20 EXPLORING EXPEDITION FEOM SANTA FE 



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

 strata, we have the Bakevettia, Pleitrophorous, Axinus, c&c., of tlie beds above, and a fauna 

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

 Carboniferous types predominate. This group of strata has been regarded by Professor 

 Swallow as all of Permian age, while Mr. 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 Carboniferous. 



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

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

 ground; and as there is, in 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 fix 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 eqiial numbers; in other 

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

 will be seen 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 Hawn has considerably more of the Carboniferous than Permian character; and 

 as great 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 Pleurophorom, Bahevellia, Axinus, Jirl/ci-opkon, &c. to which I have referred 

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

 nesian limestone, in many places crowded with the valves of I><il;cr<>IH<( 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, Lost 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 



