ACTION or WATEB AND ICE 279 



of the individual particles being of course dependent upon that 

 of the moraines from which they are derived. 



The effects upon the landscapes of this ice sheet have been 

 lasting and peculiar. One may safely imagine that, before its 

 invasion, the surface was covered with decayed and softened 

 materials like the residual soils of the Southern states, which 

 had been cut up into valleys and intervening ridges by the 

 stream of that time. The ice stripped from these surfaces 

 their mantle of decomposed materials, and in addition cut into 

 the fresh rock, actually planing the entire country so deeply that 

 the preglacial surface is no longer recognizable. The hills were 

 thus lowered and the valleys deepened or again filled by sand 

 and gravel. On its final retreat the surface, in many instances, 

 was left so thickly strewn with boulders that cultivation was 

 well nigh impossible prior to their renewal. The stone walls of 

 the New England farms were built not more for barriers against 

 roving cattle than to rid the fields of their material. (See 

 Fig. 2, PL 28.) 



The direction taken by this drift material was quite variable. 

 It was, as a rule, from the north toward the south, with many 

 minor deflections. Boulders of Laurentian rocks north of Lake 

 Huron are abundant in the drift about Oberlin, Ohio, and even 

 further south. Boulders of native copper from the Lake Su- 

 perior region are found even as far south as Kankakee, Illinois, 

 and a large boulder of a peculiar conglomerate known in place 

 only near Ontario, has been found a few miles south of the 

 Ohio River in Kentucky. Dawson states ''that boulders from 

 the Laurentian axis of the continent, which stretches from 

 Lake Superior northward to the west of Hudson Bay, have 

 been transported westward a distance of 700 miles, and left 

 upon the flanks of the Rocky Mountains at an elevation of 

 something over 4000 feet."^ 



All over the states once occupied by this ice sheet the ma- 

 terial originating from the decomposition of rocks in situ^ or 

 deposited on alluvial plains, was, with a few minor exceptions, 

 carried away to the southward and in part dumped into the 

 Atlantic, while its place was supplied by mongrel hordes from 

 the north. In process of digging for the foundations of the 

 Experiment Station at Orono, Maine, the fresh and highly 

 polished slaty rock was found but a few feet below the sur- 



^ Ice -Age in Nortli America, p. 171. 



