438 EEPOET UNITED STATES GEOLOGICAL SUEVEY. 



otlier manifestations apparently of more or less local character, as tlie 

 change in the strike from the general northwest and southeast direction 

 to courses east-west and north-south. Beyond this point the Carbon- 

 iferous deposits are boldly upraised, and thence to the debouchure of the 

 canon, a distance of some ten miles, they constitute the mass of the 

 caiion-walls. 



The above recapitulation of the Grand Cainon section has been intro- 

 duced to facilitate the comparison of the interesting region it traverses 

 with the region visited along the northeastern flank of the same range 

 of mountains. It will be observed that Professor Bradley notices a 

 heavy series of sandstones and siliceous deposits making up the lower 

 half and more of the Carboniferous series in this quarter, where the 

 upper deposits are almost entirely composed of limestones. This shows 

 a striking change in the character of the earlier sediments of the Car- 

 boniferous period in this quarter, especially as compared with what ob- 

 tains in the Teton Eange, where the lower beds are mainly calcareous. 

 It is possible that the section in the Grand Canon does not retain the 

 ux)permost deposits, which, as we have already seen in the region of the 

 Pierre's Mountains, are usually made up of alternations of heavy beds 

 of hard sandstone and limestone layers. The great breadth over which 

 the Carboniferous beds outcroi:) in the Grand Caiion also offers some- 

 thing strongly in contrast with their apjjarent limited occurrence in the 

 barrier ridge along the lower valley of the Snake in the northwest con- 

 tinuation of the same range. But this state of things may meet Avith 

 satisfactory exi^lanation in the fact that, in the process of excavation of 

 the lower valley, a vast mass of their strata has been removed, the valley 

 gradually widening and encroaching more and more on the Carboniferous 

 belt in its progress to the northwest, in which latter quarter it has left 

 'a narrow remnant-stri]3 on the southwest side of the valley, while above 

 the entire area of the belt is confined to the Snake Eiver Eange where, 

 in the vicinity of the Grand Caiion, it maintains its original breadth. 

 The Carboniferous axis in the eastern flank of this range is not recog- 

 nizable in the caiion section, which, if it extended so far to the south- 

 east, probably gained the upper valley of the Snake above the Grand 

 Canon. It is much more difficult to correlate the red sandstones and the 

 gray and green sandstones which comj)ose the rocks for the first few 

 miles on entering the caiion from above. Professor Bradley's descrip- 

 tion of the lower gray and green sandstones and calcareous shales an- 

 swers well the appearance of a heavy series of strata which occupies the 

 little basin area at the northeast extremity of the Pierre's Mountains, 

 w^here very similar beds are associated with Jurassic deposits, but so 

 inextricably confused as to involve their relations to the latter formation 

 in much obscui?ity. But, on lithologic grouuds, the deposits at the latter 

 locality were compared with the Laramie beds, and it may further be 

 observed that the latter formation, as here defined, also holds extensive 

 deposits of red sandstones, and it is possible that the beds noticed by 

 Professor Bradley belong to this early Cenozoic grou]i. In the event of 

 the confirmation of the latter supposition, may not these exposures in 

 the upper portion of the Grand Caiion belong to the series of gray and 

 buff and red strata which appears in the broad belt stretching across 

 this highland region between the southeast flank of the Stations XXXIX 

 and XLIl ui^lift and the great Carboniferous barrier ridge along the 

 lower vaUey of the Snake ? 



PIERRE'S BASIN. 



The bay-like recess known as Pierre's Hole or Basin occupies the in- 

 terval between Teton Eange and the Snake Eiver Mountains, and com- 



