THE TERTIARY PERIOD. 237 



The following is a section from the Loup, beginning at the top: 



1. Light brownish sand, of undetermined thickness. 



1. Loosely compacted saud and pebbles 21 feet. 



3. Greenish and gray marls 13 



4. Concretionary limestone 17 



5. Sand and sandy marls 16 



6. Concretionary limestone 11 



7. Soft lime and marl 7 



8. Silicious limestone, with concretions of limestone containing 



iron and alumina 16 



9. Fine loose sandstone, only eight feet exposed 8 



Total 109 



South of the Republican Valley, in Nebraska, on the Driftwood 

 there are some fine exposures of the Pliocene. The following sec- 

 tion, which I took in the spring of 1877, is from tow-nship 1 North 

 and 32 West, and on sections 12 and 14. It is numbered from the top: 



1. Loosely compacted sand and pebbles, with ebb and flow struc- 

 ture 10 feet, 



2. Alternations of greenish and gray marls 14 " 



3. Soft concretionary limestone 8 " 



4. Sandy marl 10 " 



5. Soft concretionary limestone 6 " 



6. Soft limestone and marl 4 " 



7. Silicious limestone, with pockets and concretions of pure 



white lime 14 " 



Total 55 " 



The strata in all these sections vary very much, even within a 

 quarter of a mile, and sometimes within a hundred yards. The 

 least variation is observed in the green marl beds. The section on 

 the Driftwood, it will be observed, is quite different from the ones 

 on the Loup and the Niobrara. On the south side of the Republi- 

 can, in Harlan County, the Pliocene rests on the Niobrara Cre- 

 taceous, and so far as I could observe, conformably, Here the ma- 

 terials consist largely of lime mingled with silicious materials. 

 Thick strata of marly silicious beds, and some beds of coarse, loosely 

 compacted sandstones, intercalated with them alternate below. I 

 regret that my section from this important locality has become 

 illegible, and I only describe it from memory. From Harlan County 

 to the west line of the State, along the Republican Valley, the 

 rocky bluffs of the valley are made up of a silicious limestone, 

 which often shades into a fine and then coarse conglomerate. The 



