296 



GEOLOGY. 



matter. The following analyses of these soils will give a better 

 idea of their physical character. The samples were taken from 

 what are believed to be average soils. The first is from the Elk- 

 iiorn, the second from the Platte, the third from the Republican, 

 and the fourth from the Blue River. The fifth is from an excep- 

 tionally wet and sticky soil, about two miles southeast of Dakota 

 City. 



It is well known that many soils vary a great deal in chemical 

 properties that are taken only a few feet apart, and therefore anal- 

 yses often fail to give a correct idea of their true character. But 

 from the above analyses, taken from widely distant localities, it is 

 at least evident that chemically, alluvium differs from the Loess de- 

 posits principally in having more organic matter than alumina, and 

 less silica. The depth of the alluvium varies greatly. Occasionally 

 sand and drift materials predominate in the river bottoms, especially 

 in the subsoil; sometimes the alluvium is of unknown depth, and 

 again in a few feet the drift pebbles and sand of the subsoil are 

 struck. This is especially the case in some of the western valleys 

 which were worn down to the drift, and were not again subse- 

 qently filled up, though such cases are not often met with. There 

 must have been a period of longer or shorter duration, when the 

 bottoms were in the condition of swamps and bogs; and during this 

 period the greater part of that organic matter, which is a distinguish- 

 ing feature of these lands, accumulated in the surface-soil. It would 

 be easy to select isolated spots, where the soil has forty per cent of 

 organic matter; where, in fact, it is composed of semi-peat. When 

 we reflect that this black soil is often twenty feet thick, it is appar- 



