MINERALS AND GEOLOGY OF CANADA. 205 
considerable developement. Exposures occur at Montreal, and in 
the vicinity of that city, where the shales are much penetrated by 
trap dykes ; also on the Richelieu River, and in the adjoining dis- 
trict ; here and there on the north shore of the St. Lawrence, between 
Montreal and Quebec, as‘on the St. Maurice and Achigon rivers ; 
largely in the vicinity of Quebec itself, and more especially about 
Beauport and the Falls of Montmorenci, and along the north shore 
of the Island of Orleans; again near Cape Tourmente; and at Lake 
St. John on the Saguenay. 
The Hudson River Formation.—The strata of this sub-division in 
Western Canada, consist essentially of arenaceous shales. These 
are chiefly of a bluish or greenish-grey colour, but become brown by 
weathering. They are occasionally interstratified with layers of 
ordinary sandstone, and with a few beds of limestone—their extreme 
thickness being about 700 feet. In Hastern Canada, the formation 
consists also in chief part of shales of a similar character, mixed with 
subordinate beds of bituminous shale, conglomerate, and limestone. 
Its thickness in the vicinity of Quebec is estimated at about 2000 
feet ; but in Western Canada, it does not exceed 700 or 750 feet in 
thickness. Many of its fossils are identical with those of the Tren- 
ton and Utica groups; but certain forms are peculiar to it; and 
others (such as ambonychia radiata, modiolopsis modiolaris, &§c.) 
although occasionally occurring in the Trenton group, are more par- 
ticularly characteristic of the present formation. The accompanying 
figures represent some of the most important of these fossilized re- 
mains. 
’ Fig. 202.—Grapto- Fig. 203.—G. ramosus (Hall.) Fig. 204.—Lepteena seris 
aes A ites cea (Sowerby-) 
all, 
