132 RECONNAISSANCE FROM CARROLL, MONTANA, 
is said to do, lasted for an hour; the entire volume of water thrown out being very great. At 
length, with a sudden burst, the steam drove up the water to a much”greater height than before 
seen; the noise and concussions accompanying the outburst being very violent. The water 
was kept at its greatest height for two or three minites, and for this time we found the Giantess 
all that had been claimed for it. But the reservoir was almost exhausted, and in a short time the 
only escape was a mass of steam, which rushed out of the crater with a force which no words could 
describe. 
After we bad become somewhat accustomed to the noise of the eruption, and the awe inspired 
by the vast outburst of steam had in a measure subsided, we experimented upon the violence with 
which the vapor was ejected by throwing into the crater trunks of trees, logs, and other objects 
which could be found near at hand, and the height to which these were thrown by the escaping 
steam was a good indication of the force which was being expended. The heavier of these objects 
Sank nearly to the narrowest part of the crater, and after being held for a moment suspended at 
this point, rising and falling, according to the violence of the jet which they met, were swiftly shot 
forth, often rising to a very great height. 
This steam escape lasted for an hour without any sensible diminution in violevce, and we could 
not help regretting that all the water had been ejected before the most powerful burst of steam 
had begun, so that we might have had a full display of the power that was at hand acting on the 
water. The conception of force given by this great steam escape was perhaps even greater than 
if it had taken merely the form of a fountain. Six hours later the steam was still escaping, though 
with somewhat diminished energy, and an occasional liquid jet seemed to show that a little water 
was draining into the reservoir, only to be immediately ejected. 
This great steam escape is important as bearing upon the general subject of geysers, showing 
the vast amount of steam which must be accumulated before the discharge can take place, and the 
high tension under which it must be. 
The Castle Geyser was active most of the time during our stay, though with varying force. 
The amount of water discharged was never very large, and the highest jets did not exceed 50 
feet. 
The Grotto was also almost continuously active, and after seeing the injury done to its crater 
by visitors, the large majority of whom are residents of the Territory, we could not help wishing 
that the discharge of boiling water were absolutely continuous, so that the depredators might be 
kept at a respectful distance. 
The Saw-mill Geyser played frequently at short intervals, but quite irregularly. 
The Giunt was quiet, occasional spirts of water to the top of the crater being the only sign of 
latent energy. 
GENERAL CONCLUSIONS. 
DISTRIBUTION OF THE FORMATIONS. 
Pre-Silurian rocks.—Up to the time when we reached the second Yellowstone Caiion, we had 
seen absolutely nothing of any rocks older than the Primordial series. This is true, not only with 
respect to our observations, made in the several minor ranges of mountains, but also includes the 
inferences to be drawn in regard to the elevated points not reached, from the absence of any 
crystalline rocks in the local drift. The only exception to this was at Camp Baker, where the drift 
contained such masses, doubtless from the neighboring Big Belt Range, which we were unable to 
visit, but in which we should expect to find a considerable development of the Pre-Silurian series. 
Granitic rocks have been observed by others on the east side of Gallatin River, but they did 
not appear within the limits of our observations. The inferred absence of crystalline rocks from 
the minor ranges of hills, which break through the prairie at different points in this part of Mon- 
tana, for example, the Judith Mountains, the Snow Mountains, Little Rocky Mountains, ete., if 
correct, would make it improbable that ore deposits of any economic value should be found in 
them. 
Silurian.—Primordial series.— We observed strata, proved by fossils to belong to the Potsdam, at 
two localities, and the relations of the rocks at these points as far as made out have been described ; 
they may, however, conveniently be recapitulated here. 
& 
