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X/ ’ /- -^THE SCIENTIFIC MONTHLY. 525 
miles from Madisor/ Lake. This spring, which throws the water to a height of 
285 feet in an immense solid column, is one of the grandest sights of nature. The 
orifiice of its tube is encircled by a rim or bank ten feet high. 
Prof. Tyndall speaking of the Great Geyser of Iceland says : ‘‘It consists of 
a tube seventy-four feet deep and ten feet in diameter; the tube is surmounted 
by a basin which measures from north to south fifty-two feet across, and from east 
to west sixty feet. The interior of the tube and basin are coated with a beautiful 
smooth silicious plaster, so hard as to resist the blow of a hammer; and the first 
question is, how was this wonderful tube constructed—how was this perfect 
plaster laid on ? Chemical analysis shows that the water holds silica in solution, 
and the conjecture might therefore arise that the water had deposited the silica 
against the sides of the tube and basin, but this is not the case, the water deposits 
no sediment; no matter how long it may be kept, no solid substance is separated 
from it. It may be bottled up and kept for years as clear as crystal without 
showing the slightest tendency to form a precipitate. To answer the question in 
this way would moreover assume that the shaft was formed by some foreign 
agency, and that the water merely lined it. The geysers basin, however, rests 
upon the summit of a mound about forty feet high, and is evident from mere 
inspection that the mound has been deposited by the geyser; but in building up this 
mound the spring must have formed the tube which perforates the mound, and 
hence the conclusion that the geyser is the architect of its own tube. 
“ If we place a quantity of geyser water in an evaporating basin the following 
takes place; In the center of the basin the liquid deposits nothing, but the sides 
where it is drawn up by capillary attraction, and thus subjected to speedy evapor¬ 
ation, we find silica deposited. Round the edge a ring of silica is laid on, and 
‘^not until the evaporation has continued a considerable time do we find the slightest 
turbidity in the middle of the water. 
“This experiment is the microscopic representative of what occurs in Iceland, 
Imagine the case of a simple thermal silicious spring, whose waters trickle down 
a gentle enclosure, the water thus exposed evaporates speedily, and silica is 
deposited. This deposit gradually elevates the side over which the water passes 
until finally the latter has to take another course. The same takes place here, the 
ground is elevated as before, and the spring has to move forward. Thus it is 
compelled to travel round and round, discharging its silica and deepening the 
■ shaft in which it dwells, until finally, in the course of ages, the simple spring has 
produced this wonderful apparatus which has so long puzzled and astonished both 
the traveler and the philosopher .”—Wonders of the Yellowstone. 
“ The time required for the construction of the Great Geyser has been esti¬ 
mated by Commander Forbes as ten or eleven centuries, on the following grounds: 
A bunch of grass, placed finder a little fall made by the ejected water, receives, 
in twenty-four hours, a coating of silica the thickness of a thin sheet of paper, or 
about one five hundredth part of an inch. At this rate it would take 1036 years 
to build up the 762 inches, which, according to his measurement, is the depth of 
the tube. In evidence of the probable truth of this estimate, he makes note of the 
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