316 GEOLOGY. 



These are often in combination with alkalies, and have already 

 "been discussed in the chapter on the Pliocene. Fine beds also exist 

 -on the Loup, Elkhorn, Logan, and Oak Creek. The great beds 

 of sand on the Platte contain some organic matter, and the sand 

 itself is contaminated more or less with iron, which is the character 

 of many other deposits in the State. The beds on the Elkhorn 

 above West Point are noteworthy for their purity. The drift in 

 -many places abounds in beds of pure sand, and the principal diffi- 

 culty in obtaining it comes from the thickness of the overlying 

 Loess. In the Pliocene Tertiary region where cuts, ravines or 

 bluffs exist, all grades from very fine to coarse can readily be ob- 

 tained. 



Lithographic Stone, of Upper Carboniferous age, exists near Syra- 

 cuse, in Otoe County. It is of medium quality. The extent of the 

 deposit has not yet been ascertained, but the indications are that it 

 may be sufficient to make it of mercantile importance. 



Iron Ores have not yet been found in beds thick enough to work. 

 The limenite of the Dakota Group, which is the best ore in the 

 State so far as known, occurs only in thin layers of a few inches in 

 thickness. 



Zinc and Lead are frequently found in small quantities, but no- 

 where yet has enough been obtained to justify extensive prospect- 

 ing. The geological indications are not favorable for their presence 

 in large quantities any where in the State. 



Gold in minute quantities is occasionally found in the sands of 

 the Platte, Nebraska, and other^ streams. But as our geological 

 formations are all more recent than those producing gold, we have 

 no scientific reason to suspect its existence within our borders. The 

 .minute quantities along our river beds no doubt came from the 

 mountains by drift agencies. 



Marl Beds are exceedingly abundant in some sections of West- 

 ern Nebraska. They are specially characteristic of the Tertiary 

 deposits, and vary a great deal in character and in appearance. 

 The dominant colors are greenish, yellowish, and whitish. They 

 .are beautifully exposed on the driftwood south of Culbertson, close 

 by the river bank. Here there are sections of marl exposed, from 

 four to eight feet in thickness, and of green and yellow color. The 

 green marls are specially rich in potash and iron, and their various 

 -compounds. Similar beds are found in many other places along 

 the Republican and its tributaries as far as to the western line of the 



