BOWLDER DEPOSITS. 25 



The thickness of the conglomerate varies from 25 feet to nothing. In 

 places it graduates from the maximum thickness to a feather edge; elsewhere 

 it merges imperceptibly into the underlying rocks. In the weathering of 

 the borders of the Chiigwater there are often found buttes or pinnacles, 

 detached from the face of the cliff and capped by conglomerate. The con- 

 glomerate contains large quantities of the chalcedonic quartz, which is so 

 constant an associate of the Tertiary in the West. The agate formations 

 are often of great beauty and commonly contain the black dendritic dis- 

 seminations to which the name "moss" has been applied. In certain places 

 on the Chugwater the accumulations are large, and many hundreds of 

 pounds have been collected for ornamental purposes. 



On the surface of the Plains along the road south of the Chugwater there 

 is found a very extensive accumulation of gravel, pebbles, and small bowl- 

 ders, that have been carried down from the mountains at the west and from 

 the beds outcropping at their base. On Horse Creek this formation attains 

 a thickness of 10 to 20 feet and is composed largely of granitic fragments, 

 while from Lodge Pole to Bear Creek it is peculiar in containing a large 

 quantity of labradorite fragments. Frequently it is cemented by a calcare- 

 ous cement. Wherever found, the deposit is largely made up of pieces of 

 the older sedimentary rocks which underlie the Tertiary and outcrop along 

 the base of the mountains at the west. Fragments of Carboniferous lime- 

 stone with its characteristic fossils are numerous. No bowlders nor frag- 

 ments were noticed with a greater diameter than two feet, and few are more 

 than six inches in diameter. 



So far as our rapid and superficial examination extended, this bowlder 

 deposit is more strongly developed at or near the margins of the valleys 

 draining from the Laramie Mountains, as though it was the result of the 

 denuding and carrying power of streams once larger and filling those 

 channels, rather than of a more wide-spread and general agent of denunda- 

 tion and distribution. 



Where the road crosses the divide between the valley of the Chug- 

 water and that of the Laramie, there are cliffs showing from 100 to 200 

 feet of the soft, light-colored beds of the White River Tertiary, overlying 

 the conglomerate of the Chugwater Valley. 



