276 R. Chalmers — Pre- Glacial Decay of Rocks. 



Distribution of the Decayed Rock Materials. 



Pre-glacial beds of decomposed rock, sedentary and strati- 

 fied, have been observed by the writer in Quebec, New Bruns- 

 wick, Nova Scotia, Prince Edward Island and the Magdalen 

 Islands. In some localities the sedentary or indigenous mate- 

 rials occur apparently in extensive sheets ; in others they are 

 detached and local. For the most part they were met with in 

 fragmentary masses, however, having evidently been much 

 denuded before the bowlder-clay was laid down upon them. 

 In a few places in Quebec and in Prince Edward Island, also 

 in the Magdalen Islands, these decomposition products have 

 been partially assorted, and now form thick stratified deposits 

 in river valleys. It is in the bottom of these that gold is found 

 in the Chaudiere valley, and other places in the "Eastern 

 Townships" of Quebec. Similar assorted and re-assorted fluvi- 

 atile deposits, though of greatly reduced thickness, occur in 

 certain parts of Nova Scotia, having been observed along the 

 northern slope and base of the Cobequid Mountains, also in 

 several parts of Prince Edward Island. The Magdalen Islands 

 are non-glaciated, and hence the decayed rock materials there 

 are nearly in the same condition yet as they were in 

 other parts of Eastern Canada previous to the glacial period, 

 forming thick beds which have been slightly assorted by marine 

 action during the Pleistocene submergence. It is in the river 

 valleys of southeastern Quebec as referred to above, that the 

 decomposed materials underwent the greatest transportation 

 and assortment, as will appear by the sections of these beds 

 given on the following pages. 



Wherever these decomposition products occur in seden- 

 tary beds, though mantled by bowlder-clay, the rock surface 

 beneath is without striation from ice. And from the occur- 

 rence of these in so many localities it is evident that a con- 

 siderable extent of rock surface in Eastern Canada has not 

 been scored nor abraded during the glacial period, the ice 

 apparently having slid over the beds which covered it with a 

 sluggish motion, impinging only against the more prominent 

 parts of the solid rock beneath and striating these. 



In the province of Quebec these beds appear, as stated above, 

 to have been least denuded in the hilly broken country lying 

 between the St. Lawrence River and the International bound- 

 ary, the ridges serving as barriers to protect them in many 

 places from denudation by the Pleistocene ice. The compara- 

 tively light erosion of the first glaciation of the Appalachian 

 system, and the mantling of these beds by the bowlder-clay 

 produced by it, preserved them also, to some extent, from the 

 more powerful erosion of the Laurentide ice which followed. 



