1902.] DOUGLASS — CRETACEOUS AND LOWER TERTIARY. 215 



is said that this layer extends for twenty miles up Fish Creek, 

 but I have not tried to trace it, so do not know whether it is con- 

 tinuous or not. It is also said that these fossils gave the Mussel- 

 shell River its name. Here we may be quite sure that we are in the 

 Laramie, for fresh or brackish water conditions prevail, but it prob- 

 ably extends between looo and 2000 feet below. 



Still higher are shales forming a flat or depression, above which 

 are conical hills or hog-backs — the remains of dissected ridges cut 

 through by ravines and by streams which are fed by springs in the 

 Fort Union sandstone above. These hills or ridges are capped with 

 brownish, compact, laminated sandstone. No fossils were seen 

 except fragments of wood in the shale. 



Above these sandstones dark shales again predominate. I cannot 

 tell, at least without more careful study and observation, where the 

 Laramie terminates and the Fort Union begins. In fact, it looks 

 as if there were in this section almost continuous deposition from 

 the Jurassic up. We found here no traces of the volcanic material 

 of the Livingston formation, which only thirty or forty miles to the 

 southwest is so well developed. It appears that here deposition 

 went on quietly and uninterruptedly. There is little doubt that 

 part of the strata were deposited synchronously with those of the 

 Livingston. Here, so far as we have discovered, as in other places. 

 Nature has left no way marks and laid down no boundary line to 

 distinguish between the great ''Age of Reptiles " and the ''Age of 

 Mammals." There appears to be no sign of the disturbance that 

 is supposed to have closed the Mesozoic and brought in a new order 

 of things; yet only a few miles away there was a region of upheaval 

 and of intense volcanic activity. The strata in the section under 

 consideration have been disturbed, but the Tertiary beds are also 

 involved in the upheaval. Perhaps microscopic or chemical exam- 

 ination may reveal the presence of fine volcanic material here. 



Mr. W. Lindgren made three different measurements of the Lara- 

 mie to the eastward of this region (see Tejiih Census of the United 

 States, Vol. XV, p. 744). In none of these does he make the 

 thickness of the Lower Laramie to be less than 7000 feet. I do not 

 think that this, as C. A. White ^ thinks probable, includes the Belly 

 River, or anything lower than Fort Pierre. Lindgren's Upper 

 Laramie, or Bull Mountain series, is probably Tertiary — apparently 



1 « Correlation Paper, Cretaceous," Bull. S4, U. S. Geol. Survey, p. 174. 



