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CHAPTEE I. 

 INTRODUCTION. 



The water-slied between the South Platte River and Lodge Pole Creek 

 is composed superficially of formations of the Pliocene epoch as defined 

 by Hayden. The latter stream flows eastwardly through the southern 

 parts of Wyoming and Nebraska, and empties into the South Platte 

 near Julesburgh, Nebr. The territorial and state boundaries traverse 

 this water-shed from west to east. The springs on its southern slope, 

 which form the sources of the northern tributaries of the South Platte, 

 issue from beneath the beds of the formation above named. At or near 

 this point is an abrupt descent in the level of the country, which generally 

 presents the character of a line of bluffs varying from two to nine hundred 

 feet in height. This line forms the eastern border of the valley of Crow 

 Creek until it bends to the eastward, when it extends in a nearly east and 

 ■west direction for at least sixty miles.* At various points along it, portions 

 have become isolated through the action of erosion, forming " buttes." 

 Two of these, at the head of Middle Pawnee Creek, are especially conspic- 

 uous landmarks, forming truncate cones of about 900 feet in elevation, 

 as Mr. Stevenson, of the survey, informs me. They are called the Paw- 

 nee or sometimes the White Bilttes ; near them stand two others, the 

 Castle and Court-House Buttes. 



The upper portion of this line of bluffs and buttes is composed of the 

 Pliocene sandstone in alternating strata of harder and softer consist- 

 ence. It is usually of medium hardness, and such beds, where exposed 

 on both the Lodg-e Pole and South Platte slopes of the watershed, 

 appear to be penetrated by innumerable tortuous, friable, siliceous rods 

 and stem-like bodies. They resemble the roots of the vegetation of a 

 swamp, and such they may have been, as the stratum is frequently filled 

 with remains of animals which have been buried while it was in a soft 

 state. No better-preserved remains of plants were seen. The depth of 

 the entire formation is not more than 75 feet, of which the softer beds 

 are the lower, and vary in depth from 1 foot to 20. The superior strata 

 are either sandstone conglomerate or a coarse sand, of varying thickness 

 and alternating relations ; the conglomerate contains white pebbles and 

 rolled Pliocene mammalian remains. 



This formation rests on a stratum of white, friable, argillaceous rock 

 of Miocene age, probably, of the White Eiver epoch, as I believe, from 

 the presence of the following species, which I detected in it: Mycvnodon 

 horridns, H. crucians^ Oreodon culhertsonii, 0. gracilis, Foehrothsriimi vil- 

 sonii, Aceraiherium occidentale, Hyracodon nebrascensis, Anchitheriiim 

 hairdii, Falcwlagus haydenii, Ischromys typus, Mus elegans, &c. The 

 formation extends to a depth of several hundred feet, and rests on a 

 stratum of a fine-grained, hard, argillaceous rock of a dark-brown color. 

 Some of its strata are carbonaceous, and contain vegetable remains 

 badly preserved; others are filled with immense numbers of fresh and 

 brackish water shells, including oysters. I do not know the depth of 

 this bed, but followed it to the southward until it disappeared beneath 

 the Loess of the South Platte. The age of this formation is identical 

 with that which underlies the fresh-water basins of Dakota and Wyo- 

 ming according to Hayden, and concerning which difference of opinion 



* SeeBerthoud, Procee<l. Acad. Nat. Sci. Phila., 1872, p. 48, where the bluffs are men- 

 tioned. 



