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gradually to subside, and did not cease to diminish
till the basin was left quite dry. 1 had now, however,
an opportunity of taking the dimensions of the
basin and its pipe, the former of which was found
from actual measurement to be fifty-six feet in the
greatest diameter, and fifty-two feet in the narrowest,
and the greatest depth about four feet. The
shaft or tube in the middle, at the upper and
shelving part, was found to be 18^ feet one way,
and 16 feet the other; but it narrows considerably
at a little distance from the mouth, and appears to
he not more than ten or twelve feet in diameter.
^ The Mound, Basin, and Tube o f the Ch-cat Oeyscr.
Perpendicular Section through the mound, pipe, and basin.
I measured its depth on two sid e s: on one
1 found it to he sixty-seven feet, and on the other
a little more than seventy. The sides of the tube
are smoothly polished, probably by the constant
friction of the water, which is also the case with
the floor of the basin, whose surface is perfectly
smooth and even, and has the appearance, in parts,
of agate, and is so hard that 1 was unable to detach
a single piece with a hammer. It is difficult to
imao-ine in what manner this capacious tube, perfectly
perpendicular, has first been shaped, and
equally so how the smooth crust with which it is
lined has been laid on—whether at once, or by
successive depositions of the laminae of siliceous
matter. The lining of the basin or bowl would
appear to be of more easy explanation : the water
remaining therein quiescent may deposit its silica
undisturbed, but in the pipe of the tunnel it is
always bubbling or boiling, sometimes higher,
sometimes lower, .or exploding steam and water.
But after all, that which is the most difficult to
comprehend is this—that the water of the Geyser
is perfectly clear, and gives no deposite without the
application of chemical tests, and then only in the
smallest possible q u an tity : it may be kept for
years in bottles, without depositing the least sediment.
It becomes a question, then, how such a quantity
of siliceous matter is deposited, not only in the
tube and floor of the basin, but also on its rim
or border, which forms the highest part of the
mound. The matter here deposited is abundant,
and appears to he constantly forming; and as this
rim is out of the reach of the hot water except in
one spot, ikwould appear that this deposite is from
the condensed steam or vapour, which is the more
probable from the extreme delicacy of the efflo