62 THE ICE AGE IN CANADA. 



that of ice. I am sure that this is the case with many of 

 the indentations of the coast of Nova Scotia, which are 

 cut into the softer and more shattered bands of rock, 

 and show, in raised beaches and gravel ridges like those 

 of the present coast, the levels of the sea at the time of 

 their formation." 



To the period of the boulder-clay we may refer those 

 ridges and pavements of boulders imbedded in this clay 

 or continuous with it, and which testify to the carrying 

 and packing power of ice. We shall find, however, that 

 such moraine-like ridges are not confined to this period, 

 but occur along the sea-margins of the Later Pleistocene, 

 and are even at this day in process of formation on a 

 considerable scale along the borders of the St. Lawrence. 



2. — The Leda Clay. 



This deposit constitutes the subsoil over a large portion 

 of the great plain of Lower Canada, varying in thickness 

 from a few feet to 50 or perhaps even 100 feet, and 

 usually resting on the boulder-clay, into which it some- 

 times appears to graduate, the material of the Leda clay 

 being of the same nature with the finer portion of the 

 paste of the boulder-clay. Its name is derived from the 

 presence in it of shells of Leda glacialis, often to the 

 exclusion of other fossils, and usually in a perfect state, 

 with both valves united. 



The typical Leda clay in its recent state is usually gray 

 in colour, unctuous, and slightly calcareous. Some beds, 

 however, are of a reddish hue ; and in thick sections 

 recently cut, it can be seen to present layers of different 

 shades and occasional thin sandy bands, as well as layers 

 studded with small stones. It sometimes holds hard 

 calcareous concretions, which, as at Green's creek on the 



