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mineral consisting of iron and sulphur, from the decomposi- 
tion of which, by the hand of nature, aided by the presence 
of moisture and atmospheric air, the carbonic acid and nitro- 
gen of the water are indirectly derived. The carbonic acid 
is most likely evolved by a second decomposition of a slaty 
calcareous marl, found associated with the pyrites, and the 
chemical action which ensues may be thus explained : the 
sulphur of the pyrites will, by the absorption of the oxygen 
of the atmospheric air contained in the water, (for all at- 
mospheric waters are imbued with air,) be converted into 
sulphuric acid, a part of which will seize the base of the 
marl (lime) by superior affinity, to the disengagement of the 
carbonic acid with which it was previously combined. 
The origin of the nitrogen, the other gaseous fluid, must 
be ascribed to its dissociation from the oxygen of the atmos- 
pheric air contained in the spring, prior to its reaching the 
pyrites. Kitrogen is of rare occurrence in cold springs, 
whilst atmospheric air is nearly universal. The oxygen, there- 
fore, necessary to the sulphur becoming sulphuric acid must 
arise from this source disengaging the nitrogen ; for, unlike 
most waters, this contains no atmospheric air, and must have 
lost it in the way supposed. In thermal springs nitrogen is 
very abundant, and has by some been regarded as sufficient 
evidence that they owe their elevated temperature to che- 
mical action ; but when it is considered that the temperature 
of these waters, when issuing at points of extreme displace- 
ment, is highest, and that they are by no means confined to 
volcanic regions, it must be inferred that their heat is de- 
rived from the depth of the channels in which they flow; and 
the atmospheric air which accompanies them being deprived 
of its oxygen, accounts for the pressure of the nitrogen, 
which returns to the surface. The bluish slate marl already 
noticed supplies both the lime and magnesia. The silica is 
taken up by solution from the sandstones, and the alumina 
from the clay. 
