ROCKS OF THE ATLANTIC COAST OP CANADA, ETC. 809 



It will be observed here that the Graptolitic faunas referred to by 

 Lapworth extend from the Tremadoc to the Caradoc inclusive ; but 

 the Quebec group proper may be regarded as limited by these groups 

 above and below. 



It is also to be observed that the Quebec group conditions of 

 shale- and sandstone-deposit with cold-water animal species seem, 

 in the later Trenton and Utica periods, to have become prevalent 

 over the interior plateau as well as the marginal area. 



This appears not only from the wide extension of the Grapto- 

 litic fauna over all the plateau west of the Appalachians in this 

 later Ordovician time, but from the occurrence of these fossils in the 

 extreme west. Graptolites of this age are reported by White in 

 Nevada *, and have recently been found by M^'Connell and identified 

 by Lapworth in the Wapta Pass in the Rocky Mountains of Canada f. 

 Thus, what we have regarded as marginal and submarginal con- 

 ditions may in the later Ordovician have prevailed from the Atlantic 

 to the Pacific. This was undoubtedly a consequence of the gradual 

 subsidence going on in the Ordovician age. It was naturally fol- 

 lowed by the settlement of the ocean-bed, which raised again the 

 continental area and folded the marginal and submarginal Ordovician 

 rocks on both sides of the Atlantic. 



I may add that the above views correspond closely with those I 

 have held for many years, as the result of much study of these rocks 

 in my summer vacations on the Lower St. Lawrence, and which are 

 thus expressed in a paper published in 1883 + : — 



" There seems reason to believe from Mr. Richardson's recent 

 observations that Graptolitic zones reaching from the Lower Tre- 

 madoc to the Upper Llandeilo may be discriminated in the great 

 mass of sediments known as the ' Quebec Group,' which the writer 

 has long believed, on the evidence of the fossils he has himself 

 observed, to represent a lapse of geological time extending from the 

 base of the Potsdam to the Chazy limestone." Prof. Lapworth's 

 recent memoir extends the range of this comparison as far upward 

 as the Trenton and even the Utica. 



One feature of the Quebec Series is especiall^^ characteristic and 

 American ; this is the great limestone-conglomerates, which form 

 conspicuous features in its middle portion. These conglomerates, 

 which are very irregular in their distribution, and swell out rapidly 

 to great thickness, degenerating as rapidly to mere sandstones, are 

 remarkable for the quantity of boulders and pebbles of limestone 

 which they contain, and which often afford Cambrian fossils, though 

 in other cases they appear to belong to the limestone of the lower 

 part of the Quebec group itself. The only means of explaining 

 these conglomerates seems to be the action of the coast ice, which 

 at this period appears to have been as energetic on the American 

 shores as at the present day, and seems to have had great reefs of 

 limestone, probably in the area of the Gulf of St. Lawrence, to act 



* Eeport on the 100th Meridian, vol. iv. 



t "Eeport on Rocky Mountains," Geol. Surv. of Canada, 1887. 



J Report on Peter Redpath Museum. 



