230 DESCRIPTIVE GEOLOGY. 



Inoceramus, and by the rareness of coal seams. In the Laramie, on the 

 other hand, the marine fossils are mostly confined to the genus Ostrea. 

 The sandstones are less compact and more frequently impure, and stained 

 by oxide of iron, which also occurs in concretionary deposits of sufficient 

 extent at times to constitute an ore bed. They are characterized by a 

 greater development of clayey beds, and by the great number of coal seams, 

 of which as many as fifteen to twenty can frequently be observed in a seC' 

 tion of less than 1,000 feet, and by the presence of great quantities of leaves 

 and plant-remains, especially in the upper portion of the series. The thick- 

 ness given in the section for these two groups is about 3,000 feet for the 

 Fox Hill and 6,00) feet for the Laramie series. This thickness is deduced 

 from the angle and width of outcrop of the beds, and may therefore be 

 placed at rather a high figure, inasmuch as it is probable that there has been 

 some faulting, which would make this width greater than it should be nor- 

 mally. On the other hand, owing to the unconformity of the Tertiaries, 

 it is impossible to know how near the highest beds exposed may be to the 

 top of the Laramie series. 



In the region between Black Butte and Quaking Asp Mountain, and 

 also that to the west of the Leucite Hills, along the northern edge of the map, 

 there is a gap in our observations, and the outlines between the formations 

 in these regions are based on rather distant observations of the apparent line 

 of outcrop, a mode of geological study which gives a very fair approximation 

 to the truth in a country so bare of vegetation, and where the topographi- 

 cal features are so dependent upon geological structure, as this. On the 

 eiastern side of the anticlinal, the beds of the Laramie group were observed 

 principally in the region bordering the railroad from Black Butte Station 

 to the Salt Wells Valley. This region consists of low, broken ridges of 

 loose, friable standstone, having a general north and south trend, and east- 

 ern dip of from 5° to 7° within it are found local dips as high as 18°, which 

 point to a certain amount of dislocation in the beds. 



Owing to the generally low angle of inclination of the Laramie beds 

 on this side of the anticlinal, direct evidence of their non-conformity with 

 the overlying Tertiaries is difficult to obtain. Only two instances were 

 observed, one in the bluffs to the east of the railroad, a little north of 



