COxMMUNICATIONS 
TO THE 
MONTHLY MEETINGS, 
1860 . 
April 3 .— W. Procter, Esq., read a paper “On the mineralogy and 
formation of Fluor.” Fie commenced by a statement of the condi¬ 
tions necessary for the crystallisation of solids, and the reasons which 
had induced mineralogists to refer the formation of a very large class 
of natural crystals to the action of heat, but he thought that it might 
fairly be questioned whether this explanation, as a general one, does not 
admit of doubt, he illustrated some of the difficulties to be overcome 
in the case of Fluor, and endeavoured to show, from certain circum¬ 
stances connected with the mineralogy of that substance, that it had 
probably not been formed by igneous agency. The circumstances 
particularly discussed and insisted upon were the fact that it is often 
found associated with matter apparently organic; that Fluor is of 
very frequent occurrence in solution in various waters, and to such 
an amount (notwithstanding its small degree of solubility) that large 
quantities could be deposited, under certain circumstances, in a series 
of years. Another important source of information is derived from a 
consideration of the pseudomorphs of Fluor. Numerous examples 
of this class of minerals were adduced to show that their formation was 
irreconcileable with the supposition of igneous agency. The occurrence 
of Fluor in Lava or intimately blended with such minerals as Horn¬ 
blende is no proof of its igneous formation ; for as the Fluor crystals 
are small and found only in the older erupted masses, their formation 
is probably a product of the slow and continued action of percolating 
water on the Fluoritic minerals existing in those masses. It was then 
attempted to be shown that the two igneous theories,—first, that Fluor 
in a state of fusion was protruded from the interior of the earth, into 
fissures, and then collected and crystallised,—and, secondly, that Fluor 
was produced by the decomposition of carbonate of lime by the 
vapour of hydrofluoric acid, were untenable. It was contended that 
the assumption of aqueous agency leads to a sufficient and satisfactory 
explanation of the formation of Fluor, and that the balance of argument 
