36 WILLIAM H. PICKERING 
at a depth of from 20 to 25, or possibly to 30 miles, in the crust of 
the Earth.”’ The total thickness of the crust has been estimated 
by Fisher’ at 30 miles. These values agree very well with that just 
computed from the volume of the Moon. 
Daubrée has shown? that water separated from a chamber filled 
with steam at a temperature of about 160°C. by a close, fine- 
grained sandstone, passed through the slab with ease, against the 
outward pressure of the steam. He also found that the facility with 
which the water found a passage was increased by heat. There 
is therefore no difficulty in understanding the transmission of water 
through hot rocks at considerable depths. Its presence, moreover, 
would tend to lower the melting-point of the rock, and make it more 
VISCOUS. 
A certain amount of water may even be transmitted in this manner 
down through the ocean floors; but when we consider that the 
transmitting medium consists of cold rock several miles in thickness, 
the water advancing against a constantly increasing pressure, it 
does not seem that the amount transmitted per year in this manner 
can be very large. 
In our hypothesis explaining the origin of the continents, it was 
stated that they were composed of the crust which was either originally 
solid or else had already cooled sufficiently to become so. They 
had therefore expelled a large part of any water which they may 
originally have contained. The ocean beds at the time of the great 
catastrophe were liquid. They therefore absorbed all the water 
available, if indeed they were not already saturated with it. They 
had a much higher temperature, having come from a greater depth, 
and contained much more water at this period, than the continents, 
and, it is believed, have been giving it out as they cooled ever since. 
Doubtless the hot bases of the continents have absorbed some 
water from the ocean beds as the latter cooled, and the expansion 
and diminished, specific gravity thus caused would tend to elevate 
them in the vicinity of the oceans. This has occurred notably in 
the vicinity of the Pacific, the whole of whose coasts are at the present 
time in a state of elevation. We can understand also that the sys- 
t Milne, Sezsmology, p. 120. 
t Geological Experiments, Vol. I, p. 237. 
