THE STRATIGRAPHY AND INVERTEBRATE FAUNAS OF 



THE JURASSIC FORMATION IN THE FREEZE-OUT 



HILLS OF WYOMING. 



BY W. N. LOGAX. 

 With Plates XXV to XXXI, inclusive. 



INTRODUCTION. 



npHE present article is based on the study of an assemblage of fos- 

 -*- sils collected by members of the Kansas University paleontologic 

 party from the Freeze-out Hills of Wyoming during the summer of 

 1899. The expedition was under the direction of Dr. S. W. Willis- 

 ton, to whom the writer is indebted for assistance in securing these 

 data. 



The specimens described in this article will be placed in the Kan- 

 sas University Museum. The collections contain a majority of the 

 species which have been described from the interior Jurassic prov- 

 ince. A few of the species were collected by the writer from Como 

 Bluffs, and many of the species described from the Freeze-out Hills 

 were recognized there. 



Geographic Position. The Freeze-out Hills of Wyoming are situ- 

 ated in the region of the sixth standard parallel north, between lati- 

 tude 42^ and 42^ 15' north, and between longitude 106' and 106' 30' 

 west. Their most southern extension lies about fifteen miles north- 

 west of Medicine Bow, a station in southern Wyoming on the L^nion 

 Pacific railroad. Sixty or seventy miles east of them the lofty peaks of 

 the Laramie mountains rise, while the Seminole mountains approach 

 them from the west, and from them the Snowy range is jDlainly visi- 

 ble on the south. The extensive orogenic movements which produced 

 these surrounding mountain ranges left on the enclosed interior a 

 number of anticlinal folds, of which the Freeze-out is a type. The 

 hills, which are carved out of this anticline, are in the form of a semi- 

 circle, with a northwestern and southeastern extension of about 

 twenty-five miles. They are located about tw^enty miles north of the 

 region described by King in the report of the geology of the fortieth 

 parallel. 



Drainage. The Freeze-out Hills are separated from the Laramie 

 range by the basin carved out by the Little Medicine Bow river and 



[lC9]-K.U.Qr.-.A. ix 2-April, '00. 



