No. 5.] NATURAL HISTORY SOCIETY. 28S 



nity of examining the crystalline rocks near Baltimore, and I 

 have also in my notes on the Post-pliocene of Canada, pointed 

 out that in some places, as at Les Eboulements and on the 

 southern side of our own mountain, where the rocks have been 

 sheltered from the northern currents, extensive evidence of old 

 sub-aerial disintegration may be seen. 



It is most instructive to compare in connection with this point 

 the condition of the Silurian rocks on the north-east and south, 

 sides of the Montreal mountain. On the former they show UO' 

 signs of sub-aerial waste, but are polished and striated in the 

 most perfect manner. The striae are N.E. and S.W., or in the 

 direction of the river valley, and that the force producing them 

 acted from the N.E. is shewn by the manner in which projecting, 

 trap dykes are ground on the N. E. side and left rough on the 

 opposite one. The striae vary in direction, having evidently 

 been produced by many successive impacts of heavy bodies mov- 

 ing from the north-east but not always in precisely the sama 

 lines. It seems absolutely impossible that anythiug except, 

 floating ice running from the N. E. or against the present drain- 

 age of the country could have produced these striations,'-^ Oa 

 the limestone slopes which front the mountain, all is different.. 

 In the vicinity of the reservoirs, for example, the coarse earthy 

 limestone, where it has been protected by hard ti-ap dykes, is in 

 many places decomposed to a great depth, and shows no signs of 

 glacial action. 



What does this teach us ? The same truth which we learn, 

 from the wholesale transference of boulders, sand and clay to the 

 south-west over our country, namely, that the great agent im 

 denuding it of all its decomposed and broken rock has been 

 the Arctic current passing over it when submerged. The boulders- 

 which have been swept away from our Laurentian hills are 

 merely the harder and less decomposed parts of rocks which had 

 been disintegrated long before the glacial period, but became the 

 prey of water and ice when the land was submerged. Geolo- 

 gists will not learn to understand fully the Post-pliocene period, 



* I saw last autumn ou St. Helen's Island a very instructive in- 

 stance of striatioa on Utica shale produced by the ice-shove of the- 

 previous spring. This was in the direction of the river valley, but 

 the evidence of the force acting from the south-west was plain, while 

 a miniature moraine of rock fragments in advance of the markings 

 shewed the agent by which they had been effected. 



