68 Mr Fox on Springs of Water. 
specific gravity, must always tend to raise any spring-water with 
which it may be connected, to a higher level than itself. He caleu- 
lates that sea-water 4 miles deep, of the mean temperature of 60° 
for the whole depth, and specific gravity 1.027, would balance a co- 
lumn of spring-water at 200° of temperature, of more than 4 miles 
and 1200 feet deep; and 1200 feet of spring-water are equivalent 
in weight to-450 feet of granite. 
In this calculation he has made a large allowance for impurities in 
solution in the spring-water, tothe extent of one-third of the propor- 
tion of salt in sea-water, which is at least five times as much as the 
average state of water taken from the lowest parts of many of our 
deepest mines would require; and he has assumed the column, de- 
scending 4 miles deep in the earth, to have a mean temperature 
of only 200° ; whereas, according to the first table, the temperature 
stands at 490° at that depth, which would give a much higher mean, 
and more than he is prepared to admit, for the reasons already given. 
There may be a large proportion of sea-water at great depths in the 
earth; but a column of this 4 miles deep would be expanded to about 
850 fect more, if its temperature were raised from 60° to 200°. 
It is not to be supposed, he adds, that such great effects will any 
where be seen, because of the vents which the heated water would 
find. at lower levels; even at the bottom of the shallow seas these 
vents may be sufficient, in most instances, to take off any pressure 
tending to raise the fresh-water ashore. It will be readily granted 
that salt water may ooze through the deepest beds of the sea, or, in 
some parts of these, flow into the earth in greater or less quantities, 
according to the greater or less resistance it meets with at its en- 
trance, or in its subterranean course. The numerous veins of clay 
which intersect the crust of the earth, must present formidable ob- 
stacles to its rapid progress ; and it cannot advance under ordinary 
circumstances without displacing other water, which can only be 
done in proportion as the latter finds means of escape. It is evident 
that at the bottom of seas of inferior depth, the balance must be in 
favour of the upward pressure, for even if the water be as salt as 
that of the ocean, at considerable depths below its bed, its specific 
gravity will be diminished by the expansive influence of the subter- 
ranean heat, so that it will yield to the superior pressure of the 
colder sea, and escape wherever it may find the resistance the least ; 
this may, in some instances, be through fissures communicating with 
the shore, or under nearly horizontal beds of clay through which it 
cannot find an upward vent till it reaches land, and there, under 
such circumstances, it might produce springs more or less elevated 
above the surface of the sea. The force with which the water in 
Artesian wells sometimes gushes up from great depths, shews us 
how tenaciously the fluid must be confined down by the superin- 
cumbent strata; and the bed of the ocean is also commonly sup- 
posed to be for the most part very impermeable to water. Mr Fox 
