LOGAN : FREEZE-OUT HILLS OF WYOMING. 115 



22. Brown to bluish -gray arenaceous limestone 8 in. to 1 ft. 



This stratum contains the following non-marine invertebrate forms : 



Unio knighti, U. loillistoni, U. haileyi, Valvata leei, and (Planorhls) 

 vetei'nus. Species from the same genera have been described by 

 Meek from a similar stratum of limestone in the Black Hills. As 

 these occupy much the same stratigraphical position they are proba- 

 bly the same age. The Lloplacodes seems to be identical with that de- 

 scribed by Meek in the Geology of the Upper Missouri. 



23. Drab-colored clay 70 ft. 



Species of the genera Brontosaurus, Blplodociis, Morosaurus, 



Stegasaurus and AUosaurus occur in this horizon. Portions of spe- 

 cies of all these genera were found in one quarry by the Kansas Uni- 

 versity collecting party. The clay is of that quality usually designated 

 as "joint" clay. It contains in places iron and argillaceous concre- 

 tions of small size. The iron, and sometimes the bones, are covered 

 with selenite crystals. 



21. Grayish-white sandstone .^)0 ft. 



This layer forms a conspicuous capping for the hills, and is the 

 highest remnant of the anticline. It breaks up into large blocks, 

 which lie scattered along the slopes of the underlying softer beds. 

 Its erosion and disintegration is accomplished chiefly by sapping. 

 No fossils were found in this .stratum, and its true position is in 

 doubt. 



The Dakota. The Freeze-out Hills are capiDed with a heavy ledge 

 of sandstone, which may represent the basal member of the Dakota, 

 although its age is in doubt. So far no paleontologic evidence as to 

 the age of these beds has been found. From their stratigrapliical 

 position, however, they have been placed in the Dakota. 



This grayish-white sandstone layer breaks up into immense blocks, 

 which lie scattered in many places from summit to base of the hills. 

 j It weathers in some places to a rusty iron color, and in other places has 

 I the appearance of hematite. The base of the sandstone is apparently 

 1 conformable with the underlying beds, although it is conglomeratic. 

 The stratum forms the crests of the greater part of the hills and dips 

 rapidly down toward the surrounding plain. Its detailed stratig- 

 raphy, taken from an outcrop about one mile northwest of the T. B. 

 Huch, is as follows: 



1. At the base, resting on the clay of the Atlantasaurus beds, a 

 I layer of fine-grained sandstone G ft. 



2. A layer of conglomerate, composed of small pebbles 10 " 



3. A layer of coarse-grained sandstone 10 " 



4. At the summit, fine-grained sandstone 25 " 4- 



9-K.U.Qr. A-ix2 



