it.] CANADIAN EXTENSION. 117 



tologist of the survey, decided that the rocks there and those which had 

 beeu associated with them by Sir William E. Logan belonged at the 

 base of the Lower Silurian and not at the summit, as had hitherto been 

 held. These conclusions were announced by Logan in a letter to Mons. 

 J. Barrande published in I860. 1 In this letter the whole Quebec group, 

 from the base of the maguesian conglomerate with their accompanying 

 maguesiau shales, to the summit of the Sillery sandstone, is stated to 

 have a thickness of perhaps from five to seven thousand feet. It ap- 

 pears to be a great development of strata at about the horizon of the 

 Chazyand Calciferous of the New York section. 



He says he is not prepared to state that a typical form of the Pots- 

 dam sandstone is present where the shales are in greatest force. 



Neither am I prepared to assert its absence, as there are in some places masses of 

 granular qnartzite, not far removed from the magnesiau rocks of the Quebec group, 

 which require farther investigation; but, from finding wind-mark and ripple-mark 

 on closely succeeding layers of the Potsdam sandstone where it rests immediately 

 upon the Laurentian series, we know that this arenaceous portion of the formation 

 must have been deposited immediately contiguous to the coast of the ancient Silurian 

 i. where part of it was even exposed at the ebb of tide. Out in deep water the de- 

 posit may have been a black, partially calcareous mud, such as would give the shales 

 and limestones which come from beneath the Quebec group. 



In Canada no fossils have yet been found in these shales, but the shales resemble 

 those in which Oleni have been found in Georgia (Vermont). These shales appearto 

 be interposed between eastward dipping rocks equivalent to the magnesiau strata of 

 the Quebec group, and they maybe brought up by an overlapping anticlinal or dis- 



cation. We are thus led to believe that these shales and limestones, which may be 

 subordinate to the Potsdam formation, will represent the true Primordial zone in 

 Canada. - 



In 1863 Sir Win. E. Logan published his great resume' of the work 

 done by the Geological Survey of Canada from its commencement to 

 1S03. 3 He describes the northward extension of the Georgia series 

 and Red Saudrock of Vermont into Canada, stating that they had been 

 traced but a short distance when they become faulted out and replaced 

 by a later formation. 4 



The Sillery shales and sandstones, as well as the conglomerate beds 

 of Point Levis, Quebec, are described in detail and assigned to about the 

 horizon of the Calciferous-Chazy formations of the New York section. 

 The Levis and Sillery formations are referred to the Quebec group, and 

 the latter series is traced south westward along the western base of the 

 Sutton Mountain range. The Levis formation is divided into seventeen 

 parts, consisting of alternating calcareous shales, argillaceous shales, 

 limestone conglomerate, and gray sandstone. The upper beds consist of 



1 Logan, W. E. Remarks on the fauna of the Quebec group of rocks and tbe Primordial zone of C.m- 

 ada. Canadian Naturalist, vol. 5. 1860, p. 475; vol. G, 1861, pp. 106-120 ; Am. Jour. Sci.. 2d ser., vol. 31, 1861, 

 pp. 216-220. Remarques sur la fan no des roches du groupe de Qu6bec et sur la zone primordiale du 

 Canada, Soc. geol. France, Bull., 2 e ser., vol. 18, 1861, pp. 309-314. 



•Am. Jour. Sci., 2d ser., vol. 31, p. 219. 



s Geological Survey of Cauada. Report of progress from its commencement to 1863. Montreal, 1803, 

 pp.983. 



4 Op.cit, p. 285. 



