CHAPTER VI. 



PALEONTOLOGICAL REPORT ON THE FOSSILS COLLECTED 

 BY THE UNITED STATES GEOLOGICAL AND GEOGRAPH- 

 ICAL SURVEY OF THE BLACK HILLS. 



By E. p. Whitfield. 



SECTIOlSr I. 



PEELIMINAEY EEMARKS. 



The species described in the following pages were collected in and 

 around the Black Hills during the expedition, and represent the different 

 formations recognized, except the Carboniferous; from which, the fossils 

 obtained were few and of little interest. 



The horizon of the Potsdam formation of the Black Hills appears to 

 be, so far as the fossils will serve to determine, about the same as that of 

 Wisconsin and the neighboring States, and of some of the layers the litho- 

 logical features are so nearly the same, that it would be difficult to distin- 

 guish between specimens from the two localities. The purplish-green 

 quartzitic rock from the head of Red Canon Creek, containing Lingulepis 

 pinniformis Owen, sp., and several other Brachiopodous shells, appears to 

 hold nearly the same relation to the rest of the group as does that at the 

 Falls of the Saint Croix, from which the species was originally described, 

 namely, near the base, the Red Canon Creek beds resting immediately on 

 the slates of older date (probably Huronian), while the Trilobitic beds and 

 the soft friable layers occur at a horizon of about 100 feet below the Car- 



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