VALLEY OF THE NORTH PLATTE. 155 



the old overland stage-road crosses the river, was taken from the water- 

 level to the top of the overlying bench : 



1. Hard rusty-gray sandstone x 



2. Black shales, with thin sandstone layers, carrying Ostrea 50 feet. I 



3. Friable yellow sandstone, rich in the genus Ostrea 30 feet. ^450 feet. 



4. Eeddish-yellow sandstone I 



5. Grayish- white sandstone / 



Of all the sandstone strata exposed in this region, those from Saint 

 Mary's Peak appear the most compact, forming a hard, distinctly-bedded 

 rock, of a steel-gray color, and carrying but little iron. An analysis of the 

 Saint Mary's Peak sandstone was made by Mr. B. E. Brewster, with the fol- 

 lowing result : 



Silica 94.76 



Alumina 2.99 



Ferric oxide ■ 0.23 



Lime - 0.21 



Soda - ,. . . 0.13 



Potassa 0.41 



Ignition 1.10 



99.83 



