246 CAKHONIKKROUS FORMATIONS AND FAUNAS OK COLOKAIXi. 



pro\'i()iis studies had licrii made and (ncr wliicli llii' saiii(> foriiiatioiis extend witli 

 onlj' local variations. They recognized two foiinatidiis of Upper CarboniferouH age, 

 the Herniosii and (lie Rico formations; ])ut C'l'oss has recently discriminated a tliird, 

 the Molas formation, which is a thin stratum of red shale intermediate between the 

 Herniosa formation and the Onray limestone. 



The Molas formation is best known in tlie Needle Mountains quadrangle, where 

 it has a thickness of only about 75 feet. It is a series of shales, but contains bands 

 of diverse texture and material, among them being some of impure limestone 

 and .some sandy. The color is an intense red, often strongly mottled with lighter 

 tints, which occasionally are nearly white. It contains pebbles and small bowlders of 

 chert, some of them fossiliferous. The fossils are the same species which occur in 

 the Mississippian fauna of the upper part of the Ouray limestone, where the cherts 

 without doubt had their origin. The base of the Molas often contains bowlders of 

 Ouray limestone of considerable size. The upper surface of the Ouray is more 

 or less stained with the Molas, whose material and color appear to have worked 

 down into cracks and crevices between partly loosened blocks of the older formation. 

 Some of the impur(> limestone beds of the Molas are fossilifei'ous. The collections 

 so far, obtained from the formation are but 3 in number, with a total of 6 species. 

 The stations are iilSti. 2187, and 2188. 



The Hermosa formation consists of limestones, shales, and sandstones, and has 

 a maximum thickness of 2,000 feet. Its characters are very inconstant, and while 

 a threefold division was made in the Rico region, by reason of the segregation of 

 the limestones into the middle portion, this could not be eflected satisfactorily else- 

 where. The lower division, composed mainlj- of shales, is, roughly speaking, 700 

 feet in thickness. The central division, or heavj"^ limestone series, is 500 feet thick, 

 while the upper or transition member, of sandy and limy shales, is about 800 feet 

 thick. In all, 71 collections were obtained from the Hermosa formation, and most of 

 them have been located in one or another of the three stratigrajihic subdivisions. The 

 following stations are located in the lower series: 2197, 2198, 2209, 2213, 2214, 2247, 

 2279, and 2284. In the middle series are the following stations: 2202, 2211, 2212, 

 2217, 2220, 2222, 2223, 2224, 2225, 2228, 2229, 2236, 2236, 2237, 2246, 2249, 2282, 

 2286, 2287, 2301, 2332, 2333, 2334, and 2335; and in the upper series are the follow- 

 ing: 2200, 2201, 2203, 2204, 2205, 2207, 2208, 2210, 2216, 22}8, 2219, 2221, 2226, 

 2231, 2232, 2238. 2239, 2240, 2241, and 2283. 



Upon these stratigraphic subdivisions and upon the collections designated is 

 based the following tabular statement, which shows the distribution of the Molas 

 and Hei'mosa species by localities and in the final three columns their vertical range. 

 Details of local representation, distribution, and range can, therefore, be secured 

 from this source and from the register of localities appended. 



