THE RELATIONS OF SOIME CARBONIFEROUS FAUNAS I3 



suspected discordance separates the Genevieve from the Osage 

 groups, while the general unconformity preceding the Potts- 

 ville, which should intervene below the Morrow formation, is 

 relatively insignificant. The survey of the situation thus hastily 

 made, while inadequate to prove that the black-shale interval 

 constitutes the early portion of the Pottsville series, does seem 

 sufficiently to call in question the accepted disposition of these 

 beds, to entitle their correlation to appear among the interesting 

 Carboniferous problems of the United States. 



•There is also a chance that these beds may at the same time 

 represent both upper Mississippian and " Lower Pottsville," for 

 it can not as yet be demonstrated that part of the Pottsville is not 

 a nonmarine equivalent to the marine Genevieve, or a portion 

 of it; but from such facts as are known to me there seems little 

 likelihood for this to be the case. 



If the interval under consideration does not represent the 

 earlier portion of the Pottsville series, but corresponds to the 

 later epochs of the Mississippian series, it is evident that terra- 

 queous conditions, expressed in sediments and faunas, were very 

 different in the northern and southern parts of the inland sea. 

 This period would then present a case somewhat analogous to 

 that of the middle portion of the Devonian, which is represented 

 by varied sediments and faunas in New York, but to the south 

 and west, according to some views, is replaced by a single 

 uniform bed of nearly barren black shale. The peculiar de- 

 velopment of the Arkansas faunas from the Boone to the 

 Morrow might be explained as modifications imposed upon the 

 typical Genevieve fauna by the proximity to and occasional 

 invasions of black-shale conditions. Upon this hypothesis, also, 

 an exception to the statement that Genevieve faunas are almost 

 entirely lacking in the west, would be furnished in the case of 

 the White Pine shale of Nevada, w^hich is here provisionally 

 and in a general way aligned wath the interval above the Boone 

 in Arkansas. 



It is a matter of common knowledge that the Upper Carbonif- 

 erous faunas of the Western States differ to some extent from 

 those of the Mississippi Valley and the Appalachian region. 

 Part of this diversity, as already remarked, seems to be due to 



