrop is much better than the photograph shows, neither outcrop compares with the spectacular layering that  I saw in Labrador.

In his Report 5693 published in 1988 Michael  Easton of the Ontario Geological Survey also reported on  primary igneous layering within the Lavant Gabbro Complex, which he mentioned  consisted “of a variety of gabbro phases, ranging from gabbro to diorite to pyroxene gabbro to gabbroic anorthosite.”   I have not yet found the time to look for his occurrences.   
   
Christopher Brett
Perth, Ontario



References and Suggestions for Further Reading

Carfu, Fernando and Easton, R. Michael (1989), Sharbot Lake terrane and its relationship to Frontenac terrane, Central Metasedimentary Belt, Grenville Province: new insights from U-Pb geochronology, Can. J. Earth Sci. 34: 1239-1257
http://www.nrcresearchpress.com/doi/pdf/10.1139/e17-099

Easton,  R. Michael (1988), Geology of the Darling Area  Lanark and Renfrew Counties; Ontario Geological Survey, Open File Report 5693, 206 pages, at pages 60-66, Accompanied by Map 3113
http://www.geologyontario.mndmf.gov.on.ca/mndmfiles/pub/data/imaging/OFR5693/OFR5693.pdf

Easton,  R. Michael and DeKamp, E.A. (1987),  Darling Area,  Lanark and Renfrew Counties; Report 34 at  pages 220-228, in Ontario Geological Survey Miscellaneous Paper 137, Summary of Field Work and Other Activities 1987

Pauk, Liba (1989a), Geology of the Dalhousie Lake Area, Frontenac and Lanark Counties; Ontario Geological Survey Report 245, 57 pages, at pages 17-23, Accompanied by Map 2512
http://www.geologyontario.mndmf.gov.on.ca/mndmfiles/pub/data/imaging/R245/r245.pdf
                   
Pauk, Liba (1989b), Geology of the Lavant Area, Lanark and Frontenac Counties; Ontario Geological Survey Report 253, 61 pages, at pages 26-29, Accompanied by Map 2515
http://www.geologyontario.mndmf.gov.on.ca/mndmfiles/pub/data/imaging/R253/R253.pdf
   
Wilson, G.C. (1994), Mafic-ultramafic intrusions, base-metal sulphides, and platinum group element potential of the Grenville province of southeastern Ontario: Ontario Geological Survey, Open File Report 5880, 196 pages at pages 125-128
http://www.geologyontario.mndmf.gov.on.ca/mndmfiles/pub/data/imaging/OFR5880/OFR5880.pdf

Wolff, J. M., 1985, Geology of the Sharbot Lake Area, Frontenac and Lanark Counties, Southeastern Ontario; Ontario Geological Survey Report 228, 70 pages at pages 29-37, accompanied by Map 2471
http://www.geologyontario.mndmf.gov.on.ca/mndmfiles/pub/data/imaging/R228/R228.pdf   




Wednesday, 17 September 2014

Lake Iroquois and the Glaciofluvial Deltaic Deposit at Joes Lake, Lanark Highlands, Ontario

About 18,000 years ago the Laurentide Ice Sheet reached its maximum thickness and  southward extent, covering Eastern Ontario with a thickness of over two kilometers of ice, and extending southward to New York City.   The southern edge of the glacier then started to retreat northward.  In the 1,500 year period starting about 12,500 years ago eastern Ontario changed from ice covered to ice free.   As the edge of the glacier retreated northward melt water from the retreating glacier formed a proglacial lake,  Lake Iroquois, a precursor of Lake Ontario.  Lake Iroquois covered all of present day Lake Ontario and extended northward abutting on the retreating glacier.   In its early stages Lake Iroquois covered Kingston and all of Prince Edward County, and then grew larger and extended northward as the glacier retreated.   There were two factors that allowed Lake Iroquois to extend northward and cover what is now dry land.   First, the weight of the Laurentide Ice Sheet had depressed much of Eastern Ontario from 175 to 230 meters.  Second, the retreating glacier formed an ice dam that prevented Lake Iroquois from draining down what is now the St. Lawrence River.  (The lake drained from an outlet at Rome, New York and then to the Hudson River.)

Twenty-two years ago Inez M. Kettles of the Geological Survey of Canada issued a report on the glacial deposits in Lanark, Frontenac and Leeds Counties.   (See:  Kettles, I.M., 1992, Glacial Geology and glacial sediment geochemistry of the Clyde Forks - Westport area of Ontario, Geological Survey of Canada, Paper 91-17.  The report can be downloaded from:
http://geoscan.nrcan.gc.ca/starweb/geoscan/servlet.starweb?path=geoscan/fulle.web&search1=R=133492).  

Inez Kettles  reports that glacial Lake Iroquois covered much of Lanark County, extending at least as far northward as Joes Lake in the Township of Lanark Highlands.   (Joes Lake is the name of both a lake and small village.  It is about 45 kilometers north west of Perth and is known for its fishing and magnificent views.  It is named for an Algonquin who had a camping spot over the lake and was known to walk to and from Perth. I drove.)       

Inez Kettles reported a large delta at Joes Lake that she identified as a proglacial subaerial outwash that she believes was built within 3 km of the retreating ice margin.  She mentions that “The exact position of the ice margin as the delta  was forming, is however, uncertain and it is possible that the delta is an ice contact deposit.  The cobbly, bouldery texture of some foreset beds exposed at Joes Lake and the presence of a well developed kettle hole on the delta surface indicate that these sediments were deposited close to the ice.  It is also possible that some sediments mapped as ice contact glacial deposits in the channel north of and leading to the delta, were deposited as proglacial outwash.”

Last year Victoria Lee of the Ontario Geological Survey issued a report on the aggregate resources of Lanark County that covered the glacialfluvial deposits, including the gravel pit at Joes Lake.   (See, Lee, V.L. 2013, Aggregate resources inventory of the County of Lanark, southern Ontario: Ontario Geological Survey, Aggregate Resources Inventory Paper 189, 85 p.    Her report can be downloaded from:
http://www.geologyontario.mndmf.gov.on.ca/mndmfiles/pub/data/imaging/ARIP189/ARIP189.pdf   )  

When discussing the deposit at Joes Lake Victoria Lee  mentions:   “The deposit is a large glaciolacustrine deltaic deposit.  The delta is inferred to have been deposited close to the ice margin ... The deposit material, ranging from cobble-sized to silt, is well sorted with distinct layers of cobbles, gravel, sand and silt-rich layers.  ... Well-defined terraces mark the boundaries of the deposit.  One licensed pit (Pit No. 3) and one unlicensed pit (Pit No. 55) have been developed in the resource area.  Face heights in the pits range from 4 to 10 m; however, available borehole records indicate the potential for more than 15 m of sand and gravel locally.  Calcite cementation within the deposit holds material 30 degrees off the vertical and cause potential problems during extraction...”

Below are photographs  taken at the sand and gravel pit in the proglacial subaerial outwash deposit just to the north of Joes Lake along the Lavant Darling Road.


The last two photos show underlying beds of cobbles and sand that are truncated by later deposited layered  beds of cobbles and sand.

Inez Kettles’ report covers large parts of Lanark, Frontenac and Leeds counties.  Figure 10 to the report is a map that covers Clyde Forks, Sharbot Lake, Tichborne, Westport, Morton, Smiths Falls and Carleton Place.   It shows selected glaciofluvial deposits and glacial striae, and gives a good indication of the direction the glacier was moving.   Figure 11 shows the distribution of drumlins in the Clyde Forks, Westport, Smiths Falls and Ottawa area.  Both figures are worth a look.

In 1936 A.P. Coleman of the Ontario Department of Mines published a report on Lake Iroquois with an accompanying Map No. 45f entitled Lake Iroquois and Related Ice Front at the Time of the Rome Outlet  (Scale, 5 miles to the inch).    It is worth a look.  Below I’ve provided a copy of the map.  The part shaded green is the retreating glacier.  The part in blue, which covers Prince Edward County and Kingston, is Lake Iroquois.






The copy doesn’t do justice to the map, which can be downloaded from http://www.geologyontario.mndmf.gov.on.ca/mndmfiles/pub/data/imaging/ARM45F/ARM45F.pdf

Christopher Brett
Perth, Ontario




Wednesday, 20 August 2014

A Selection of Fossils from the March Formation in Lanark County, Ontario - Part 2

My posting entitled A Selection of Fossils from the March Formation in Lanark County, Ontario  from  September 13, 2013 contained photographs of fossils from a quarry in Lanark County about a five minute drive north of Perth.   On Tuesday I was at the quarry to order a load of gravel for my driveway, and took the opportunity to look for fossils.  Below are photographs of three surfaces that show burrowing parallel to the bedding plane.  Two photographs are provided for each surface.


Interestingly, the quarry manager told me that they have crushed 65,000 tons of rock since I was there last.

Christopher Brett
Perth, Ontario

Thursday, 14 August 2014

Blasting of Outcrops Along Highway 15, including at Elgin

Since the spring the Province of Ontario has been widening Highway 15 between Crosby and the turn off at Hwy 32 to Gananoque, and has been blasting most of the outcrops along Highway 15.   A lot of fresh rock has been exposed.  Unfortunately, most of the blasted rock has been used to construct the roadbed for the new highway (rather than being saved for geologists and rock hounds).
               
The geology is complicated.  There are good outcrops of Potsdam Group sandstone of late Cambrian age, and outcrops of Precambrian plutonic igneous rock and Precambrian high grade metamorphic rock.   The Precambrian basement rocks are part of the Central Metasedimentary Belt of the Grenville Province.   I mentioned in my last posting that the Central Metasedimentary Belt is subdivided into a number of terranes.   Each of these terranes is characterized by distinct rock assemblages and mineral deposits.   This stretch along Highway 15 falls within the Frontenac terrane of the Central Metasedimentary Belt.   The Frontenac terrane comprises metamorphosed sedimentary rocks (metaquartzite, quartzofeldspathic gniesses, marble), lacks volcanic rocks, and was affected by the intrusion of plutonic rocks and intense metamorphism in the period of about  1190-1160 Ma.   The Frontenac Terrane is preserved at upper amphibolite to granulite facies.

Wynne-Edwards (1967), who conducted the most comprehensive study of these rocks, concluded that the “metamorphic rocks most reasonably represent a sequence of marine sediments deposited in a stable area of relatively shallow water, and brought by deep burial into a metamorphic environment with high temperature and confining pressure [where they were intensely deformed, folded and refolded.]  ...The metasedimentary rocks of the Westport map-area are dominantly stratiform quartz-biotite-feldspar gneisses, coarsely crystalline calcite marble ... and smaller amounts of quartzite...   Granitic material in the form of pods, layers or lenses is present in all these rocks. ...  In addition to this granitic material, large concordant plutons of quartz monzonite and monzonite occur at certain places, particularly in belts of crystalline limestone.  These monzonites post-date the main period of metamorphism and have altered gabbroic rocks previously emplaced at the same sites.  Diabase dykes and younger porphyritic andesite dykes cut all these rocks. ...
    An extended period of erosion before the deposition of the Paleozoic rocks exposed the highly metamorphic rocks at the surface and established much of the existing topography.   In some places the ancient land surface is preserved as a deep zone of oxidation and weathering below the Nepean sandstone.”

(Wynne-Edwards, H. R., 1967,  Westport map Area, Ontario, With Special Emphasis On the Precambrian Rocks, Geological Survey of Canada, Memoir 346, 142 pages at pages 108, 4 and 5
http://geoscan.nrcan.gc.ca/starweb/geoscan/servlet.starweb?path=geoscan/fulle.web&search1=R=100533  )

Below I’ve provided an extract from the Geological Survey of Canada’s Map 1182A, Westport, Ontario,  compiled by H.R. Wynne-Edwards.  This shows the geology along Highway 15 from Crosby (at the top left  corner of the map) to south of Morton.  The large pink oval shape at the bottom right corner of this map extract is the Lydnhurst quartz monzonite pluton.






Below is part of the legend for Wynne-Edwards’ geologic map.






The complete map can be downloaded from http://geoscan.nrcan.gc.ca/starweb/geoscan/servlet.starweb?path=geoscan/fulle.web&search1=R=108032
   
Those that have driven along Highway 15 this past summer will have noted that the outcrops of Potsdam Group sandstone at Elgin have changed.   In some ways you can see more as the rock is fresh, but some of the  weathered surfaces are gone.  Below are photographs of three sandstone outcrops near Elgin (the first two showing the unconformity) .
Sam_0544  - Northeast corner of Hwy15 and the main road into Elgin
Sam_0547 - other side of Hwy 15
Sam_0552  - just south of Elgin, west side of road


 (If you visit, you might consider taking a stiff  broom to clear off the outcrops..)

Below is a photograph of an outcrop of Nepean Formation, Potsdam Group, sandstone.  This outcrop is north of Morton on the east  side of Highway 15.  The ruler is  along an inch thick bed of rounded quartz pebble conglomerate that extends the length of the outcrop.

Below I’ve provided photographs of outcrops of gneiss at and just south of Morton, together with close up photographs of pods of granitic material in the gneiss.









 South of Morton there are also fresh outcrops of Wynne-Edwards’ Lydnhurst quartz monzonite pluton


I’ve found that looking at the outcrops on the weekends works best, as you do not have to dodge the construction vehicles. 

Christopher Brett
Perth, Ontario

 +++++++++++++++++++++
Addendum: 

Wynne-Edwards (1967)  did not place the Precambrian rocks that he mapped within a plate tectonics setting, as the theory had not been extended to the Precambrian at the time he conducted his field work and published his memoir.   Since that time  the general adoption of the theory has led to these rocks being placed in a plate tectonics setting.   See, for example:

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,

James M. McLelland, Bruce W. Selleck and M.E. Bickford (2010), Review of the Proterozoic evolution of the Grenville Province, its Adirondack outlier, and the Mesoproterozoic inliers of the Appalachians, The Geological Society of America, Memoir 206, p. 1-29.

Jeff Chiarenzelli, Sean Regan, William H. Peck, Bruce W. Selleck, Brian Cousens, Graham B. Baird and Catherine H. Shrady (2010), Shawinigan arc magmatism in the Adirondack Lowlands as a consequence of closure of the Trans-Adirondack backarc basin,  Geosphere 2010;6;900-916

All are available online. 




Thursday, 17 July 2014

An Outcrop that Records the Eruption of Pillowed Basaltic Lava

In an earlier posting I listed various field trip guides, including A. Davidson’s 1995 field trip guidebook on the Grenville Province of the Canadian Shield, and singled out Stop 5-10,  which is a photogenic outcrop of pillowed basalts at the junction of County Roads  41 and 506  south of Bon Echo Provincial Park,  and north of Kaladar.   This past  weekend, while driving to Peterborough down Highway 7, I took a short jog up Highway 41 to visit the outcrop, which is  just south of Cloyne.  Below are four photographs of this glacially polished, pillowed basalt outcrop.







The rounded form of the pillows results from the rapid cooling of basaltic magma that erupts under water.   Volcanoes that produce such basalts occur along mid-ocean ridges.  The pillows at this location have been stretched during regional metamorphism.
   
Davidson describes the outcrop as follows:

“Stop 5-10.  Pillowed basalts, Tudor formation, Grenville Supergroup
Mafic volcanic rocks along this stretch of highway lie on the east side of the ~1.27-Ga Elzevir tonalite batholith, which intrudes them.  Pillows at this stop indicate the flows face away from the batholith.  The metabasalts have tholeiitic chemistry; higher in the stratigraphic succession to the east lie andesitic and coarse volcaniclastic rocks that are clearly calc-alkaline....”

[A. Davidson, 1995,  Tectonic History of the Grenville Province, Ontario
Field Trip Guidebook A5, Precambrian ‘95, Geological Survey of Canada, Open File 3142
http://ftp2.cits.rncan.gc.ca/pub/geott/ess_pubs/205/205286/of_3142.pdf ]

I recently found on the web a field trip guide prepared last year by graduate geology students at Ottawa University and Carleton University which includes four stops at volcanic rocks in the area south of Bon Echo Provincial Park and north of Kaladar.   They describe the pillowed basalt outcrop as follows:

“Stop 2– Tudor Pillow  Basalts - Highway 41 and Highway 506 intersection
This outcrop includes pillowed basalts belonging to the Tudor suite (erupted >1265 Ma),
which display various primary igneous textures such as pillow selvages, hyaloclastite and vesicles. The preservation of these textures allows us to determine which way the pillows were oriented upon eruption ... which way is it? This preservation of primary textures is rare within rocks of the Central Metasedimentary Belt, which has experienced multiple metamorphic events and several intense deformation events (i.e. the Elzevir, Shawinigan and Ottawan orogenic  events)”

[ Seamus Magnus, Dave Lowe, Jamie Cutts, and Travis McCarron, 2013,
OCGC Field Trip – September 27th to 29th 2013
earthsci.carleton.ca/sites/default/files/Field%20Guide%202013.pdf ]

Magnus, Lowe, Cutts and McCarron give directions to three other nearby outcrops of volcanic rocks.  Here is an abridged version of their description:

Stop 1 – Mazinaw Lake Metavolcanics
North of Highway 41 and Mazinaw Road intersection
This outcrop contains intermediate to felsic volcaniclastic rocks of the Mazinaw Lake formation (1240-1250 Ma). ... , volcanic breccias and volcaniclastic rocks such as the tuffs observed in this outcrop. ...
Stop 3    – Metavolcanic and Metasedimentary Contact North of O’Donnell Road
Mafic metavolcanic rocks (west) and metapelitic rocks (east) are present on either side of
a small trodden path. This path represents an unconformable contact between the two
units. ...
Stop 4– Kashwakamak Hornblende Dacite
333199E, 4964264N – Ladyslipper Road, off of Myers Cave Road, south of lake
A calc-alkaline dacitic rock erupted at 1276 ±2 Ma (U -Pb zircon).... Interpreted as either a flow or dome, this represents the less dramatic form of intermediate volcanism.”

Given extra time, I would have visited those outcrops.    The pillowed basalt, as noted above, records an eruption along  a  mid-ocean ridge.   Dacite is believed to form when basaltic rocks are dragged down and melt along a subduction zone.  

These rocks occur within the Mazinaw Terrane of the Central Metasedimentary Belt (“CMB”) of the Grenville Province of the Canadian Shield.  Professor Nick Eyles of the University of Toronto commented in 2002 on the Central Metasedimentary Belt as follows:

“A number of different blocks (terranes) occur within the CMB (e.g., Bancroft, Elzevir, Mazinaw) and are separated by shear zones (large faults) that record the slippage between each terrane as they were pushed together.  These terranes were separate land masses (basically micro-continents) with intervening seas which were swept together during the Grenville Orogeny.

Some geologists have suggested that modern-day Indonesia , with its subduction zones and limestone reef-fringed volcanic islands, provides a good model for the CMB.  Rocks include pillow basalts, typical of oceanic crust, and pyroclastic debris deposited around explosive andesitic volcanoes at modern subduction zones.   Mud and gravel that accumulated in the surrounding deep waters were deformed to schist and conglomerate.    Other common metamorphic rocks are marbles formed from the alteration of limestone and quartzites derived from quartz rich sandstones. ...”

[Nick Eyles, 2002, Ontario Rocks - three billion years of environmental change, Fitzhenry & Whiteside, 339 pages, at page 105 ]

Professor Dugald Carmichael of Queen’s University at Kingston has commented on the rocks of the Central Metasedimentary Belt as follows:

“Starting about 1280 million years ago, ... volcanic eruptions created a chain of islands in the ocean. Like the present-day Antilles or the Philippines, these volcanic islands would have formed along the boundary between two converging tectonic plates. The islands grew larger as basaltic lava erupted from vents and fissures above and below sea level. Later the eruptions became violently explosive, spewing vast amounts of volcanic ash and cinders. In shallow intertidal lagoons around the islands, blue-green photosynthetic bacteria built small laminated mounds on a seafloor of precipitated calcium carbonate. Volcanic ash was eroded from the islands and washed into the lagoons, where later it consolidated into sandy limestone and limy shale. Deep underground beneath the volcanoes, between 1270 and 1240 million years ago, huge volumes of molten magma cooled and crystallized into granite and other types of igneous rock.

Meanwhile a continent, riding on a converging tectonic plate, was approaching the chain of islands. As the intervening ocean narrowed, submarine landslides broke loose from the leading edge of its continental shelf and slumped down the continental slope, mixing with mud to make a spectacular sedimentary breccia. When the continental shelf collided with the chain of volcanic islands, a great range of mountains was uplifted. Cobbles, pebbles, sand and clay were eroded from the mountains and deposited in sedimentary formations atop the eroded surface of what had been the chain of islands. Continuing tectonic convergence squeezed the sedimentary formations into tight folds, and all the older rocks were also squeezed. Deep underground, between 1170 and 1080 million years ago, high temperature and pressure changed the sedimentary and igneous rocks into metamorphic rocks, and once again granitic magma intruded, cooled and crystallized.’

[Bedrock in the Frontenacs, by  Dugald Carmichael,
http://naturallyrichfrontenacs.com/bedrock.html ]

 Food for thought when you are driving down Highway 7.

Christopher Brett
Perth, Ontario   


Thursday, 22 May 2014

Andrew Dickson, a Founder of Pakenham, Sheriff of Bathurst District, and Geologist

“With the early progress and development of Geology of Canada, the name of Andrew Dickson will always be honorably associated.”
(The Canadian Journal of Industry, Science and Art.  July, 1855)

Andrew Dickson (1797 - 1868), the person most associated with the founding of the Village of  Pakenham in Lanark County, is principally remembered today as Sheriff Dickson, as he held the position of Sheriff of Bathurst District for a ten year period from 1842 to 1852.   At that time Bathurst District encompassed what today is Lanark County, Renfrew County and Ottawa west of the Rideau River.   Perth was the most important town in Bathurst District, while Ottawa (then known as Bytown) was a small lumber town.   An article on Sheriff Dickson published in 1915 in the Almonte Gazette points out  that “when Perth was the judicial, educational and social centre of this part of Ontario, it was a striking sight to see Sheriff Dickson in his shrieval garb, armed, astride his fine horse, taking prisoners from Bytown, to the district gaol in Perth, the prisoners being also mounted on horses and chained to the sheriff.”

Andrew Dickson had a varied career.   He was born in Scotland in 1797 and came to Canada in 1819 to take charge of a lighthouse in Nova Scotia.  He came to Perth in 1821 and then settled in Fitzroy township in 1823 as a farmer.  In 1831 he purchased the mill, river rights and the land in Pakenham township where the Village of Pakenham now stands.  ‘Dickson’s Mills’ began to grow.  For a number of years Andrew Dickson carried on a lumbering and mercantile business, and later added a carding mill.  He held a shop license for the sale of spirituous liquors.  He built a lumber slide and charged a toll on all logs passing downstream.  He operated a limestone quarry on his land.  He set up grinding wheels powered by his mills to polish limestone slabs that were used locally as ornamental stone.  He was Dickson’s Mills first postmaster.  He built Dickson’s Mills first church.   He laid out the village plot for Pakenham, and registered it under the name of Pakenham.   In 1835 he was appointed Commissioner of the Courts of Bequests for the District of Bathurst.  In 1842 he was appointed Sheriff of Bathurst District.  In 1852 he resigned as sheriff to accept the position as Inspector of the Provincial Penitentiary, when he moved to Kingston, Ontario.  In 1858 he was appointed Warden of the Reformatory Prison of Lower Canada and moved from Kingston to Isle Aux Noix.  In 1860 he returned to Pakenham where he resided until his death in 1868.

In addition to his business interests, Andrew Dickson was a hunter, curler, and Lieutenant-Colonel in the militia.  He was also a noted amateur geologist, was elected a member of The Canadian Institute in 1854 and was a member of the Historical and Literary Society of Quebec.   Invariably, articles  referring to Andrew Dickson refer to him as Sheriff Dickson, and stress this part of his career.   It is as a geologist that he should also be remembered.

In a book published in 1925, entitled Pioneer Sketches in the District of Bathurst, Andrew Haydon devotes Chapter VII to Andrew Dickson, Sheriff– A Pioneer of Pakenham.  Haydon mentions that “The distinguished geologist, Sir William Logan, was among Mr. Dickson’s personal friends.”    Haydon also mentions  that “On the Dickson farm at Pakenham here had been opened during the building of the railway a fine quarry of limestone.... in this quarry he had discovered fossil remains in plenty and of a variety for which the much-coveted Bigsby medal had been founded and granted by the Royal Geological Society of England, while yet, outside of Mr. Dickson’s discovery, the fossil was yet almost unknown to the scientific world.”   Haydon also mentions that Andrew Dickson exhibited at the Universal Exhibition in 1855 specimens of wood, specular iron, marble, shell marl and sandstone.

The article  published in 1915 in the Almonte Gazette mentions both that “ He was one of the most enthusiastic and intelligent geologists in Canada, and succeeded in making a fine collection of specimens. In this connection he rendered material aid to his personal friend, Sir William Logan, in tracing and developing the mineral resources of Central Canada.” and that “A few years ago, when Dr. Ami, the Ottawa geologist, returned from a business trip to the British Museum, he reported that some of the specimens there were known as the "Dicksonia" specimens, in honor of the subject of this sketch.”
   
An online article entitled Mining in Lanark County mentions that “Sheriff Dickson lectured on geology for the benefit of the Mechanic’s Institute.”   I assume these lectures were at Perth’s Mechanics Institute (established in 1844) which in 1903  became the Perth Library, though they may have been given at the Carleton Place Library Association and Mechanics’ Institute (founded 1846).    (Mechanics' Institutes were used as libraries for the adult working class, also provided lecture courses, and in some cases contained a museum.)

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The original sources provide more information on Sheriff Dickson’s contributions to the understanding of geology in what is now Ontario.   His help was acknowledged by the leading Canadian geologists of his era, including Sir William Logan, Elkanah Billings and Sir John William Dawson.

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On at least three occasions Sir William Logan thanked Andrew Dickson.

First, in his Report of Progress for the year 1845-46, when he discusses the geology of the Ottawa River and some of its tributaries, he mentions that  “Ascending the Chats Lake, we made an excursion up the Mississippi River to Pakenham, where Mr. Dickson, the founder of this thriving village, who takes an interest in geological phenomena, was so obliging as to accompany me to several spots in the vicinity, and to supply me with a small collection of specimens illustrative of the rocks of the Township;”

Logan, W.A., 1847, Geological Survey of Canada, Report of Progress for the year 1845-46, at page 9.
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Second, in answer to the question “Do you think any material advantage might be derived from voluntary assistants?” asked by the Select Committee on the Geological Survey of Canada, William Logan answered in 1855 that “There can be no doubt of it.   In localities in their own neighbourhood, I have received valuable information from various persons, to whom I have been careful on all occasions to render public thanks.  Among those that have favoured me are Mr. Abraham, Dr. Wilson, the Rev. Mr. Bell, Mr. Billings and Mr. Sheriff Dickson .  An excellent vein of geological knowledge seems to run up the Ottawa.” 

Harrington, Bernard  J., 1883, Life of Sir William E. Logan , John Wiley & Sons, New York, at page 288.
Report of the Select Committee on the Geological Survey of Canada– Minutes of Evidence,
The Canadian Journal of Industry, Science and Art,  1854'5 , Vol. III,  pages 250 - 256 at 254.

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Third, Sir William Logan acknowledges Sheriff  Dickson’s help in the acknowledgments to his book the  Geology of Canada, where he mentions that “ we are indebted to Mr. A. Dickson of Pakenham for various facts relating to the Post-tertiary formation, and for specimens from this, and from the Lower Silurian rocks.”
   
Later in the book Sir William Logan relies on Andrew Dickson when he states: “The latter appears to form an isolated patch on the Chazy, in the neighborhood of Dickson's mills in Pakenham ; where, as has already been stated, it is brought, by a dislocation, against the Calciferous, on the  south side. Near the mills, the Birdseye and Black River formation  yields very large masses of Columnaria alveolata, and some of its beds abound with great orthoceratites, the chambers of which have occasionally been found by Mr. Dickson to hold large quantities of petroleum.”
       
Logan, W.A., 1863, Geology of Canada, Geological Survey of Canada, Report of Progress from Its Commencement to 1863; at Pages x and 175

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Elkanah Billings, Canada’s foremost paleontologist, singled out Andrew Dickson by naming the  fossil Agelacrinites Dicksoni after him.

Agelacrinites Dicksoni, Billings 
Plate VIII.  Figs. 3, 3a, 4, 4a

“I have dedicated this species to Andrew Dickson, Esq., of Kingston, C. W., one of the best workers in the field of Canadian geology.” 

Billings, E., 1858, On the Asteriadae of the Lower Silurian Rocks of Canada,  Figures and Descriptions of Canadian Organic Remains, Decade III,  at page 34.

Below I’ve provided the plate from Canadian Organic Remains  showing the fossil.



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Sir John William Dawson, who from 1855 to 1893  was professor of geology and principal of McGill University in Montreal, mentioned and relied on Andrew Dickson in a number of publications.   Below I’ve provided quotations from three of his publications.

II.  Fresh-water Shells in the Post-Pliocene Deposits
“... I have been favoured in the past summer, by Andrew Dickson, Esq., with specimens of land and fresh-water shells from the bank of a brook emptying into the Mississippi, a tributary of the Ottawa, two miles below Pakenham Mills. ..  They were found in sand and gravel containing Tellina Greenlandica, and which Mr. Dickson thinks to be undisturbed tertiary deposit.”
...
III.  Land Plants.
“I am indebted to Andrew Dickson, Esq., for the opportunity of studying a large number of nodules containing plants, collected by him at Green's Creek, on the Ottawa.”

Dawson, J. W., 1859, Additional Notes on the Post-Pliocene Deposits of the St. Lawrence Valley; Canadian Naturalist and Geologist. Volume IV, Article III, at pages 36 and 37.

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“In my examinations of these plants [found in the Leda clay at Green’s Creek in Ottawa], I have been permitted to avail myself of the considerable collection in the museum of the geological survey of Canada, and also in the private collections of Mr. Billings, of Prof. Bell at Queen’s College, and of Sheriff Dickson of Kingston.” 

Dawson, J. W., 1868, The Evidence of Fossil Plants as to the Climate of the Post-Pliocene Period in Canada, The Canadian Naturalist and Geologist, New Series, Volume 3 at page 70 

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“Of this nature are the beds at Pakenham, examined by the late Sheriff Dickson, and which I was informed by him, are arranged as follows:
   Sand and surface soil.... 10 feet
   Clay...10 feet
   Fine gray sand (shells of Valvata, &c.)...2 inches
   Clay...1 foot
   Gray sand, laminated (Tellina Greenlandica)...3 inches
   Clay...8 inches
   Light Gray Sand (Valvata, Cyclas, Paludina, Planorbis and Tellina)...10 inches
   Clay...1 foot, 2 inches
   Brown sand and layers of clay (Planorbis and Cyclas)...4 inches

“The fresh water species are peculiar to this locality, and the only marine shell is Tellina Greenlandica, a species now found farther up in our estuaries than most others.
 Mr. Dickson informs me that a similar case occurs near Clarenceville, about four miles from the United States frontier, and at an elevation of about ten feet above lake Champlain. 
... In farther connection with these facts, and in relation also to the question why marine fossils have not been found west of Kingston, Mr. Dickson informs me that fossil capelin are found on the Chaudiere lake... and at Fort Coulonge lake..”

Dawson, Sir J. William, 1893,  The Canadian Ice Age, Being Notes on the Pleistocene Geology of Canada, Montreal, William V. Dawson, at pages 58-59.

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It is also worth noting that  Sheriff Dickson’s fossil collections were relied on by the officers of the Geological Survey of Canada as late as 1905.   Dr. H. M. Ami, Assistant Paleontologist to the Geological Survey of Canada, compiled a list of fossils found within the Perth Sheet in Eastern Ontario, and mentioned:

BLACK RIVER FORMATION
VII Pakenham, Ontario.  Collection of the late Sheriff Dickson
1.  Bythotrephis (Chondrites) succulens, Hall.
2. Stromatocerium rugosum, Hall.
3. Tetradium fibratum, Safford.
4. Columnaria Halli, Nicholson.
5. Orthis tricenaria, Conrad.
6. Actinoceras Bigsbyi, Stokes.

TRENTON FORMATION
IX. Pakenham, Ontario, from the collection of the late Sheriff Dickson

1. Licrophycus  minor, Billings-
2. Solenopora compacta, Billings.
3. Prasopora oculala, Foord.
4. Prasopora lycoperdon, Vanuxem. (= P. Selwyni, Nich.)
5. Agelacrinites Dicksoni, Billings
6. Glyptocrinus ramulosus. Billings.
7. Pleurocystites squamosus, Billings.
8. Lingula quadrata, Eichwald, as of Billings.
9. Lingula riciniformis, Hall
10. Plectambonites sericeus,  Sowerby.
11. Rafinesquina alternata (Conrad), Emmons.
12. Rafinesquina detoidea, Conrad.
13. Dalmanella testudinaria, Dalman.
1 4. Murchisonia bellicincta, Hall.
15.  Fusispira subfusiformis ? Hall.
16.  Orthoceras sp.
17.  Endoceras proliforme, Hall.
18. Asaphus platycephalus, Stokes
19. Calymene senaria, Conrad.
20. Ceraurus  pleurexanthemus, Green.

Ami, H. M., 1904, Preliminary lists of fossil organic remains from the Potsdam, Beekmantown (Calciferous), Chazy, Black River, Trenton, Utica and Pleistocene formations comprised within the Perth Sheet (No. 119) in Eastern Ontario, Geological Survey of Canada, Annual Report for 1901, Volume XIV (New Series), Part J, Report No. 790, at pages 84J-85J.

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Perhaps the greatest praise for Andrew Dickson appeared in an article entitled Elementary Geology that was published in the July, 1855 edition of The Canadian Journal of Industry, Science and Art.   The article talks about the passion for geology in Ottawa and up the Ottawa valley, the Silurian Society that had formed in Ottawa, and the untimely death of Hugh Miller, a self taught Scottish geologist who was held in high esteem in Great Britain.   It continued:

“We do not require to search long or wide for a Canadian Hugh Miller ; one not known to the public by his writings or  published discoveries, but rather by a most honourable mention in the report of the Director of the Canadian Geological Survey; by a unique collection of palaeontological monuments of Silurian age ; by unsurpassed mineralogical proofs of the hidden wealth of the Ottawa valley; by a patient and laborious study of Canadian rocks when a Geological Survey of the country was hardly thought of, and by the fact that many of these investigations were carried on, and fossil and mineral treasures discovered and hoarded up, during years of wild and  romantic life in the uninhabited parts of Canada and the trackless regions of the Hudson's Bay Company's Territory;  trusting to his rod and his gun for the support of life, and, like Hugh Miller, exchanging all day-dreams and amusements  for the kind of life in which men " toil every day that they may be enabled to eat, and eat every day that they may be enabled to toil." With the early progress and development of  the Geology of Canada, the name of Andrew Dickson will always be honorably associated.“

Anonymous, 1855, Elementary Geology, The Canadian Journal of Industry, Science and Art,  1854'5 , Vol. III,  pages 285 - 287 at 286.

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Years after Andrew Dickson’s death, stone from his quarry was used to construct the five span stone bridge at Pakenham, shown below.







The photo is from Library and Archives Canada (MIKAN 3318277) and was taken about 1910 by Augustus L Handford.

Ann P. Sabina (2007) reports that Andrew Dickson’s quarry is now inactive, but that fossils are abundant in Ordovician Black River limestone in the inactive quarry and in rock exposures nearby.   She reports that the fossils include corals, cephalopods, trilobites, brachiopods, bryozoans and cystoids.    She gives the following directions to the quarry: “The Pakenham quarry is on the face of a hill at the east end of the bridge in Pakenham; it is on the east side of Lanark County Road 20 at a point 5.8 km southwest of its junction with Highway 17.”

Sabina, Ann P.  2007,  Rocks and Minerals for the Collector: Ottawa to North Bay and Huntsville, Ontario; Gatineau (Hull) to Waltham and Témiscaming, Quebec. GSC Miscellaneous Report 48

The Ontario Geological Survey lists  two abandoned quarries with the name Pakenham Quarry in the Township of Pakenham.  As the Village of Pakenham falls within lot 11 of concession 11 of Pakenham Township, the  following may be the UTM co-ordinates for Andrew Dickson’s quarry:
Pakenham Quarry
Lot: 11, Concession: 11
UTM Zone: 18
UTM Easting: 399528.012
UTM Northing: 5020897.084

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Christopher Brett
Perth, Lanark County