GEOLOGY. 269 



absorption is generally in proportion to the amount of geine 

 and the lightness of the soil.* 



" This is an important item to the cultivator. Lands pos- 

 sessing this power in a considerable degree readily absorb 

 the dew in dry weather ; and, in Avet weather, do not suffer 

 the superfluous rain to accumulate on the surface. 



" A striking feature in the character of the Iowa and Wis- 

 consin soils, as the table shows, is the entire absence, in 

 most of the specimens, of clay, and the large proportion of 

 silex. This silex, howxver, does not commonly show itself 

 here in its usual form — that of a quartzose sand. It appears 

 as a fine, almost impalpable, siliceous powder, frequently 

 occurring in concreted lumps that resemble clay ; and, 

 indeed, it was often reported to me incorrectly as clay — an 

 error ultimately detected by analysis. 



" This almost impalpable powder, the chief constituent and 

 almost sole residuum of the Iowa and Wisconsin soils, is so 

 highly comminuted, that, when examined under the micro- 

 scope, for the most part, its atoms present no crystalline or 

 even granular appearance. 



" This fine siliceous residuum, after being boiled with 

 strong aqua regia, lost but 10 per cent. ; of which but 5 per 

 cent, was alumina. 



" This absence of any material per-centage of clay in the 

 soils under consideration prevents the rolling lands from 

 washing away ; and it imparts to the streams a crystal clear- 

 ness, which even after heavy rains is hardly disturbed. The 

 appearance of these transparent rivulets flowing over a soil, 



" * ' In general, the more finely the parts of a soil are divided, the better 

 they absorb water.' — Chaptal. 



" This applies particularly, as the sequel will show, to the soils in 

 question." 



