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,
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