120 PROCEEDINGS OF THE WASHINGTON MEETING 



LITHOGENESIS AND STRATIGRAPHY OF THE RED BEDS OF SOUTHEASTERN 



WYOMING 



BY S. H. KNIGHT J 



(Abstract) 



The principal object of this paper is to announce the results thus far ob- 

 tained from a detailed study of the red beds of southern Wyoming. This 

 study is an attempt to determine, first, the origin and source of the sediments 

 of which the red beds are composed ; second, the physical conditions which 

 were active during their deposition ; and, lastly, their relations to contem- 

 poraneous and adjacent formations. The sections thus far studied in detail 

 are exposed along the eastern flank of the Medicine Bow Mountains and along 

 the western flank of the Laramie Mountains. This region affords a good 

 opportunity for a study of this nature, inasmuch as there is a striking change 

 in the lithological character of the lower half of red-bed series, as first brought 

 out by my father, W. C. Knight, and later emphasized by Darton. 



The change in lithological character throws considerable light on the direc- 

 tion from which the material was derived and the distance which it has been 

 transported. Along the eastern flank of the Medicine Bow Range the lower 

 half of the red-bed series (Casper formation) consists of about equal amounts 

 of conglomeratic arkose and sandstones, with a very minor development of 

 shale, while the same formation 20 miles to the east, along the western flank 

 of the Laramie Range, exhibits in one section, which may be taken as typical, 

 the following: arkose, 2 per cent; sandstone, 61 per cent; shale, 22 per cent, 

 and limestone, 15 per cent. The total thicknesses of the formations in the 

 two localities are 710 feet and 6S7 feet respectively. Owing to the size, angu- 

 larity, and freshness of the feldspars in the conglomeratic arkoses, one may 

 say that the material has not been derived from any great distance ; this, to- 

 gether with the fact that these arkoses are practically wanting in the Laramie 

 Range section, leads one to believe that the material had its origin to the 

 west, probably from the region now occupied, in part at least, by the Medicine 

 Bow Mountains. The evidence for the upper half of the series is not so clear, 

 but it is hoped that some petrographical and mechanical analyses now being 

 conducted will throw some new light on the problem. 



We may now turn to the physical conditions which influenced the deposition 

 of the red beds in this region. The evidence points to a continental origin for 

 a large part of the series. Torrential, fluvatile, and eolian deposits have been 

 recognized. The evidence for a continental interpretation may be summed up 

 as follows: (1) Lack of continuity in sections measured at short intervals: 

 (2) channeling to a depth of 10 or more feet; in one section seven erosion 

 intervals were noted within 450 feet of the base of the section; (3) the ever- 

 prevailing cross-bedding of both the torrential and eolian type: (4) the char- 

 acter of the material; (5) color; (6) lack of marine fossils. In this con- 

 nection I wish to call attention to a striking conglomerate 150 feet from the 

 base of the series, in an exposure on Sand Creek, Albany County, Wyoming. 

 This conglomerate has a thickness of 34 feet and consists for the most part of 

 water-worn pebbles and boulders of an igneous rock nature, the maximum 



1 Introduced by A. W. Graban. 



