560 R. T. CHAMBERLIN 
penetrate the porous cylinder readily, evaporating and leaving its 
dissolved material within the mass of the sandstone, and escaping 
as steam on the farther side. The rate at which the water passed 
through the sandstone at the outset was not determined, but after 
5 liters of lake water had been used, it was found that 129 cubic centi- 
meters traversed the rock and were condensed in one hour. The 
rate slowly fell as the experiment progressed. While the thirteenth 
liter was being used, only 73 cubic centimeters passed through the 
sandstone per hour. It was evident that the pores were becoming 
clogged, but to complete the experiment with Lake Michigan water, 
which contains only 150 parts of solid matter per million, would have 
required too much time. ‘To hasten the process, a saturated solution 
of calcium sulphate was substituted. This soon caused a marked 
slackening of the passage of water through the rock, and doubtless 
would have sealed the pores completely, if allowed sufficient time. 
From this experiment, it appears certain that water, evaporating 
in the pore spaces of a rock and escaping as steam, will leave behind 
whatever material is in solution, until the crevices become clogged 
and the penetration of water ceases. ‘This principle may be applied 
to the outer 6,900 feet of the earth’s crust; in the superficial portion 
of this zone it should be very effective, since the conditions more nearly 
approach those of the experiment; in the lower portion of this belt, 
as 6,goo feet and the critical pressure (as well as temperature in the 
neighborhood of hot volcanic pipes) is approached, the density, and 
hence the solvent powers, of the water vapor approach those of the 
liquid. Toward the critical point of water, therefore, the applica- 
tion of this principle becomes more uncertain, but it would seem 
to be operative also at these depths, though more and more slowly 
as the critical point is neared. 
It might be objected that the passage of water into vapor, involving 
the latent heat of steam, would keep the adjacent rocks cool and 
cause the deposition to take place at the very contact where the hot 
lava could fuse, and dissolve, the precipitated salts. But it is very 
doubtful whether the vaporization of such a small quantity of water, 
taking place with the slowness imposed upon it by the minuteness of 
the capillary pores, would keep the contact rocks at a temperature 
below 365°. The gap between 365° and 1,100° is too great for there 
