304 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
of active energy the difference in the amount of the specific heats of carbonate 
of lime in its two states,—the excess which is special to it in the colloidal. 
This expressed heat left only a residue, so to speak, sufficient for granular 
limestone ; while it became the active agent in stimulating the chemical affini- 
ties existing between lime and the silica, alumina, and alkalies of the gneissose 
matrix. It thus led directly to the formation of minerals, while it at the same 
time expedited or perfected a more thorough metamorphosis, ¢.¢., the assump- 
tion of a more perfectly developed crystalline structure, in the previously only 
partially metamorphosed rock. 
The assumption of a definite crystalline structure,—a character or property 
directly attached to a definite chemical composition,—must of necessity extrude 
from the resultant calcite the phosphate of lime and fluoride of calcium which 
limestones contain uniformly distributed throughout their mass. Apatite and 
Fluorspar are accordingly among the crystallised minerals found imbedded in 
the saccharoid “ primary ” limestones. 
Whether the extruded heat can actually fuse the residual calcite may pos- 
sibly yet be ascertained by direct experiment ; but it would seem to be almost 
a necessary deduction, that no mineral could be formed by such an action pos- 
sessed of or requiring a specific heat greater than that of the original source of 
the expressed heat. 
It must be borne in mind that chemical elements do not alone go to the 
formation of any substance ;—a due amount of certain physical agencies is the 
special portion of each, lodging as it were in their pores as resting places. Of 
the chemical ingredients, one alone may suffice ; of the physical, among which, © 
heat, phosphorescence, and magnetism may be said to be those most germain 
to minerals, heat is the only one which is never absent. Chemical affinity 
then can only predispose to the union of the constituents which go to form the 
substance ; for something more is requisite before the formation can be accom- 
plished,—hefore the substance can, so to say, assume an independent existence, 
—namely, the supply of the heat special to it,—to the perfect putting together 
of the whole as a mineral species. 
It has, however, to be admitted that we are unable positively to affirm that 
the expressed heat may not be so concentrated in the spots where the chemical 
action is operating as to afford any specific heat required. 
Two arguments against such a view may, however, be adduced. 
The first—That the heat extricated throughout the general mass would not 
readily be localised, or carried specially to any point in so badly conducting a 
substance as granular limestone or marble ; more probably would it accumulate 
within the limestone itself, even to the point of its fusion ;—and indeed the 
occurrence of porphyritically disposed crystals of quartz with rounded angles 
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