48 



THK UK A(iK IN CANADA. 



plains iiikI clcvatidii of inoimlains. There is reason [n 

 liclievo that such altei'uations were imL iiit'retiuenl in the 

 IMeistoei'iie, and that t heii' oeenrrenee will e.\|>lain many 

 of tlu' e()ni]»lexities nf these (je|M)sils. 



If we adopt for the more general di'posils t.lie hypothesis 

 of float ine,' ice, we ninst l)e prejiai'ed to consider in con- 

 neelion with this sul»ject a snhsidence so yreat as to place 

 atone period all hiit the highest |iarts of the I^aurentides 

 and Ai)i»alachians undt'r \vat<'r. in this case a vast 

 vohune of aiclic ice and water wonld ponr oNcr the 

 country (tf the ^reat lakes to the S.W., while any ohstrue- 

 tion occuiring to the south would throw lateral currents 

 over the A])j)alachians to the eastward. 



It is evident from the descriptions of Smith, ( ieikie, 

 .fanieson, Crosskey, and olhei's, that the houlder-clay 

 of Scotland and Scandina\ia coi'responds precisely in 

 character with that of Canada, and there, as in Aniei'ica, 

 the theory of a continental i^lacier has heen resoiled to 

 for its explanation. The ohjeetious to this hypothesis are 

 very al)Iy stated hy Mi'. Milne IIouk; in a ])ai)ei' on the 

 " IJoulder-clay of JMirope," in the Transactions of the 

 lioyal Societv of Kdinhuriih, ISO!). 



To this ])eriod and these causes must also he assiifued 

 the excavation of the liasius of the ,t;reat American lakes. 

 These have heen cut out of the softer memhers of the 

 Silurian and l)e\dnian Formations: ])Ut the mode of this 

 excavation has l)een re<i;arded as \ery mysterious : and, 

 like other mysteries, has l»een referred to glacier.s. Its 

 real cause was ol)viously river and atmosi)heric erosion in 

 the riiocene jieriod, sui)i»lemented by the Howing of cold 

 ocean currents over the American land durinjj; its sub- 

 mergence.* The lake-basins are thus of the same nature 



See Chapter III. 



