488 EEPOKT UNITED STATES GEOLOGICAL SUEVEY. 



iferous limestones, while tlie horizon of the Magara is greatly attennated 

 and represented by ordinary limestones difficult to distinguish from the 

 beds which, a little higher up, contain well-recognized Carboniferous 

 fossils. But to whatever period these doubtful limestones belong, there 

 is entire absence of beds of passage of mechanical origin, as arenaceous 

 and argillaceous materials, so that the physical conditions here preva- 

 lent were very different from those that obtained at the close of the Que- 

 bec and Niagara iieriods iu other xDortions of the district. At Station 

 XLIX the lower limestones of the Carboniferous exhibit precisely the 

 same features as mark their occurrence in the Gros Yentre Mountains : 

 lower grayish-drab cherty limestones, with crinoidal remains and a me- 

 dium-sized Orthoceras, succeeded by dark drab and , brown magnesian 

 beds and buff semi-magnesian limestones, and which probably attain an 

 average thickness. 



U]}per Ckirhoniferous. — At least in certain areas of their exposure in the 

 district, the interval between what has been regarded as the top of the 

 lower and the base of the upper series of the Carboniferous is occupied 

 by a set of deposits which marks an abrupt break in the conditions imder 

 which the heavy series of lower limestones was formed, and which were 

 thereafter never fully re-established. In the Teton Mountains this change 

 was, perhaps, most jironounced, and inaugurated the deposition of are- 

 naceous clays, nodular and thin beds of limestone, finished in a heavy 

 bed of reddish-buff' laminated sandstone, and intensely hard, brittle, sili- 

 ceous layers, the general appearance of which might well lead the obser- 

 ver to mistake their probable relationship and refer them to the " red 

 beds" of the Triassic period. The deposit as here developed ranges 

 from 200 to 400 feet in thickness. Eemnants were met with as far north 

 as the great foreland between the West Teton and Bear Creek, but to 

 the south it was seen at several localities fully developed, and the 

 maturer study of the data obtained in this quarter renders almost certain 

 that it properly belongs to the horizon above indicated. The fact of the 

 deposit being finished by hard siliceous ledges has preserved it from 

 destruction over considerable areas in the great foreland south of West 

 Teton Creek, where the superimposed deposits have been swept away, 

 leaving it as a rocky mail i;)rotecting the limestones below. And this 

 office assigned it in the economy, so to speak, of the mountain, where it 

 in places apparently constitutes the deposit overlying the Carboniferous 

 limestones, together with its striking lithological resemblance, renders the 

 determination of its real stratigraphical relations a matter of unusual in- 

 terest and importance. So far as we have been ablef in the course of 

 hastily-executed examinations, to study the true " red bed " series in 

 localities where it exhibits what may be regarded as its typical develop- 

 ment, as well as the subjacent deposits, it has been found to present an 

 entirely different association of features, the consideration of which forms 

 so important a subject of inquiry in the deposits under consideration. 



At the extreme southern end of Teton Eange the section of these beds 

 in the crest of Station XLTII ridge, given iu a preceding page, is suffi- 

 cient, it would appear, to dispel any doubts raised on lithological resem- 

 blances of the actual relations of these beds. We here find intercalated 

 with the red arenaceous shales and ferruginous sandstones layers of 

 limestone which contain the relics of a Carboniferous fauna. And these 

 fossils are not of the types of the latest period or epoch of the series, but 

 are of not later date than the Coal-Measures, if, indeed, they prove 

 not to be identical with Lower Carboniferous forms. The limestones of 

 the latter, which here immediately underlie these passage beds, are 

 charged with corals and other fossils of emiueutly Lower Carboniferous 



