Article XII.— ON JURASSIC STRATIGRAPHY IN 

 SOUTHEASTERN WYOMING. 



By F. B. LooMis. 

 Plates XXVI and XXVII. 



The purpose of this paper is to give some details in regard to 

 the Jurassic strata of Wyoming, in which, for the last four years, 

 the American Museum of Natural History has collected Dinosaur 

 remains. Very little detail geological work has been done in the 

 region. Prof. W. C. Knight published a map of southeastern 

 Wyoming showing the Jurassic exposures'; and this is in part 

 reproduced, with his consent, in Plate XXVI, Fig. i, to show the 

 location of the area in which the succeeding maps and sections are 

 located. Prof. W. N. Logan " has also published a section- made 

 in the Freezeout Hills. The area studied, lying along the 

 county line between Albany and Carbon Counties, includes all 

 of the quarries worked for the American Museum; and, inciden- 

 tally, a considerable number of Marsh's localities, where they 

 were within the area mapped, are indicated. 



Referring to Plate XXVI, Fig. i, the axis of the Laramie 

 Mountains is seen in the eastern part of Albany County, extend- 

 ing nearly north and south; but in Converse County it bends 

 until it extends nearly west. In the angle thus formed are 

 situated four short (8-20 miles in length), sharp folds, known 

 as the Medicine, Como, Prager, and Miser anticlines. Their 

 axes lie northeast and southwest, and each fold is thrust over be- 

 yond the vertical on its northern side. These folds are radial 

 folds formed at the edge of the territory affected when the 

 Freezeout Hills were thrown up. AVhile the Laramie Mountains 

 seem to be due to a thrust from the east, there must have been a 

 force acting from the north in the neighborhood of the Freezeout 

 Hills. This thrust from the north seems to have affected locally 

 the axis of the Laramie Mountains, bending it to an east and 

 west direction. The four short anticlines above named die out 

 on the eastern boundary of the territory affected by the thrust 

 from the north. How far west this thrust from the north, to 

 which the Freezeout Hills are due, acted I cannot say. 



It is along the southern exposures of Medicine and Como anti- 



' Bull. Geol. Soc. America, Vol. XI, p. 377, igoo. 

 ' Kan. Univ. Quart., Vol. IX, p. log, iqoo. 



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