288 GEOLOGICAL SUKVEY OF THE TEEEITORIES. 



"have reason to believe that there are, however, in the region of the Great 

 Salt Lake, beds representing some of the higher members of the lower 

 carboniferous series of the Mississippi Valley. Colonel Simpson brought 

 from there, in a dark, very hard limestone matrix, specimens of one of 

 those curious, screw-shaped Polyzoa, known by the generic name Archim- 

 edes, so common in the lower carboniferous limestones of the Western 

 States, but unknown in the coal measures. Some of the corals brought 

 by Colonel Simpson and others are also unlike any of those known in 

 the coal measures of the Mississippi Valley, and more nearly allied to 

 forms found in the upper members of the lower carboniferous lime- 

 stone series in the States east of the Rocky Mountains. * 



Among all of the carboniferous fossils yet brought from any part of 

 the Rocky Mountains, as well as from localities west of there, I have 

 never seen a single species indicating the existence there of any repre- 

 sentative of the Burlington limestone, which, with its great profusion 

 of beautiful crinoids, forms so marked a horizon in the carboniferous 

 rocks as developed in some of the States farther eastward. This, how- 

 ever, is just what we might expect, since the Burlington limestone, even 

 in the States alluded to, is comparatively limited in its geographical 

 range, and evidently owes its origin to local physical conditions ; while 

 the Chester, St. Louis, and Keokuk limestones have a much wider geo- 

 graphical range in the Mississippi Valley, and hence would be more apt 

 to be represented at these distant western localities. 



Judging from the few fossils yet brought from the far West that be- 

 long to. the lower carboniferous, the evidence seems to favor the con- 

 clusion that the rocks from which they were collected rather represent 

 the Chester and St. Louis beds than any of the older divisions. It is 

 not improbable, however, that when the whole series of carboniferous 

 deposits in the Rocky Mountains can be thoroughly worked out in detail, 

 there may be found subdivisions there that have no representatives in 

 the Mississippi Valley, as we have reason to believe several members of 

 the series, as made out in the latter districts, may be wanting farther 

 westward. So far as yet known we have no reason to believe, from any 

 paleontological evidence, that the important oldest member of th,e car- 

 boniferous, known in Ohio as the Waverly group or series, occurs in the 

 Rocky Mountain region. 



The small collection of fossils I have placed in a separate list, under 

 the heading " Permo-carboniferous,' 7 are contained in a brittle, whitish, 

 cherty matrix from Box Elder Station, on Platte River. Although 

 without exception, so far as they can be identified, forms that have an 

 extensive range in the coal measures of the Western States — most of 

 them even extending into the middle and lower coal measures, and one 

 even into the Chester limestone* — these fossils, when viewed together 

 as a group, point to a higher position in the series than those that pre- 

 cede them in the following lists. Indeed, there are probably few Euro- 

 pean geologists unacquainted with the range of these forms in the 

 carboniferous rocks of this country, that would hesitate to refer them to 

 the Permian. The genera Pseudo-monotis (Monotis of some, not of 

 Bronn) and BakevelUa are generally regarded in Europe as characteristic 

 of the Permian, while the ScMzodus, Myalina and Pleurophorus, particu- 

 larly the former two, are specifically closely allied to foreign Permian 

 types. The fact, too, that we find among the specimens from this chert 

 but one species of the BracMopoda (Hemipronites crassus) so very com- 



* I have recently identified Hemipronites a-assus, from specimens showing- both the in- 

 ternal and external characters, among some collections sent to me from Professor 

 Stevenson from the Chester limestone of West Virginia. 



