TO YELLOWSTONE NATIONAL PARK. V1 
These beds bend around some 50°, so that in a vertical section they describe a quarter circle. 
The upper and central part of the hill consists of limestone, overlaid by a considerable thick- 
ness of slates and sandstones, dipping mostly east-southeast. The hill alluded to forms the 
extremity of this portion of the Little Belt Mountains. Farther along to the west, in the main 
range, is a limestone which has every appearance of dipping under all the rocks thus far men- 
tioned ; it probably corresponds to the firm limestone which forms the lower portion of the Carbon- 
iferous as developed in this region. The structure of this hill, thus imperfectly made out (a hasty 
run across it while the party was going round being all that circumstances admitted of), may be 
better understood upon the statement that it is an anticlinal fold; the axis pointing about north 
30° west, and somewhat elevated in this direction. The south side of the fold is apparently the 
steeper. 
JUDITH GAP TO THE MUSSELSHELL CANON. 
From the Judith Gap to the Musselshell Cafion, a distance of rather more than forty miles, 
the underlying rock belongs for the most part to the Upper Cretaceous; the only fossils found hav- 
ing been referred by Mr. Whitfield, as stated below, to No.5. his district is remarkable, perhaps 
more so than any other seen by us, for the deep and wide valleys which have been cut through the 
nearly horizontal rocks, and which lead away from the neighboring range, the Little Belt Mount- 
ains. There are now no streams running from the mountains, with the exception of Haymaker’s 
Creek near the Forks of the Musselshell, and yet the otherwise remarkably level prairie is broken 
by a number of striking ravines or valleys. These are all alike in that they show no evidence of 
any important action by recent running water, but, on the contrary, point to agencies which must 
have done their work in glacial times. The beds of these valleys, and also, though to a less 
extent, the prairie above them, are strewn with pebbles and masses of limestone, whose source is 
in the monntsing, only a few miles distant. 
Three very conspicuous valleys, one of them a mile wide, with ‘steep banks more than one 
hundred feet in height, are crossed before going twelve miles from the gap. Hopley’s Hole is by 
far the most remarkable of these. A section is given in the following cut (fig. 8). 
\ 
Fig. 8. 
Sandstone. 
ines. eT 
A Section across Hopley's Hole. 
The width of the coulée at the top is about 1,000 yards. From the level of the prairie on 
either side, there i is a steep plunge down; the total depth to the dry bed of the little stream being, 
according to aneroid measurements, 150 feet. On the west side, a second terrace of 50 feet in 
height is very distinct, while on the eastern slope a similar terrace, at about the same height, seems 
to be indicated ; at present, however, there remains only a series of little conical hills all lying in 
a continuous fine and presenting quite a peculiar appearance. This ravine is now dry, with the 
exception of a few springs of moderately good water on the west side. The water from these springs 
moistens the ground for a little distance about the point where they appear, but soon sinks out of 
sight. In the early part of the year, after the melting of the snow, more or less water evidently runs in 
the bed of the stream, which is dry in summer; but its erosive power is small, and there is nothing in 
the present relations which will explain the existence of such an extended valley. Hopley’s Hole is 
important to those who pass over this road, not only as furnishing one of the few sources of water in 
this part of the route, but also because along the eastern edge of the valley there is here and there a 
little timber ; a few straggling pine-trees which have ventured out into the prairie from the adjoin- 
ing hills, and which show, by their appearance, that they have here a hard struggle for existence. 
The western slopes of this ravine, over which the limestone pebbles before mentioned are thickly 
scattered, are more gradual than the eastern; and, while the former are covered with thin grass, the 
latter shows a line of exposure of the sandstone which underlies the level prairie here. The upper 
