ADomnrJ THE LOESS DEPOSITS. 245 



A brief description of a remarkable section through the Drift on Oak 

 Creek, Lancaster County, will not be out of place. A few miles from 

 Lincoln the terrace on this creek, composed of Loess materials, ap- 

 proaches the creek very closely. In this well the Loess deposit was fifteen 

 feet in thickness, then came two feet of Drift, then two feet of compact 

 peat, then clay and black soil, and then Drift again. The lower Drift 

 here probably represents the period of the first glacial advance. The 

 clay, black soil, and peat represent the middle period when the glaciers 

 had retreated and a new forest-bed covered the State. The Drift, imme- 

 diately on top of this, marks the second advance of the glaciers. The 

 Loess on top represents the final retreat of the glaciers, and that era of 

 depression of the surface of the State when the greater part of it con- 

 stituted a great fresh-water lake into which the Missouri, the Platte, and 

 the Republican Rivers poured their waters. 



THE LOESS DEPOSITS. 



The Loess deposits first received this name from Lyell, who observed it 

 closely along the Mississippi in various places. Hay den frequently calls it 

 the bluff formation, because of the peculiar configuration that it gives to 

 the uplands which border the flood-plains of the rivers. He also frequently 

 calls them marl-beds. This deposit, although not particularly rich in 

 organic remains, is in some respects one of the most remarkable in the 

 world. Its value for agricultural purposes is not exceeded anywhere. 

 It prevails over at least three-fourths of the surface of Nebraska. It 

 ranges in thickness from five to one hundred and fifty feet. Some sec- 

 tions of it in Dakota County measure over two hundred feet. At North. 

 Platte, 300 miles west of Omaha and on the south side of the river, 

 some of the sections that I measured ranged in thickness from one hun- 

 dred and twenty-five to one hundred and fifty feet. From Crete, on the 

 Burlington and Missouri River Railroad, west to Kearney, on the Union 

 Pacific Railroad, its thickness for 90 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 thick- 

 ness ranging from thirty to seventy feet. One section north of 

 Kearney, on Wood River, showed a thickness of 50 feet. The same 

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

 souri. One peculiarity of this deposit is that it is 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 80 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 dry- 

 ness, is almostentirely composed of fine siliceous powder. So fine, indeed, 

 are the particles of silica that its true character can alone be detected 

 by analysis or under a microscope. About 10 per cent, is composed of 

 the carbonates and phosphates of lime. These materials are so abundant 

 in these deposits that they spontaneously crystallize, or form concretions, 

 from the size of a shot to that of a, walnut; and these are often hollow 

 or contain some organic matter, as a fossil, around which the crystalliza- 



