THK SUt'CE.SSIOX OF DEPOSITS. 5," 



(Tdsscs the ^l. l.awrt'iK'c, and wlicrc tlic same ancient 

 r(X'ks cross tlu- Ottawa: and in general tlie Leda clay 

 may be said to lie limited to the lower Silurian plain, and 

 not to mount up the Laurentian and metamori)hic hills 

 l)(aiiidin,Li,' il. Since, howcNcr, the le\el of the water, as 

 indicated hy the ti'rraces in Lower Canada, and hy the 

 jirohalih' dejilh at which llie Ledii clay was de]»osited, 

 would cany the sea le\el far lieyond the limits al)o\G 

 indicated, ami even to the liase of the Niagara escarp- 

 ment, we must su[)])ose, either — (I) that the supply of 

 this sediment failed toward the west; or ('2) that tlie 

 mud has heeii removed l>y tU'iiudation or worked over 

 again by the fresh waters so as to lose its marine fossils: 

 or (3) that tlu; relative levels of the western or eastern 

 parts of Canada were difterent from those at ]iresent ; or 

 (4) that tlu^ water uiay have l)eeii freshened and rendered 

 cold by the influx of luelling snow and ice into a landlocked 

 water area or one with a nanow oi)ening. As already 

 stated, there are indications that the first may be an 

 element in the cause. The second is no doubt true of the 

 clays which lie in the immediate vicinity of the lake 

 basins. Dr. Sjieneer has detailed many ol)ser\'ations in 

 favour of the third, more especially in the later glacial 

 and I'ost-glacial periods. 



I believe, however, that nmeh more rigorous investiga- 

 tions of the claA'S of western Canada are re([uired before 

 we can certainly ahirm that none of them hold marine 

 fossils.* 



Whittlesey has doseril)ed the western drift depo.sits in 

 the Smithsonion Contributions, Vol. XV., and according 



* It 's to be observed that even neai- the coast the gi-eater part of 

 the thickness of tlie Leila clay is often unfossiliferous. 



