322 THE BEGOLITH 



Although comprising the soil of almost the entire region that 

 was but recently known as the Great American Desert, it needs 

 but water to make it laugh with harvests. While its physical 

 properties undoubtedly have much to do with its fertility, this 

 quality must also be in part due to the fresh and undeeomposed 

 condition of its constituent parts. Originating doubtless by 

 purely mechanical agencies, it has been swept by winds and 

 spasmodic rains into closely adjacent basins occupied by but 

 temporary lakes, where, spread out over a floor sometimes almost 

 absolutely level, it has been subjected to a minimum amount of 

 leaching and retains until to-day its youthful strength and 

 powers of recuperation.^ The analyses given on p. 321 will 

 serve to show the varying character of the deposits included 

 under this name. Especial attention need be called only to 

 the relatively high percentages of lime and the alkalies. 



Ghamplain Clays. — Under the head of alluvial deposits must 

 also be considered those clay accumulations which result from 

 the deposition of fine aluminous sediments sorted by running 

 streams from glacial debris and like the loess laid down in quiet 

 water, though usually estuarian rather than lacustrine. These 

 are the well-known Leda or Ghamplain clays ^ of glacial regions, 

 which on genetic grounds might well be classed as aqueo-glacial 

 deposits. 



Such are very abundant along all the lower valleys of the 

 principal rivers of New England, sometimes coming to the im^ 

 mediate surface or overlaid with a thin layer of sandy material 

 which^ together with a little organic matter, forms the true soil. 

 They form, according to Dawson,^ the sub-soils over a large part 

 of the great plains of Lower Canada, varying in thickness up 

 to 50 or even 100 feet, usually resting upon the boulder clay. 

 They are, as a rule, of almost impalpable fineness, unctuous, and 

 extremely plastic. Excepting where superficially oxidized to 

 buff or brown, they are of a blue-gray color and may show on 

 analysis considerable quantities of lime carbonate and alkalies, 

 features whereby they are readily distinguished from the resid- 

 ual clays, and which are regarded as indicative of an origin by 

 mechanical rather than chemical means. When dried, they be- 

 come greatly indurated, and when unmixed with other mate- 

 rials, bake so hard during seasons of drought, or are so plastic 



* See further on p. 357. 



2 So called from their most characteristic fossil, Leda. 



3 The Canadian Ice Age. 



