THE RELATION OF SOME CARBONIFEROUS FAUNAS 3 



English *' Mountain limestone." This species is not known 

 elsewhere in North America, unless a form identified by Meek 

 as Productus latissiiuus prove to be the same. The latter was 

 found on Katlahwoke Creek, Montana, and is the only indica- 

 tion of the Baird fauna known to me east of the Pacific coast.' 

 If it does mark this fauna, the latter will appear to have had a 

 wider distribution eastward than there is otherwise ground for 

 supposing. There is thus no very conclusive evidence for be- 

 lieving that the Bairdian fauna was contemporaneous with those 

 of the Mississippi Valley, rather than of later development, but 

 even if so the facies of the two are so different that the pro- 

 priety of extending to the California fauna the term Mississip- 

 pian may well be questioned. 



The fauna of the Madison limestone, which has so wide a 

 distribution in the West, is, on the other hand, closely related 

 to the typical Mississippian faunas. In my earlier work I cor- 

 related the Madison limestone with the Kinderhook, Burling- 

 ton, and Keokuk groups of the Mississippi Valley, and have 

 seen no reason since to change my views. Nevertheless, it 

 seems to be almost unquestionable that in some areas these 

 Western faunas, in their later developments, take on the aspect 

 characteristic of the St. Louis epoch. Nowhere in the West, 

 however, have any Kaskaskia faunas been discovered. One of 

 3 hypotheses seems necessary to explain this fact, which is no 

 less striking, even should local areas of Kaskaskia rocks sub- 

 sequently be discovered. Either no strata equivalent to the 

 Kaskaskia have ever been deposited in this region ; or, though 

 deposited, they have since been removed ; or else contempora- 

 neously formed sediments supported a fauna which was so 

 unlike the Kaskaskia that its equivalence has failed of recog- 

 nition. Of these 3 hypotheses it is probable that the second is 

 the correct one. Unmistakable evidence of unconformity be- 

 ween the Madison limestone (and its correlates) and the over- 



' I have recently identified P. giganteus in Alaska, though somewhat doubt- 

 fully, and a small form apparently related, though more distantly, occurs in 

 Utah at a horizon above the Madison (Waverly) fauna. The latter occurrence 

 affords some slight ground for the hypothesis that the Bairdian fauna, while 

 quite different, may possibly be equivalent to the upper Mississippian faunas 

 which otherwise are not represented in the West. 



