36 GEOLOGY OF THE BLACK HILLS. 



presence of a very persistent stratum of quartz conglomerate several feet in 

 thickness, occupying the base of the Tertiary, we have a strong evidence of 

 a change of circumstance in the deposition of the sediments. 



These detached areas of Tertiary approach the immediate western 

 banks of the Cheyenne near French Creek, and on the opposite side of the 

 river portions of the White River deposits approach equally near, being 

 separated only by the deeply excavated valley of the river. There can be 

 no doubt that the two areas were once continuous, and are now separated 

 only as a result of erosion. The valley of the Cheyenne in the region of 

 Rapid Creek has a breadth of from one to two miles, and is cut from 150 to 

 200 feet in the shales and clays of the upper Cretaceous, which in this 

 vicinity and in the numerous creeks that here join it — Bull Creek, Bear 

 Creek, Sage Creek, etc. — contain abundant and beautifully preserved fossils, 

 especially of group No. 4. From this region our collections were enriched 

 with some of the most beautiful forms obtained on the expedition. The 

 river itself is shallow and narrow; the water contains much saline matter, 

 and is milky with fine suspended clay. 



Near Rapid Creek the summit of the eastern bank of the Che} T enne 

 extends eastward in a broad plateau for six or seven miles, when the edge is 

 suddenly reached, and spread out below in a seeming basin lie the wondrous 

 bad lands of the White River Tertiary. They are carved into the most 

 fantastic shapes ; castles and pinnacles, domes and minarets, cover the 

 surface, all hewn -in drab and flesh colored clays, and it seems almost as 

 if they were a ruined city of the dead, rich in the fantasies of a forgotten 

 architecture. The valleys of the several streams that rise in this bad-land 

 country and flow into the Cheyenne — Sage Creek, Bull Creek, etc. — have a 

 peculiar funnel-like shape, with their broader parts in the Tertiary and their 

 narrow portions cut through the Cretaceous to the river. 



From the mouth of the Rapid the surveying party ascended the 

 Cheyenne River to near the mouth of Burntwood Creek, and then, cross- 

 ing eastward to the White River, joined the main body of the military 

 escort, which had crossed through the Bad Lands from near Spring Creek. 

 Thence following up the White River, via the Indian agencies of Spotted 



