130 RECONNAISSANCE FROM CARROLL, MONTANA, 
rock is remarkable for its very porphyritic character ; the crystals of orthoclase being very numer- 
ous and of considerable size, a quarter to half an inch in length. They are usually more or less 
altered, and under the microscope prove to be made up of minute crystals apparently of a triclinic 
feldspar, the base consisting of the same material. The whole rock is very white on the fresh 
fracture; but the little iron it contains oxidizes on expostre, and the surfacebecomes rusty. 
Descending the hill, we pass south over the terrace mentioned before, which would give a good 
section of the rocks to one who had the time to examine it with care. The lower portion of the 
southern face of the hill is precipitous ; the trachyte showing a bold front. Passing from the talus 
of the mountain, we came upon a series of variegated shales, mostly bright-red, also greenish and 
blue, evidently baked by the eruption of igneous rock close by; occasional beds of red sand-rock 
and mud-shales occur with the others. The general strike is shown on the map. The total thick- 
ness of these sbales was some 800 feet; no fossils were found, only a few indistinct vegetable 
remains. Overlying these shales,with a slight change of strike, was a thick-bedded sandstone 
honeycombed, and in other respects so similar to that described as occurring at a, that the identity 
of the two can hardly be doubted; the underlying shales also correspond. From this point south, 
the dip became more and more gradual, the terraced hill more grassy, and at d, perhaps two miles 
from the hills, the dip is reversed, and the sandstone of a and e appears with a slight northerly 
dip. Still farther south and west, the hills are more broken, and we passed over a series having a 
somewhat different strike, consisting of a sandstone, then black shales containing large concretions 
with selenite plates; and, overlying this, other sandstone layers. This shale suggests strongly the 
Fort Pierre Group, which is seen horizontal only a few miles distant on the prairie. Other expos- 
ures of sandstone, yellow and granular, were noted at points to the south (see figure); they had a 
strike and dip as shown in the sketch. These latter are exceedingly similar to those which yielded 
No. 5 fossils at Box Hilder. No fossils were found, however; though it cannot be doubted that the 
series of rocks belongs mostly to the Upper Cretaceous. Tnough has been said to show, with the 
help of the sketch, that the relations are by no means simple. In general, it may be said that the 
hills, at least at this point, give evidence of folding; the axis lying east and west, so that the uplift- 
ing force must have been from the south. Our return trip was made by the same trail, and admit- 
ted of no further observations. 
VHE GEYSERS OF THE YELLOWSTONE PARK. 
The route followed by the party in going from Fort Ellis to the Yellowstone Lake and Geyser 
Basins and returning was that generally taken from this point: through the cation of the East 
Gallatin River and down the valley of Trail Creek to the Yellowstone River, thence up its valley 
to the Mammoth Hot Springs, and hence to the falls, the lake, and the geysers. This route has 
been twice explored by Dr. Hayden and his parties in 1871 and 1872, and the objects of interest in 
the park have been described in addition in the valuable report of Captain Jones and Prof. Com- 
stock, who visited it in 1873. It was not to be expected, therefore, that our hurried trip of nine- 
teen days from Fort Ellis and return would give us any opportunity to collect any important 
additional facts. 
It therefore does not seem to us desirable to attempt here an account of the somewhat discon- 
nected observations we were able to make on our very rapid journey from Fort Ellis to the Geyser 
Basins, as they must be, in a great measure, repetitious of what has been already published. We 
may remark, in passing, upon the very great beauty and interest of the whole region, and the 
wonderful field that it offers for the study of all kinds of modern volcanic rocks. 
It seems, however, that it may be of some little interest to record the action of the more 
important geysers as observed by us during the day or two which we spent in the basins. We do 
this, not imagining that the facts in themselves have any especial importance, except so far as this: 
that the more the facts in regard to the geysers and their operations are accumulated and recorded, 
the better will ultimately be the understanding of the phenomena involved. 
We reached the Lower Geyser Basin the evening of August 20, and, having at that time and 
during the following morning but a few hours of daylight in all, we saw no display from the more 
prominent of the geysers of this basin. The only particularly noticeable eruption observed by us 
