'i(>4 CARBONIFEROUS FORMATIONS AND FAUNAS OK COLORADO. 



lowt'i- ill Iho liods ol' the oilier areas, and a riiuiial change of about the same \iihn' 

 separates it from the fauna of tlie middle Ilermosa. This last is, liowever, pai'tly due 

 to the fact that the fauna of the lower Ilermosa was in almost every case found at the 

 base of the series, with a considerable thickness intervening- between it and thefossil- 

 ilVrous horizons ol' the middle Hermosa. If tiic Wel)er limestone and ihc Maroon 

 formation were not deposited consecutively, it is probable that a similar interruption 

 intervened between the lower and the middle Hermosa. This does not, however, 

 seem to tind support from observations in the field, and it is important to iiiark that 

 in a numerical expression the fauna of the lower Hermosa is but little more different 

 from that of the middle than is the middle from the upper division, though certain 

 features of the brachiopod representation give it a more distinct facies. 



With regard to the age of the Penusylvanian formations of Colorado compared 

 with the better-known sections of the Mississippi Valley, I believe that the Hermosa 

 formation, the Weber and the lower Maroon formations, and the Weber shale and 

 Weber grits come very early in Pennsylvanian time and are probably older than 

 any beds of the Kansas and Nebraska sections. The opinion that these formations 

 represent verj^ early Pennsylvanian time is supported by the fact that a number of 

 species, as, for example, Productus gallatinensis, and especially' the Bryozoa, are 

 either identical with Mississippian forms or closely related to them. The belief that 

 these formations are older than the oldest beds of the Kansas section, or at least are 

 to be correlated with them, finds support not only in the same facts, joined to this 

 other, that apparently a long period of early Pennsylvanian time is unrepresented in 

 the Kansas section, but also from the following considerations, manj^ others similar 

 to which could probably be mentioned. The genus Meehella occurs in the Fort 

 Scott limestone (2) " almost at the base of the Kansas section, while in Colorado it is 

 known at but two localities and is not very characteristic. Enteletes, which is 

 abundant well down in the Kansas section in the lola limestone (16), is not known in 

 Colorado, except at one locality, Sinbads Valley, whose horizon is supposed to be in 

 the Hermosa formation, but higher than any of the Hermosa beds of the San Juan 

 region. Chonetes mesolobus is abundant in Colorado, but is restricted to the early 

 portion of the section in Kansas, extending no higher than the Parsons lime- 

 stone (6). The same is true of Chonetes fiemingi, which is abundant in Colorado, 

 and though having a long range in Kansas seems to be the ani^ecedent type of Ch. 

 firnnnlife7\ which does not make its appearance until about the Lecompton lime- 

 stone (22). This species is not known in Colorado except at Sinbads Valle}', where 

 its horizon appears to be considerably above the top of the Hermosa formation in 

 the San Jnan. Productus sem.ireticidatiis \?i\\ lierniosamis, which distinguishes the 

 upper divisions of the Hermosa formation, is found, only in the lower portion of the 



a The numerals refer to the beds in the general section of Upper Carboniferous rocks of Kansas. 



