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heat. It is well known that igneous matter, in the form 
of toadstone, has been poured out between the layers of 
limestone to a considerable extent. This heated mass 
would tend to evaporate all liquids contained in fissures 
within its influence, and, the process being a very slow one, 
the solids would crystallize in regular forms. It is a ques- 
tion whether these crystalline deposits of metallic ores, &c, 
were formed prior to the effusion of igneous matter between 
the limestone, or at the time it lay dormant beneath the 
whole mass. I think the continuation of the same lode above 
and below the toadstone is a sufficient proof that the for- 
mation occurred during the latter period, for had the fissure 
been open at the time of this igneous flood, it must un- 
doubtedly have been filled ; still the effect of this heat 
would be felt at the time the igneous mass lifted up the 
ocean bed to its present position, and it would not even be 
necessary to have recourse to its second or third effusion 
to account for these results. 
Having attempted to explain the production of the sul- 
phurets, I will now endeavour to give a brief outline of 
the formation of fluor spar, calcareous spar, &c. With 
regard to the first, I may remark that it consists of a simple 
elementary substance, — fluorine, and the metallic base of lime. 
I believe this substance is seldom or never found except in 
the neighbourhood of igneous rocks ; hence we may premise 
that fluorine in some form or other must have been given off 
from the ignited mass itself. But it is well known that 
fluorine could not be given off in a free state if silica was 
present, because it possesses a very powerful affinity for its 
base, — silicon, and forms with it a volatile body, — the fluoride 
of silicon. Hence, if given off from igneous rocks at all, 
it must be in the form of this gas. Now, on bringing this 
substance in contact with water it would be decomposed, 
giving rise to hydrofluo-silicic acid, and free gelatinous silica, 
