118 RECONNAISSANCE FROM CARROLL, MONTANA, 
The road from Moss Agate passes, it is true, more or less at the end of the bills, but at such 
a distance from them as to afford but little opportunity for observation. From a distance, it is 
observed to how great an extent the hills are made up of limestone, with the conspicuous trachylic 
prominences before mentioned. From the limestone, we pass immediately to a dark, somber sand, 
stone of granular texture and quite peculiar in appearance. This had a dip to the west, and con- 
tained some indistinct plant-remains. 
On our return journey, we found time to touch at the southeastern extremity of the same hills 
near the source of Flathead Creek, and here we passed directly from sandstones resembling the 
one spoken of to the limestone exactly similar to those so often observed at various points in this 
range. It agreed in all respects with the other exposures. A few indistinct fossils were obtained 
from a loose block, which had evidently come from close at hand, and these show it to be Carbon- 
iferous. They were identified by Mr. Whitfield as Spirifera centronata, Winch. 
The country near the branch of Deep Creek on the south side of the Elk Range is attractive 
and covered with good grass, supporting large herds of cattle; but, after passing the low divide which 
separates the above-named streain, a tributary of the Missouri, from Shields River, a branch of the 
Yellowstone, a more or less decided change is observed. The prairie is here dry and barren, espe- 
cially to the south of Cottonwood Creek, and supports nothing but a thick growth of sage-brush. It 
is watered by several running streams beyond Sixteen-mile Creek, of which Cottonwood is one of 
the most important, in view of the fact that its banks are fringed with fine trees, from which 
it takes its name. 
As we approach Bridger’s Pass, the character of the country improves again, and the large 
numbers of cattle met with near this point indicate its capabilities in the way of grazing. Of the 
geological relations of this part of the road, we saw little on our way south. While returning, how- 
ever, our opportunities for observation were better, and the results are presented immediately below. 
Bridger Pass is a high mountain-divide, thickly wooded, and with the high limestone cliffs of the 
Bridger Mountains overhanging it on the west side. The scenery is fine, and the change from the 
bare prairie to the grateful shade of the wooded mountain-side is gladly weleomed by the traveler 
Geologically speaking, the prevailing rock is the dark sandstone described later, and known to 
belong to the Upper Cretaceous. The position of the strata is nearly vertical. An occasional dike 
of igneous rock was observed, and one of these was conspicuous on the north side of the pass. It 
consists of a greenish basalt in spherical nodules, separating in the fracture into successive thin 
slabs. High above the road,as we approach Fort Ellis, we noticed the horizontal strata of the 
Pliocene Tertiary, which, according to Hayden, extends far away toward the west.’ 
From Fort Ellis, the party extended their trip into the Yellowstone Park. We introduce here, 
however, the additional observations made on our return-trip through the country just mentioned. 
BRIDGER MOUNTAINS. 
On our return to Carroll from Fort Ellis, early in September, we encountered much trouble at 
first from the condition of the roads, which were almost impassable, owing to the unprecedented 
amouut of rain that the country had recently received. We made use of the delay which this occa- 
sioned in the movements of the wagons, to make a little exploration of‘ the Bridger Mountains, or 
East Gallatin Range, as it is sometimes called. These observations could not be extended beyond 
the east side of the range, and hence are only fragmentary. Considerable time was devoted to the 
same mountains by Dr. Hayden and his parties in 1871 and 1872, and reference may be made to his 
reports for those years for the facts observed by them. 
This range of mountains is especially conspicuous as viewed from the east side, rising up steeply 
from the deep and narrow valley, and terminating in a nearly perpendicular white wall, with a 
sharp knife-edge for its summit. We ascended the ridge from two points: first, September 4, from 
a point in the valley below, about six miles from Fort Ellis; and, again, September 5, from our 
camp, a short distance to the north side of the divide in the Bridger Pass. 
The rock of the valley, and indeed of the pass, as far as observed, is a sandstone of somber 
tints, gray, brownish, or greenish. The texture is generally granular and gritty, and the rock is 
more or less speckled with grains of quartz and feldspar. In general, it may be said to be a sand- 
