330 GEOLOGY OF THE BLACK HILLS. 



bonifcrous. The entire fauna of the Black Hills l^eds closely resemljle 

 that from Wisconsin ; although the species are nearly all distinct, the 

 "•eneric fasces is the same throuofhout. Amonj? the fossils from the hijjfher 

 parts of the formation there are quantities of Plante remains belonging to 

 the genus Paloiophjcus, which I am informed cover the surface of the rocks 

 over large areas where exposed, being densely matted together. These 

 beds also hold a position similar to the plant beds of other localities. 



The Jurassic formations seem also to be well represented in this region, 

 and many of the beds are highly fossiliferous. The species are not numer- 

 ous, but the individuals are extremely abundant, many of the slaty calca- 

 reous layers being so largely composed of organic remains, mostly Lamel- 

 libranchiates, as to be quite friable and easily broken in the hand, and some 

 of the sandy layers have their surfaces densely covered with the separated 

 shells of one or two species. The absence of Gasteropoda is a noticeable 

 feature at all localities from which specimens have been brought, no 

 example of this class of mollusks being present in the entire collection 

 from this formation. The few species of Fresh- water Gasteropoda described 

 as probably from this horizon in the Smithsonian contributions (Paleon- 

 tology of the Upper Missouri) being still doubtfully referred. This same 

 absence of Gasteropoda is also noticed in all the collections of Jurassic age 

 we have seen from the western countries, not more than three or four 

 species having been obtained beyond those above referred to. 



Among the Cretaceous fossils there are many forms of great interest, 

 especially among the Inocerami and Cephalopoda. Among the former the 

 forms described under the new generic name of Endocostea are interesting as 

 affording light on a group of shells which, although long known, have not 

 been fully understood, probably owing to the want of more and better 

 material which this collection has afforded, the feature there described hav- 

 ing previously been seen only on isolated poorly preserved specimens. 



Among the Ccplialopods of the Cretaceous there are some fine exam- 

 ples of the aberrant forms of the Ammonite Group, which show very conclu- 

 sively that a rich field awaits the future collector in this region. In some 

 of the localities of this formation from which collections have been brought 

 there a})pears to be a difficulty in recognizing the divisions of the group 



