260 GEOLOGY. 



gravels and sometimes sands, very distinct from the Pliocene sands 

 of the Niobrara. The Loess deposits to be described hereafter 

 abut against them, but often their tops have been blown over the 

 Loess to such an extent that even geologists have been deceived in- 

 to the belief that they are of very recent origin. They, however, 

 antedate the Loess, as is evident from the fact that they extend be- 

 neath the latter. I am not sure whether any of them exhibit any 

 true marks of stratification. They bear some resemblance to the 

 Karnes of Scotland and Asars of Scandinavia, and to them they 

 are for the present referred, though doubtfully. Though their up- 

 per portions are composed of sands, they often shade down into 

 fine and then coarse gravels. This is specially true in southwest 

 Nebraska, where at long intervals canyons are found which par- 

 tially cut through them. 



Calcareous and Silicious Materials. — Between the deposits which 

 are doubtfully referred to the Karnes, and lying on their flanks, oc- 

 our, in many places, great beds of fine silicious matter, which in 

 places is calcareous to a greater or less degree, and is especially 

 rich in iron, mostly in the form of a sesquioxide. It is often mis- 

 taken for Loess, whose character it often approaches. The best ex- 

 amples of it are seen in the Republican Valley, from Harlan 

 County westward, where the line of junction between it and the 

 overlying Loess is sharply outlined, and is exposed for thirty miles. 

 Its color is a darker reddish brown than Loess. Under the micro- 

 scope, the silicious materials appear coarser than the Loess, with 

 the addition, occasionally, of small water-worn pebbles. It also 

 varies much more in character. The following analysis, only par- 

 tially completed, indicates its chemical character: 



Insoluble (silicious) matter 78 . 10 



Ferric oxide 5.98 



Alumina * 2 .70 



Lime carbonate 11.01 



Lime phosphate, undetermined. 

 Magnesia cirbonate, u 

 Potassa, " 



Soda, " 



At other points in Nebraska this reddish brown silicious matter 

 shades insensibly into the overlying Loess. Such examples can be 

 seen along the Missouri River from Plattsmouth to the south line 

 of the State. Along this same route beds of almost pure sand oc- 



