PALEONTOLOGY OF THE BOULDER AREA 99 



and the cephalopods heretofore mentioned, seem to be confined to a 

 very narrow band of limestone, which is continuous through each out- 

 crop, but whether continuous between outcrops is not known. Other 

 similar bands exist at each outcrop, but are not fossiliferous. 



Fish. — A few fish scales have been found in the lower part of the 

 formation, in a hard, very black limestone, near an igneous intrusion 

 south of Left Hand Creek. 



Fossil sea weeds and a few fossil mollusk or worm borings are found 

 in the sandy zone near the top of the formation. 



NIOBRARA 



Inoceramus dejormis. — This large species is found in abundance at 

 every Niobrara outcrop, being confined chiefly to the upper strata of 

 the basal limestone and the lower part of the superincumbent shales, 

 and often covered with Ostrea congesta. 



Inoceramus simpsoni. — A fragment from the fold five ' miles north 

 of Boulder seems to be of this species, but there is not enough of it to 

 make identification certain. 



Inoceramus sp. — Fragments of a large undetermined species were 

 found at the lime kiln in the western edge of Boulder, and five miles 

 north of Boulder. 



Ostrea congesta. — This small oyster is found in the basal limestone 

 attached to /. dejormis, and abounds at a higher horizon in the shales, 

 where, with large, flattened, undetermined Inoceramus, it forms thin 

 bands — continuous for long distances. This horizon and the /. dejormis 

 horizon may be recognized at almost every outcrop of the formation. 



Fish. — Mr. F. A. Fair has brought in one fish tooth from this form- 

 ation at Coal Creek, south of Boulder, and Mr. H. F. Watts found 

 fish scales in Upper Niobrara north of Boulder. 



FORT PIERRE 



This formation consists of about seven or eight thousand feet of 

 shales with a strong easterly dip, differing very little in lithological 

 characters with the exception of a persistent sandstone in the lower 

 half. In the absence of recognizable lithological horizons, the discovery 

 of definite paleontological horizons which may be depended upon would 



