GEOLOGICAL SURVEY OF THE TERRITORIES. 289 



mon in our western coal measures, and scarcely any of the coal-uieasure 

 Gasteropoda, and none of the Polyzoa, Foraminifera, corals or fish re- 

 mains, when viewed in connection with the affinities of the forms men- 

 tioned, certainly imparts quite a Permian aspect to this little group of 

 fossils. 



On the other hand, when we bear in mind the fact above stated, that 

 all of the species, so far as they can be identified, are certainly known 

 to range far down into the unquestionable coal-measures of the western 

 States, while we here also find associated with them a Phillipsia, a 

 genus entirely unknown in the Permian of Europe, and even belonging 

 to an order or sub-order of Crustacea, not certainly known to have ex- 

 isted after the close of the Carboniferous epoch, we at once see the ne- 

 cessity for caution in referring this rock to the Permian, on such evi- 

 dence. 



Every one familiar with the organic remains of the coal-measures of 

 the Mississippi Valley, is aware of the fact that we not unfreqnently 

 meet with thin local beds and seams there, containing precisely such a 

 group of fossils, and yet overlaid, where there is not the slightest dis- 

 turbance of the strata, by hundreds of feet of unmistakable coal-meas- 

 ures, filled with their characteristic plants, Foraminifera, Brachiopoda, 

 Lamellibrancliiata, Gasteropoda, Trilobites, fish remains, &c. Hence it is 

 more probable that the association of these ten or twelve fossils in this 

 bed of chert, and the absence, so far as known, of the other forms men- 

 tioned, resulted from some peculiar local physical conditions before, rather 

 than at or after the close of the carboniferous period. The probability is, 

 that this bed belongs to the same horizon as the rocks in Kansas, to which 

 we have applied the name Permo-carboniferous, though it may be even 

 somewhat older. 



The few forms placed in the list under the heading "Jurassic species," 

 nearly all came from the same horizon, and some of them from the same 

 localities, as those we have figured and described in the paleontology of 

 the Upper Missouri, and there referred to the Jura. Although the spe- 

 cies known from these beds are amply sufficient to prove them to be 

 of Jurassic age, they scarcely warrant, or, at any rate, have not yet been 

 sufficiently compared with European Jurassic species to justify a positive 

 opinion in regard to their precise horizon in that great series of rocks, 

 though they appear to occupy a rather low position in the same, judging 

 from their affinities. The single Ammonite from between Sacramento 

 and Summit Station, described by Mr. Gabb, under the name A. Neva- 

 densis, probably came from the horizon of some part of the Ljas. 



The cretaceous species enumerated in the list belong to horizons rep- 

 resenting all of the subdivisions of the cretaceous series as made out in. 

 the Upper Missouri country, and serve to illustrate, to some extent, the 

 geographical extension of these several rocks or groups, southward and 

 westward from the original typical localities. The numbers 1, 2, 3, 4,, 

 and 5, along the right-hand margin of the list, opposite the localities, 

 show to which member of the Upper Missouri cretaceous each species 

 belongs — the subdivisions of the Upper Missouri cretaceous having 

 been severally named and numbered from below upward, as follows : 

 No. 1, Dakota Group ; No. 2, Fort Benton Group ; No. 3, Niobrara Di- 

 vision ; No. 4, Fort Pierre Group, and No. 5, Fox Hills Beds ; the names 

 being derived from localities where the several formations are well de- 

 veloped. 



The specimens from twelve miles southwest of Salina, Kansas, came 

 from a brown ferruginous sandstone belonging to the horizon of the 

 Dakota Group, or oldest division of the Upper Mi ssour cretaceous series.. 

 19 G 



