APPENDIX—GEOLOGICAL SURVEY. 
401 
Other observations on the temperature of the water from deep-seated and 
hot springs, and from artesian wells fully confirm the experiments made 
in mines, and show that the temperature of the water furnished by them also 
becomes higher in proportion to the depth of the source from which it is 
derived. 
“ As might naturally be expected, the interference of local causes ren¬ 
ders it a matter of considerable difficulty to determine the true mean, gen¬ 
eral rate of such increase in temperature of the earth’s substance down¬ 
wards; still, in the main, observers all agree in placing it at somewhere be¬ 
tween li<j° &nd 2 %° F. for every hundred feet in depth, so that we cannot 
be far wrong, if for our purpose we estimate it at 2° F. for every hundred 
feet in depth, or a rate which amounts to 121° for each geographical mile 
nearer the earth’s center. Since no facts are at the present time known 
which can in any way invalidate the supposition that this, or a somewhat 
similar rate of increase in temperature holds good in still greater depths, it 
is perfectly correct and justifiable reasoning to assume that such is actually 
the case, and therefore a simple calculation will show that at a depth of 
about twenty-five geographical miles from the surface downwards, a tem¬ 
perature of about 3,000° F. should be attained, which would represent a 
heat at which iron melts, or one sufficient to keep lava in a state of molten 
liquidity at the surface of the earth. ,? 
The distance of twenty-five miles between the source and 
phenomena of internal beat strikes us at first as being too 
great to be admitted as true. But this distance sinks into 
nothing when we reflect on the fact that twenty-six millions of 
miles separate the sun from the phenomena of the vegetable 
kingdom, known to be the results of it’s heat. 
We have reason to believe that it is this internal heat that 
produces earthquake action, volcanic action, metamorphic ac¬ 
tion, thermal waters, boiling springs, and the complicate phe¬ 
nomena of mineral strata, and mineral veins. If bv the aid 
of science Sir John Herschel could thirty-eight years ago, say 
that “ the sun’s rays are the ultimate source of almost every 
motion which takes place on the surface of the earth,” we may 
safely say to-day, that this central heat is the ultimate source 
of almost every motion which takes place, and has taken place- 
in the crust of the earth ; that it is to the mineral kingdom 
what the sun is to the vegetable kingdom, the ultimate source 
of physical forces and conditions. 
This brief explanation of the nature of the physical condi 
20—Ag. Tr. 
