of the St. Francis Y alley, Quebec. 



75 



rocks. The part of the dolomite, " B," immediately surrounding 

 the locality of the fossils, and the intervening mica schists are 

 accordingly colored Trenton in Lots 13, 14 and 15 in Ranges 

 xii and xiii, while they, " B-B,' ? are elsewhere mapped as Pre- 

 cambrian in either direction along the strike. 



The order of deposition which best explains the structural 

 features appears to be as follows, in ascending series : 



A. limestone, Trenton or Black Eiver 



B. mica schist j mapped as Precambrian 



C. dolomite f except within the line D-D' 

 F. fossils 



y. strike and dip — 40°. 



1. Black limestone, with black mica schist as its marginal 

 or shallow-water equivalent. 



2. Qnartzite, quartzose and micaceous dolomite, which were 

 chiefly deposited in the northern part of the section and barely 

 extend to the northern side of the present exposure of the 

 black limestone. 



3. Gray or green mica schists covered the entire trough 

 between the preexisting igneous ridges. 



Two causes present themselves to account for the real or 

 apparent greater thickness of these schists towards the north. 

 If, as the position of the locality with reference to the main 

 ridges of the Appalachian uplift indicates, the Lower Silurian 

 transgression come from the north, the original thickness prob- 

 ably was really greater in the northern than in the southern 

 part of the section. Or, since all these elastics after their 



