86 HISTORY OF THE EARTH. 
and used in the province of Artois in France, (the ancient Arte- 
sium) these have received the name of Artesian wells. 
The water yielding stratum of sand has sometimes to be sought 
at great depths, and in the course of the operations employed for 
reaching it, evidence is obtained of the same general kind with 
that afforded by mines, that the temperature increases as we de- 
scend. Artesian wells are sometimes but more rarely obtained 
among the secondary strata. 
3. The hot springs which rise out of the earth in many parts of 
the globe, but appear to be more numerous near the line of junction 
of the primitive rocks with the more recent strata, indicate that 
the internal sources of heat are not confined to the neighborhood 
of volcanic mountains or the mines of western Europe. Such 
as are particularly remarkable for the quantity, or the tempera- 
ture of their waters, have attracted attention, but it is only recent- 
ly that their bearing upon the science of Geology has been seen, 
and that they have become particular objects of interest and ob- 
servation. Their peculiarities were formerly attributed to chemi- 
cal changes of limited extent and influence, proceeding in the 
strata from which they rise. But the volume of the water given 
out by them in many instances, its temperature, and purity, in- 
dicate rather a temperature elevated considerably above that of the 
surface, extending through the whole mass of rocky strata in 
which they have their origin. It is evident that this heat may be 
derived by slow communication from an internal nucleus. If 
hot springs shall be regarded as furnishing satisfactory indica- 
tions of the existence of an interior source of heat, a very great 
amount of evidence may be drawn from this quarter, since there 
are few countries in which they have not already been discovered, 
and it is probable if not certain, that a diligent search over the 
whole earth would lead to the detection of many that are hither- 
to unknown. The gas that issues along with the water of hot 
springs is generally nitrogen. The warm springs ofBuncomb 
have a temperature of about 104 of Fahrenheit. 
4. Some of the phenomena of earthquakes accord with the 
idea that the crust of the earth is a mass of rock resting upon the 
surface of a subjacent liquid. Such are, the vibratory motion in- 
to which it is thrown, and the heaving of the ground resembling 
the boiling of a fluid or the billows of a swelling sea that have 
been observed in a number of instances. A person standing 
upon a float of logs or a large piece of loose ice, will be agitated 
somewhat in the same way as during an earthquake. This argu- 
ment is not however of any great weight. A heav)' carriage driven 
rapidly over a pavement will shake the edifices in the neigh- 
borhood. A considerable commotion in its interior, by whatever 
eause produced, would perhaps be adequate to the production of 
all the phenomena of earthquakes, even supposing the earth to be 
solid throughout its whole extent. 
5. Volcanoes will not as obstinately defy our attempts to as- 
