4 UNIVERSITY OF MISSOURI STUDIES [152 



Boulder Canon the red sandstone walls are vertical. These 

 perpendicular sandstone crags are the most striking feature 

 of the scenery of the foot-hills. 



Lying next to the Fountain sandstone, and also of Pennsyl- 

 vanian age, is the creamy Lyons sandstone, which is quarried 

 in large amounts. It has a maximum thickness of almost 300 

 feet. 



Next in order, and still of Pennsylvanian age, is the Lykins 

 formation, about 800 feet thick and consisting of sandstones, 

 sandy shales, and a little limestone. It is easily weathered and 

 is consequently thickly covered with waste. 



The Morrison formation occurs next, and consists of sand- 

 stone, clays, and limestone, and is a little less than 600 feet 

 thick. It is of Jurassic age. 



Then come various Cretaceous beds, the first of which, 

 the "Dakota," is a firm sandstone of about 350 feet in thickness. 

 Its resistance to weathering causes the characteristic hogback 

 of the foot-hills, consisting of one, two, or even three distinct 

 combs, or crags. . 



Then follow in succession the Benton shales, 500 feet 

 thick ; the Niobrara shales and limestones, 400 feet thick ; the 

 Pierre shales, 5,000 feet thick; the Fox Hills shales, 1,300 feet 

 thick; and the Laramie beds, which are coal-bearing and about 

 115 feet thick. Lastly are the Quaternary deposits of allu- 

 vium and terrace gravels. The various shales have weathered 

 and eroded rapidly and underlie the plain, while the more 

 resistant beds next the granite persist as crags, while the high 

 mesas at the base of the foot-hills are shale outliers left by 

 stream-erosion and are really stream terraces. 



The soil of the region, outside of the alluvium and ter- 

 race gravels, is granitic in the mountains, while in the foot- 

 hills it is apt to be brick-red from the detritus of the red 



