282 B. Chalmers — Pre- Glacial Decay of Rocks. 



the same in both regions, but for the reasons stated they may 

 never have been as deep in the glaciated zone. The facts 

 would seem to point to the conclusion, however, that rock- 

 decay has been in progress in this country for long ages, proba- 

 bly as long as in southern climates, although somewhat irregu- 

 lar and intermittent in its operations. 



From the extent and depth of the sedentary and assorted 

 beds found beneath the bowlder-clay it may be inferred that 

 the Pleistocene glaciers were not as heavy, or of such erosive 

 power, as many geologists have supposed. This has been the 

 case especially in the flat districts of the Maritime provinces 

 occupied with Carboniferous rocks. In these districts the ice 

 has been of a less vigorous and sweeping character than in the 

 more elevated parts of the country, and was apparently slug- 

 gish in movement, passing over the loose deposits and rock 

 surfaces without eroding them deeply. Only from certain low 

 ridges, or from the brows of hills exposed to the full force of 

 the grinding ice masses, have the decomposition products been 

 wholly removed and the surfaces of the solid rocks beneath 

 scored and laid bare. 



The general aspect of the dry land in Eastern Canada before 

 the advent of the glacial period must have been closely similar 

 to that of the country to the south of the glaciated area. The 

 greater denudation it has suffered since from subserial and 

 glacial agencies and the filling up of the valleys, partially or 

 wholly with the bowlder-clay, thus levelling and reducing the 

 inequalities of the surface, have largely modified, in some 

 places entirely changed, the appearance. But amid all the 

 vicissitudes of climate and oscillations of level which the 

 region underwent, and the denudation to which the surface has 

 been subjected, these products of rock-decay, representing the 

 subaerial action of long ages, have thus been preserved in rem- 

 nants and detached sheets, the recognition of which unfolds 

 another episode in the geological history of Eastern Canada 

 hitherto overlooked, and adds new interest to the study of its 

 superficial deposits. 



Geological Survey Office, Ottawa, May, 1897. 



