268 GEOLOGY. 



It will be seen from the above analyses of BischofF that Nos. 3 

 and 5, in the quantity of silica and other elements that are present, 

 come very near the Loess of Nebraska. The principal difference 

 is the larger quantity of alumina present in the samples analyzed by 

 BischofF, Chemically the deposits of the Rhine Valley, as Hayden 

 remarks, are not essentially different from those of the Loess soils 

 along the Missouri. 



As would be expected, from the elements which chemical analy- 

 sis shows to be present in these deposits, it forms one of the best 

 soils in the world. In fact, it can never be exhausted until every 

 hill and valley of which it is composed is entirely worn away. 

 Its drainage, which is the best possible, is owing to the remarkably 

 finely comminuted silica of which the bulk of the deposit consists. 

 Where the ground is cultivated the most copious rains percolate 

 through the soil, which, in its lowest depths, retains it like a huge 

 sponge. Even the unbroken prairie absorbs much of the heavy 

 rains that fall. When droughts come the moisture comes up from 

 below by capillary attraction. And when it is considered that the 

 depth to the solid rock ranges generally from five to two hundred 

 feet, it is seen how readily the needs of vegetation are supplied in 

 the driest seasons. This is the main reason why over all the re- 

 gion where these deposits prevail the natural vegetation and the 

 well-cultivated crops are rarely dried out or drowned out. I have 

 frequently observed a few showers to fall in April, and then little 

 more rain until June, when, as will be considered farther on, there 

 is generally a rainy season of from three to eight weeks' continuance. 

 After these June rains little more would fall till autumn; and yet, if 

 there was a deep and thorough cultivation, the crops of corn, ce- 

 reals and grass would be most abundant. This condition represents 

 the dry seasons. On the other hand, the extremely wet seasons 

 only damage the crops over the low bottoms, subject to overflow. 

 Owing to the silicious nature of the soils they never bake when 

 plowed in a wet condition, and a day after heavy rains the plow can 

 again be successfully and safely used. 



The physical properties of the Loess deposits are also remarka- 

 ble. In the interior, away from the Missouri, hundreds of miles of 

 these Loess deposits are almost level or gently rolling. Not un- 

 frequently a region will be reached where, for a few miles, the 

 country is bluffy or hilly, and then as much almost entirely level, 

 with intermediate forms. The bluffs that border the flood-plains of 



