266 GEOLOGY. 



miles ranges from forty to ninety feet. South of Kearney, and for 

 a great distance west, along the Union Pacific Railroad as far as to 

 the Republican, there is a great expanse of territory covered by a 

 great thickness of this deposit. I measured many sections in wells 

 over this region, and seldom found it less than forty, and often more 

 than sixty feet in thickness. Along the Republican I traced the 

 formation almost to the western line of the State, its thickness 

 ranging from thirty to seventy feet. One section north of Kearney, 

 on Wood River, showed a thickness of fifty feet. The same varia- 

 tion in thickness is found along the counties bordering on the Mis- 

 souri. One peculiarity of this deposit is that it is generally almost 

 perfectly homogeneous throughout, and of almost uniform color, 

 however thick the deposit, or far apart the specimens have been 

 taken. I have compared many specimens taken 300 miles apart, 

 and from the top and bottom of the deposits, and no difference could 

 be detected by the eye or by chemical analysis. 



Over So per cent of this deposit is very finely comminuted silica. 

 When washed in water, left standing, and the water poured off, and 

 the coarser materials have settled, the residuum, after evaporation 

 to dryness, is almost entirely composed of fine silicious powder. 

 So fine, indeed, are the particles of silica, that its true character can 

 alone be detected by analysis or under a microscope. About ten 

 per cent is composed of the carbonates and phosphates of lime. 

 These materials are so abundant in these deposits, that they spon- 

 taneously crystalize, or form concretions, from the size of a shot to 

 that of a walnut; and these are often hollow or contain some or- 

 ganic matter, or a fossil, around which the crystallization took 

 place. Almost anywhere, when the soil is turned over by the plow 

 or in excavations, these concretions may be found. Often, after a 

 rain has washed newly-thrown-up soil, the ground seems to be lit- 

 erally covered with them. Old gopher hills and weather beaten 

 hill-sides furnish these concretions in unlimited quantities for the 

 geologist and the curiosity hunter. When first exposed, most of 

 these concretions are soft enough to be rubbed fine between the 

 fingers, but they gradually harden by exposure to the atmosphere. 

 This deposit also contains small amounts of alkaline matter, iron, 

 and alumina. For the purpose of showing the homogeneous 

 character and the chemical properties of the Loess deposits, I have 

 made five new analyses of this soil. No. 1 is from Douglas County, 

 near Omaha; No. 2 from the bluffs near Kearney; No. 3 from the 



