12 GIRTY 



Pine shale — which he assigned to the " Upper Devonian." I 

 have long been of opinion, however, that the age of this bed is 

 not Devonian, but Carboniferous. The White Pine fauna, 

 however, is not without forms suggestive of the Devonian, to 

 which period it was also tentatively assigned by Meek. One 

 of the most striking of these is a Leiorhynchus resembling 

 L. quadricostaium. Prodtictiis hirsutiformis and a Posid- 

 onomya [Posidontella P) also lend it a Devonian aspect. A 

 Leiorhynchus like L. qjiadricostattwi, a Productus like P. hir- 

 sutiformis, similar Goniatites, and similar Posidoniellas are 

 found near the base of the Caney shale in Indian Territory, 

 and in the Spring Creek limestone and Fayetteville shale of 

 Arkansas. These facts, together with a similarity in lithologic 

 character and an identity in stratigraphic position, in point of 

 which each occurrence is immediately beneath beds supposed 

 to represent about the same horizon, while not sufficient to 

 demonstrate stratigraphic equivalence, for which a thorough 

 comparison of the entire faunas would be necessary, lend a 

 strong color of probability to it. The occurrence of the White 

 Pine shale corresponds to the Caney shale in that no beds of 

 Mississippian age underlie it. In Nevada, however, we have 

 a great thickness of Devonian, perhaps the most notable in- 

 stance of Devonian west of the Mississippi Valley, an equiva- 

 lent of which is lacking in Indian Territory. 



Assuming the correctness of the correlation thus tentatively 

 adopted, the uniformity of distribution of the black-shale hori- 

 zon with the overl3nng sandstone and limestone is suggestive of 

 a close relation between them. On the other hand, at the base 

 of this horizon a great discordance appears to exist, measured 

 to some extent by the various ages of the beds upon which it 

 rests, now Mississippian, now Ordovician, and again upon De- 

 vonian strata. On the hypothesis that this black-shale interval 

 represents the early portion of the Pottsville series, this appar- 

 ent unconformity at its base would probably coincide with the 

 period of erosion, almost continental in extent, by which the 

 Mississippian period was brought to a close. On the other 

 hand, on the assumption that the black shale belongs in the 

 upper Mississippian, it would appear that an extensive and little 



