EASTERN FOOT-HILLS. 55 



eating dips of 6° to 8°. Near Park's Station were found the following 

 Colorado Cretaceous forms : 



Inoceramus prohlematicus. 

 Inoceramus difformis. 

 Inoceramus Barrahini. 



The lower geological section, which is given at the bottom of Map I, 

 and crosses the Colorado Range and the Cretaceous plain, cuts tlie ridges 

 nearly at right angles between 3 and 4 miles south of Park's Station. Here 

 the Red Beds form a well-marked sandstone ridge, with a dip of 20°. The 

 Jurassic marls, with the included limestones, occupy a slight depression at 

 the base of the more elevated Dakota Cretaceous, which here consists of a 

 hard, compact sandstone, inclined also at 20° toward the plain, but present- 

 ing an abrupt wall on the western side. The Colorado group occupies a 

 valley along the base of the Dakota wall, with the lower formation clearly 

 represented. 



From the Cache la Poudre to the Big Thompson, a distance of 15 

 miles, the ridges present considerable uniformity, both in structural and 

 lithological characters. The general strike is a few degrees west of 

 north, with an average dip from 18° to 22° ; both the Red Beds and Da- 

 kota sandstone maintaining the same average dip. Proceeding southward, 

 the Red Beds would appear to increase gradually in thickness, and to dis- 

 play more variety in color toward the top, with a loose friable texture. 

 The valley, or depression, which has been already mentioned as frequently 

 lying between the Triassic and Dakota sandstone, and occupied by the 

 Jurassic marls, here becomes a marked topographical feature, arising in 

 part, no doubt, from the sandy, easily-eroded summits of the Red Beds, 

 and in part from the nature of the rigid quartzite wall of Dakota sand- 

 stone. The Dakota beds here attain a development of nearly 300 feet, 

 which is their maximum thickness east of the mountains. At the base of 

 tlie Dakota the conglomerates, which form so persistent a feature, are 

 exposed in a hard compact quartzite rock, which is overlaid by sandy 

 saccharoidal beds, in turn overlaid by a second quartzite. All the divisions 

 of the Colorado group crop out to the eastward, but with the same litho- 



