R. Chalmers — Pre- Glacial Decay of Rocks. 273 



Art. XXXV. — The Pre- Glacial Decay of Rocks in Eastern 

 Canada;* by Kobert Chalmers, of the Geological Survey 

 of Canada. 



The pre-glacial decay of rocks in glaciated countries is a 

 subject which has not hitherto received much attention from 

 geologists. In North America the chief investigations regard- 

 ing subserial rock decay have been made in regions to the 

 south of the glaciated zone, and but little has been attempted 

 in those portions once occupied by Pleistocene glaciers. The 

 prominence given to the action of these glaciers may have 

 been one of the causes of this neglect or inattention to the 

 products of rock-decomposition. The bowlder-clay and certain 

 gravels and sands overlying it being of considerable thickness, 

 and their origin having apparently been found readily explica- 

 ble from the action of these glaciers, the sedentary beds be- 

 neath, which occur usually in thin and detached sheets in 

 glaciated regions, have thus, to a large extent, been overlooked. 

 That they form a very important member of the superficial 

 deposits, nevertheless, in the glaciated areas of Eastern Canada 

 at least, and one from which the bowlder-clay and all the other 

 overlying stratified deposits have been mainly derived, no geol- 

 ogist will now attempt to deny. 



In the regions of North America to the south of the glaciated 

 belt the beds formed from rock decomposition have been 

 studied, together with the stratified deposits resulting from 

 their modification, by a number of leading geologists. Cham- 

 berlin and Salisbury, McGee, Hilgard and others have investi- 

 gated their character and relation to the later superficial depos- 

 its; while near the limits of the glaciated area, T. Sterry Huntf 

 and PumpellyJ have shown the depths to which this process 

 of decay penetrated and the manner in which the different 

 kinds of rocks have been attacked by it. Russell has treated 

 the question in its wider bearings and given detailed notes and 

 descriptions regarding the chemical and mechanical agencies 

 by which these changes in the rocks are effected ; but his work 

 also appertains to non-glaciated portions only of the United 

 States.§ Prof. Kerr has shown how frost affects the decayed 

 rock materials on slopes and declivities, an action which must 

 be of more potent effect in Canada than in the Southern Appa- 

 lachians.) 



* Paper read in Section C (Geology) British Association for the Advancement 

 of Science, Toronto, August, 1897. 



fThis Journal, vol xxvi, 1883. pp. 190-21:?. etc. 

 t Ibid., 3d series, vol. xvii, 1879, pp. 133-144. 

 § Bulletin U. S. Geological Survey, vol. viii, 1888-89. 

 || This Journal, 3d series, vol. xxi, 1881, pp. 345-358. 

 Am. Jour. Sci.— Fourth Series, Vol. V, No. 28.— April, 1898. 

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