302 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
Here the including rock shows no greater amount of metamorphism in the 
vicinity of the lime than elsewhere; while in neither lime nor including rock 
are there to be found any minerals, other than the ordinary ingredients of their 
general mass. And all this also holds with equal force in the circumstances of 
the lime stratum being of considerable extent, so long as it is untroubled—un- 
convoluted. 
But it is not so if the stratum be at one and the same time large in mass, 
and either itself highly contorted, or, in those cases in which it is not sufficiently 
exposed for this to be determined, if it be seen to be lying in the midst of 
highly contorted rocks. Then the calcareous mass no longer is amorphous in 
its substance, and organic in its structure; it presents itself as a granular 
limestone, often as a true marble; that is, it is calcite, and is crystalline in 
structure, and in all its inherent properties. Again, the including rock is, 
in the immediate vicinity, much more highly metamorphosed than it is through- 
out its general mass. While lastly, imbedded in the limestone, and to a 
smaller extent in the altered rock, but in both cases near their point of contact, 
there are found numerous minerals, a// of which are such as can be formed 
by the union of the constituents of the inclosed limestone with those of the 
inclosing gneiss. 
The assigning of the above local changes to the mere presence of limestone, 
in a rock which is undergoing ordinary metamorphic change, will not suffice as 
an explanation of what is found in the above case. 
Ordinary metamorphic change is, in our almost total ignorance of the sub- 
ject, usually assigned to a hydro-thermal action, which has taken place at great 
depths, z.e., under enormous pressure. Such a thermal change should affect a 
plicated, and a nonplicated included rock alike ; and should certainly affect a 
thin bed of lime more than a thick. As the result of any change thus passing 
from without inwards,—that is, from the gneiss to the limestone,—we should 
expect to find the thinner parts of the stratum of the latter wholly converted 
into large granular marble, and very fully pervaded with mineral species ; while 
the thicker parts of the lime should be much less altered in both respects: but 
this is the opposite of what obtains; and so any explanation which requires 
that the agent of change should act from without inwards does not suffice. 
The whole facts of the case seem to point to an action taking place from 
within outwards. So at least is it to be seen how there should be greater change 
where the stratum is thickest ;—the greater the mass, the greater must be the 
amount of action, if that action proceed from within. 
But what action, physical or chemical, can be conceived to take place within 
or emanate from a sedimented, amorphous, organic limestone, which shall credit 
it with being at one and the same time the agent of its own metamorphosis into 
its crystalline allomorph,—of augmenting the metamorphosis of a rock in its 
