4 GIRTY 



lying beds has been found in so many points in the West that a 

 period of erosion previous to the earliest Pennsylvanian sedi- 

 ments can be hypothetized for all this Western country, a gen- 

 eralization which is all the more safe from the widespread evi- 

 dence of a similar occurrence in the central and eastern United 

 States, and indeed in other parts of the world. 



In some areas the Upper Carboniferous follows the Lower 

 without apparent unconformity and without marked lithologic 

 change, but still with a faunal break and the elision of Kas- 

 kaskia faunas. This is true of southern Arizona and perhaps 

 of the entire State, where the rocks of both epochs are lime- 

 stones formed, to all appearances, in an unbroken sequence ; 

 yet a faunal gap occurs, and even in this case, at least with the 

 present evidence, we must probably proceed on the h3'pothesis 

 that discontinuity, if not visible erosion, divided the 2 series of 

 sediments. 



The fauna of the Madison limestone, and that of the various 

 formations which must be correlated with it in different parts of 

 the West, has been said to be equivalent to those of the Kin- 

 derhook and Osage groups. This affinity is, however, especi- 

 ally with the Chouteau, and with the Cuyahoga fauna of the 

 Waverly group, which can probably be correlated wath it. 

 This fact is justly remarked by Mr. Weller,^ and was not un- 

 recognized by me, although it seems, I failed to call attention 

 to it. The Madison faunas lack many of the striking features 

 of those of the Burlington and Keokuk, both the wealth of 

 crinoids and such robust types as S^irifcr grimes?', S. logani, 

 Schizo^hoi'ia swallowi, Athyris incrassata, etc. In fact, while 

 the Lower Carboniferous rocks of the Mississippi Valley form 

 a standard section for the United States, it seems probable that 

 they are really the expression of somewhat abnormal conditions. 

 The aggregation of crinoid life, which is perhaps unequaled 

 the world over, if not the result of unusual conditions would at 

 least create them for the associated fauna, and to this fact may 

 perhaps be largely attributed the characteristic facies of the 

 Burlington and Keokuk groups. That these conditions were 

 widely spread seems to be certain, and they extended to or oc- 



' Acad. Sci. St. Louis, Trans., vol. ii, No. 9, 1901, p. 210. 



