20 EXPLORING EXPEDITION FROM SANTA VK 



restricted to this geological horizon. In the upper part of this intermediate group of 

 Btrata, we have the BakeveUia, Pleurophorous, Axinvs, <('<■., of the beds above, anda Fauna 

 perhaps more Permian than Carboniferous, lmt below we soon reach a level where the 

 ( 'arboniferous types predominate. This group of strata lias been regarded by Professor 

 Swallow as all of" Permian age, while Mi-. .Meek terms it Permo-Carboniferous, draw- 

 ing the line which marks the base of the Permian at the base of the first group of mag- 

 nesian limestones, and restricting this term to those members of the series in which the 



Permian fauna predominates over the ('arboniferous. 



From this interlocking of the Carboniferous and Permian faunas, it is evident that 



the line of separation between the two formations must continue to be debatable 

 ground; and as there is, iii fact, a group which contains a mingled fauna — in truth, a 

 Permo-Carboniferous group — we must introduce this new member into the geological 

 series, or lix upon some conventional line which shall form the boundary between the 



summit of the Carboniferous and the base of the Permian formations. To avoid com- 

 plicating the geological scale, the latter course would undoubtedly be the wiser one ; 

 and since there is neither physical nor vital break in the series, it is perhaps not a 

 matter of great consequence whether the line be drawn at the horizon where the first 

 Permian type makes its appearance, or at the horizon beyond which the last Carbon- 

 iferous species ceases to exist, or even at the point, if indeed it were determinable, 

 where the species of the two formations are represented in equal numbers; in other 

 words, whether at the top, bottom, or middle of the Permo-Carboniferous group. It 

 will be secai by reference to the papers which have been before cited, that, while con- 

 taining several Permian types, the fauna of the "Lower Permian" group of Swallow 

 and Eawn has considerably more of the Carboniferous than Permian character; and 

 as greal bodies attract more strongly than small ones, it seems more natural that the 

 debatable ground should be ceded to the great and well-defined Carboniferous series, 

 of which the symmetry would suffer without it, rather than to the comparatively insig- 

 nificant and ill-defined Permian formation. It seems probable, therefore, that the 

 "Lower Permian" group of Swallow and Hawn will be regarded as an integral portion 

 of the Carboniferous system, while the term Permian will be restricted to the Permian 

 of Meek and Hayden, to the " Upper Permian" of Swallow and Hawn. It is evident 

 that only those strata should be regarded as Permian in which the Permian fauna pre- 

 dominates. 



In the hills bordering Dragoon Creek I first found limestones containing the group 

 of fossils — Pleurophorons, BakeveUia, Axinus, BeUerophon, &c. — towhichlhave referred 

 above. Farther west, toward Council Grove, the hills are capped with yellow mag- 

 nesian limestone, in many places crowded with the valves of BakeveUia parva. Over a 

 considerable area in this vicinity the highlands are occupied by what may be consid- 

 ered true Permian strata, while the valleys of all the water-courses are excavated to 



and into the Permo-Carboniferous, or, as I have called them, Upper Carboniferous 



strata. 



At Council Grove, Diamond Spring, Post Spring, and Cottonwood Creek, obser- 

 vations were made and fossils collected by Major Hawn, Messrs. Meek and Hayden, 

 and myself last year. The geology of all these points is nearly the same. At each the 



