14 STRATIGRAPHICAL GEOLOGY. 



retical grounds, the whole of the Huronian series from southern Massa- 

 chusetts to Gaspe, dividing it into the Levis, Lauzon, and Sillery forma- 

 tions. He supposes the latter assemblage has been metamorphosed so as 

 to lose its original mineralogical character. The two sets of beds may 

 often be distinguished by the presence or absence of fossils, the Huro- 

 nian being usually destitute of any decided evidences of life. The Quebec 

 rocks are associated with the preceding group, also, in northern New- 

 foundland, attaining a thickness of 6600 feet. 



Next in order are the Chazy, La Motte or Black River, and Birdseye 

 limestones, not usually much over 150 feet thick, and, so far as known, 

 confined to the Champlain and Upper St. Lawrence valleys. 



The Trenton limestone is one of the most characteristic of the Lower 

 Silurian formations. In Quebec and New York the maximum thickness 

 is 600 feet. It may be represented by the lower limestones of Anticosti 

 island ; at least, more than 1 200 feet thickness is referred to the Tren- 

 ton and Lorraine scries combined. 



The Utica slate is rather a local deposit, estimated at 300 feet along 

 the Champlain and St. Lawrence valleys. It passes into the Lorraine 

 shales, or Hudson River group, which everywhere accompanies the Utica 

 formation. Logan says it must be 2000 feet thick in Canada. These 

 shales in New York are the equivalents of limestones in Ohio, etc., just as 

 seems to be the case in Quebec and Anticosti. 



Two interesting conclusions may be derived from this summary of the 

 Cambrian and Silurian of the St. Lawrence valley: first, the thickness 

 uniformly increases in passing north-easterly ; secondly, slaty, sandy, 

 and siliceous rocks occasionally change into limestones. Both these feat- 

 ures are explicable upon the theory of the deepening of the ancient ocean 

 north-easterly, the slates increasing in deeper water, and the sea-beaches 

 corresponding to calcareous accumulations out at sea. 



The Upper Silurian groups are sparingly represented in the St. Law- 

 rence valley. There is nothing of this age west of Montreal, in the area 

 of the map. St. Helen's island, in the river opposite Montreal, belongs 

 to the Lower Helderberg. Farther east are considerable masses of red 

 shale, occupying at least three outliers, which are referred by Logan to 

 the Medina period. Near the end of the Gaspe peninsula are 2000 feet 

 of limestones, apparently a great development of the Lower Helderberg. 



