REPORT ON THE PALEONTOLOGICAL FIELD-WORK FOR THE 



SEASON OF 1877. 



By C. A. White, M. D. 



The outfitting camp being- located on Owl Creek, twelve miles south 

 of Cheyenne, field examinations were begun in that neighborhood. This 

 district is one of considerable importance from the fact that the southern 

 boundary of the large region occupied by the deposits known as the 

 White River Tertiary Group, x>robably of Miocene age, passes through 

 it in an easterly and westerly direction. This formation is seen to rest 

 directly upon the lignite-bearing strata of the Laramie Group ; and al- 

 though the strata of both formations are so nearly level here as to betray 

 no unconformity^ deposition, the two are known to be unconformable by 

 sequence. In other words, certain Tertiary formations in the great Green 

 River Basin west of the Rocky Mountains, are now known to belong in the 

 geological series between the White River and Laramie Groups, although 

 they are seen in contact in the region under discussion. No special ex- 

 amination of the White River Tertiary beds was made upon this occasion, 

 except so far as to ascertain their general characteristics for immediate 

 comparison with the Laramie Croup, to which it was proposed to give 

 especial attention. The White River formation is known to extend from 

 Hie base of the mountains far out upon the great plains, and also far to 

 the northward; and wherever these beds exist in the broad reigon thus 

 indicated they cover those of the Laramie Croup, and are believed to 

 rest in all cases directly, although unconformably, upon them. In all 

 the great plateau region west of the Rocky Mountain Range proper,., the 

 extensively eroded and deeply carved strata of the Mesozoic and Ceno- 

 zoic formations are so perfectly denuded of the debris resulting from 

 their erosion that scarcely any impediment exists to their complete and 

 rapid study. Their investigation is still further facilitated by the spars- 

 ness of vegetation and the multitude of elevated points for observation 

 left as a result of deep erosion before referred to. In the plains east of 

 the mountains, however, even the same formations, retaining the same 

 lithological characteristics as those western ones just mentioned, while 

 they may have suffered much erosion in the aggregate, have been 

 eroded less deeply. Therefore the debris resulting from their erosion is 

 abundant upon the surface, and the free exposures of the undisturbed 

 strata are compatively few, except where they are irpturned. against the 

 immediate flank of the mountains. In that portion of the plains, how- 

 ever, which I examined in 1877, the 'exposures were sufficiently numer- 

 ous, aided by the extreme simplicity of the stratigraphic structure of the 

 region, to enable me to trace out the formations and to determine their 

 characteristics, without difficulty. 



The first exposures of the Laramie Group which I examined were 

 at and in the vicinity of some abandoned coal-mines about two miles 

 west of Maynard's Ranch, a few miles east of the foot-hills of the Rocky 

 Mountains, and about twenty-five miles south of Cheyenne. The strata 

 here are nearly level, or have only a slight dip to the eastward, and the 

 11 & s 101 



