CEETACEOUS NEAE TUE BLACK II ILLS. 31 



Ibis is probably tbe base of the Tertiary. Within a short distance to the 



west is: 



1. Dark gray Cretaceous clays (No. 4 of Meek and Hayden), with many nodnles 

 tilled with most beautifully preserved forms — Baculites ovatus, B. com- 

 2)>'cssus, Inoceraimis, Ammonites placenta, &c 40-50 



Cretaceous No. 5 was not recognized in the immediate vicinity. The 

 only observed evidence of unconformity between the two systems is the 

 nature of the coarse stratum (2). The Cretaceous in this vicinity is very 

 fossiliferous, yielding- to our hasty examination many beautiful and some 

 new forms, and it will undoubtedly afford an abundant harvest to a thorough 

 and systematic collector. From this point on the creek the Cretaceous 

 occupies the valley, but at several places there are evidences of a line or 

 lines of elevation similar to those already mentioned. Thus, at one place 

 on the northeast side of the creek a few miles below Old Woman Butte, 

 appears a cliff, 200 feet in height, of coarse yellowish and reddish sandstone, 

 having all the characteristics of the Dakota or lower Cretaceous sandstone. 

 Again, between this point and the Cheyenne several other lines of uplift 

 were passed, exposing a soft reddish sandstone, dipping 15° to 30° east. 

 Other points of upheaval in the vicinity of Old Woman Fork have been 

 noticed by Dr. Hayden, and in one place he records an exposure of the 

 entire series of the Cretaceous. 



The entire region seems to be crossed in a northwesterly direction by 

 upheavals which have involved the Cretaceous rocks. These ridges once 

 formed islands or reefs in the great Tertiary lake, which has deposited its 

 sediments around and over them, concealing now nearly all their irregu- 

 larities and only exposing them occasionally where the cloak of Tertiary 

 rocks has been removed by denudation. 



The valley of the Cheyenne, where it was crossed below the mouth of 

 Old Woman Fork, is cut to a depth of 250 to 300 feet in soft sandstone, 

 bearing a few thin seams of lignite. 



On the immediate north bank of the river the following- section was 

 exhibited in descending- order: 



o 



& 



13. Eed quartz conglomerate (feet) . . 5 



12. Soft yellowish sandstone (feet) . . 35-40 



11. Soft red sandstone (feet) . . 4 



