IK) HATCHER — OLIGOCENE AND MIOCENE DEPOSITS. [April 3, 



1. The Gering Sandstones. — These consist of some 200 feet of 



laminated, massive and cross-bedded sandstones, found either 

 conformably or unconformably overlying the White River 

 formation at various localities in western and northwestern 

 Nebraska. They are well shown at the mouth of Monroe 

 Creek canon, some five miles north of Harrison, Sioux 

 County, Nebraska. Few fossils have been found in these 

 sandstones. 



2. The Arikaree Sandstones. — These consist of some 500 feet or 



more of light- gray, soft, massive sandstones, everywhere 

 characterized by numerous, flattened, horizontally columnar, 

 hard, dark-gray concretions. These concretions have an 

 average vertical thickness of about one foot ; they are fre- 

 quently several yards in width and often several hundred feet 

 in length. They have a general northwesterly and south- 

 easterly trend. The Arikaree sandstones are especially well 

 developed in the northern face of Pine Ridge, in Sioux 

 County, Nebraska, and Converse County, Wyoming. In 

 this region these sandstones may be conveniently subdivided 

 into an upper and lower series, easily distinguishable both by 

 faunal and lithological characters. These subdivisions in 

 the Arikaree will be referred to and fully described later. 



3. The Ogalalla Fonnation. — This consists of a series of calcar- 



eous grits, loose brown sands and clays with occasional coarse 

 conglomerates, the whole attaining to an aggregate maximum 

 thickness of 300 feet. It is the equivalent of the Goodtiight 

 (Palo Duro) beds of Texas and Kansas, and is especially 

 well developed in western Nebraska and Kansas, between the 

 Platte and Arkansas Rivers. It is usually referred to the 

 Pliocene, but a portion, or all of it, may yet prove to belong 

 to the Miocene. 

 Returning to the Arikaree formation, I have already remarked 

 that in Sioux County, Nebraska, and Converse County, Wyoming, 

 it is lithologically and faunally divisible into two easily distinguish- 

 able horizons. Commencing below, these may be named and 

 characterized as follows : 



I. The Monroe Creek Beds. — These are well shown in the north- 

 ern face of Pine Ridge, at the mouth of the Monroe Creek 

 canon, five miles north of Harrison, Nebraska, where they 

 overlie the Gering sandstones, and are composed of some 



