38 THE CANADIAN NATURALIST. [Vol. vi. 



ing upwards into pure sand. In this last case the lower part of 

 the sand at its junction with the clay is often very rich in fossils, 

 showing that after the deposition of the clay a time of quiescence 

 supervened with favourable conditions for the existence of marine 

 animals, before the sand was deposited. It is usually, indeed, in 

 this position that the greater part of the shells of our Post-plio- 

 cene beds occur ; the Saxicava sand being generally somewhat 

 barren, or containing only a few shallow-water species, while the 

 Leda clay is usually also somewhat scantily supplied with shells, 

 except toward its upper layers. Hence it is somewhat difficult to 

 refer a large part of the shells to either deposit, I have however 

 usually regarded the richly fossiliferous deposit as belonging to the 

 Leda clay ; and where, as sometimes happens, the clay itself is 

 absent and merely a thin layer rich in fossils separates the Saxicava 

 sand from the Boulder-clay, I have regarded this layer as the re- 

 presentative of the Leda clay. 



The Siixicava sand, in typical localities, consists of yellow or 

 brownish quartzose sand, derived probably from the waste of the 

 Potsdam sandstone and Laurentian gneiss, and stratified. It 

 often contains layers of gravel, and sometimes is represented alto- 

 gether by coarse gravels. It is somewhat irregular in its distri- 

 bution, forming banks and mounds, partly no doubt in consequence 

 of original irregularities of deposit, and partly from subsequent 

 denudation. In some outlying localities it is liable to be con- 

 founded with the modern river sands and gravels. Large trav- 

 elled boulders often occur in it ; but it rarely contains glaciated 

 stones, the stones and pebbles seen in it being usually well 

 rounded. 



From the nature of the Saxicava sand, it is obvious that it 

 must be a shallow water deposit, belonging to the period of emer- 

 gence of the land ; and it must have been originally a marginal 

 and bank deposit, depending much for its distribution on the 

 movement of tides and currents. In some instances, as at Cote 

 des Neio-es, near Montreal, and on the Terraces on the Lower St. 

 Lawrence, it is obviously merely a shore sand and gravel, like 

 that of the modern beach. Ridges of Saxicava sand and gravel 

 have often been mistaken for moraines of glaciers ; but they can 

 generally be distinguished by their stratified character and the 

 occasional presence of animal remains, as well as by the water- 

 worn rather than glaciated appearance of their stones and 

 pebbles. 



