ROCKS OF THE ATLANTIC COAST OF CANADA, ETC. 807 



Before leaving the Cambrian, it ma}' be well to state that Mr. 

 Matthew informs me that he hopes to make out in the St. John series 

 the equivalents of all of the subdivisions of the Farado.vides-zone 

 established by Linnarsson in Sweden, so that there would seem to be 

 a correspondence even in the minor details of the deposits on the 

 opposite sides of the Atlantic *. This, as we shall see, also appears 

 to Prof. Lapworth to hold in the case of the Graptolitic fauna of the 

 Upper Cambrian and Ordovician on the two Atlantic margins. 



ly. The Ordovician System. 



With the incoming of this new age a more marked distinction 

 occurs in America between the marginal and plateau-deposits. I 

 have already referred to this in the Calciferous ; but it is more dis- 

 tinct as between the marginal and submarginal areas and those 

 inland, in the period on which we now enter. 



In Newfoundland, Murray and Howley have described large areas 

 of Quebec-group rocks in the west and north of the island which 

 seem to be continuations of the submarginal area of the Lower St. 

 Lawrence. There is also one limited exposure of Trenton Limestone 

 on the west coast, and belonging to the area of the Gulf of St. 

 Lawrence, the peculiar conditions of which I have already mentioned. 

 In Nova Scotia we have as yet no representatives of the Ordovician 

 system except slates associated with igneous rocks, resembling in 

 mineral character the Borrowdale series of the North of England, 

 and destitute of fossils. In northern New Brunswick we find a belt 

 of slaty beds representing the Quebec group of Logan, which is the 

 characteristic form of the submarginal development of this system 

 occupying the St. Lawrence valley. This group, resembling in many 

 respects the Arenig of England, and consisting principally of slates, 

 sandstones, and conglomerates, constitutes the eastern representative 

 of the great Upper Calciferous and Chazy Limestones widely spread 

 over the internal plateau, and probably of part of the Trenton as well. 



The origin of this formation and its true relations to the interior 

 plateau-deposits were early defined by Logan, who regarded the 

 Quebec group as an Atlantic deposit thrown down in the open sea 

 along the margin of the old Laurentian plateau, while thinner and 

 differently constituted beds were being formed in the shallower and 

 warmer waters of the plateau itself. It was further found and illus- 

 trated by Logan that in the great earth-movements which closed the 

 Ordovician period these marginal and submarginal deposits had been 

 crushed and folded against the old Laurentian border, and even, 

 in places, pushed over the inland formations by reversed faults, while 

 the latter remained comparatively undisturbed. These peculiar 

 arrangements, which extend southward along the Appalachian 

 ranges, led to much discussion among the geologists of the New York 

 Survey, and to that " Taconic " controversy which is still scarcely 

 terminated. 



So far as our present subject is concerned, it is sufficient to 



* Amer. Jonrn. of Science, May 1887. 



