212 KNOWLTON 



Platanus nohilis Newb. 

 Legumino sites arachioides Lesq. 

 Sapindus sp. 

 Viburnum whymperi Heer. 



17. BIGHORN BASIN, WYOMING. 



The following discussion of the lower Fort Union in this area is 

 based on the published work of Mr. C. A. Fisher's,^" personal obser- 

 vations made during the seasons of 1907 and 1908, and the work of 

 United States Geological Survey field parties under the charge of 

 Mr. E. S. Woodruff, made during the same years. In the extreme 

 northwestern part of the Basin the lower Fort Union undoubtedly 

 connects with the area about Red Lodge, Montana. At the time 

 Mr. Fisher's paper was prepared sufficient paleontologic data had 

 not been obtained to fix definitely the limits of this, as well as under- 

 lying and overlying beds, and the whole series, aggregating more 

 than 5000 feet in thickness, was described and mapped as ' Laramie 

 and associated formations.' As shown on Fisher's map, these beds 

 are exposed continuously about the outer edge of the Basin, having 

 their maximum areal extent in the northeastern portion and their 

 minimum exposure along the northwestern border just below the 

 Montana state line. 



The lowest member of the aggregated ' Laramie and related forma- 

 tions,' resting upon the Pierre, is composed of about 300 feet of a 

 "massive gray to buff sandstone," which lithologically resembles the 

 supposed 'Fox Hills' on the eastern side of the Bighorn Mountains, 

 and for this reason was tentatively referred to the 'Fox Hills. ' The 

 few invertebrates do not serve to fix definitely the age, according to 

 Stanton,'* since they may occur below the Judith River as well as in 

 Fox Hills. Above these beds, whether with or without an erosional 

 interval is not definitely known, comes the great thickness of Fort 

 Union which Fisher has shown may be divided into two parts. The 

 lower member, which corresponds to the beds already so extensively 

 traced, is composed of dark sandstones, shales and clays with occa- 

 sional seams of coal and coaly shales. Throughout the lower por- 



*" Geol. and Min. Res. Bighorn Basin, Wyoming: U. S. Geol. Surv., Prof. 

 Paper 53, 1906, p. 31 et seq. 



*' In Fisher, Bull. U. S. Geol. Surv., Prof. Paper, 53, p. 32. 



