SOME LOCAL DETAILS. 197 



In this section the greater part of the tliickness corres- 

 ponds to the Leda clay, which at this place is thinner and 

 more fossiliferous than usual Along the south-east side 

 of the Mountain, and in the city of Montreal, the beds 

 have been exposed in a great number of places, and are in 

 the aggregate at least 100 feet thick, though the thickness 

 is evidently very variable. The succession may be stated 

 as follows : 



1. Saxicava Sand. — Fine uniformly grained yellowish and 



gray silicious sand with occasional beds of gravel in 

 some places, and a few large Laurentian boulders, 

 Saxicava, Mytilns, &c., in the lower part. Thickness 

 variable, in some places 10 feet or more. 



2. Leda Clay. — Unctuous gray and reddish calcareous clay, 



which can be observed to be arranged in layers 

 varying slightly in colour and texture. Some of 

 these layers have sandy partings in which are 

 usually Foraminifera and shells or fragments of 

 shells. In the clay itself the only shells usually 

 found are Leda arctica and a smooth deep-water 

 form of Tellina Grcenlandica ; but toward the 

 surface of the clay, in places where it has not been 

 denuded before the deposition of the overlying sand, 

 there are many species of marine shells. A few 

 large boulders are scattered through the Leda clay. 



3. Boidder-day. — Stiff gray stony clay, or till, with large 



boulders and many glaciated stones, often of the same 

 Trenton rocks which occur on the flanks of the 

 mountain. It is of great thickness, though it has been 

 much denuded in places, and has not been observed 

 to contain fossils. It is especially thick at the south 

 and south-west sides of the Montreal mountain. 



