PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 541 
original thickness of the stratum of transformed rock ; also thicker or thinner 
according to whether that rock was augitic or hornblendic ; for the former can 
supply considerably more lime than the latter. This calcareous belt must lie 
beneath the parent rock, sealed against any great amount of further change, 
unless or until upheaval or denudation expose it to meteoric influences. Then 
water, flowing either downward or upward, may—-nay, in time must—sweep it 
away in solution, leaving lime-sink, or collapsed-void to evidence its former 
existence. But if the limestones, so frequently associated with serpentines, 
are thus to be assigned to the decomposition of the rock which yielded these 
serpentines, we have a crucial test of the soundness of the theory of the change, 
in the inquiry as to whether wnchanged gabbro, or other such rocks occur in 
} contact with lime. 
That it never does, I will not say; but, in glancing at a sketch geological 
map which I have constructed of the district where these rocks occur, I find, 
as regards the great belt of diorite and diallagic rock which sweeps up central 
Scotland, that where either the limestone appears in contact with it, or a 
“wash-out ” discloses its former existence, there the rock is serpentine ; where 
it appears as unaltered rock there is no lime. 
I find, moreover, that wherever the association can be observed, the lime 
invariably is beneath the serpentine. So it is with the loch of Cliff lime and 
the serpentine of Unst; both of the lime and serpentine beds at Polmally ; 
both of the lime and serpentine beds at Portsoy ; at Limehillock ; Tombreck ; 
the Green Hill of Strathdon; and Beauty Hill; and in enumerating these I 
have named all the most important masses in the country. 
The evidence of our transmuted minerals thus goes a long way to prove 
serpentine to be a metamorphic, and not an igneous, rock, whether the 
chemical process proposed in explanation of the modus operandi of the change 
be or be not considered satisfactory. 
But there are occurrences of serpentinous matter differently circumstanced, 
where the above explanation can by no means suffice. 
By the dissolving out of the lime from a stratum either of gabbro or of 
labradoric diorite, we would obtain a great mass of limestone, it is true; but 
that mass, relatively to the simultaneously formed serpentine, should be com- 
paratively small. 
The hornblende of Portsoy would yield equal to about 34 per cent. of 
carbonate of lime—its labradorite would yield about 20 per cent; and, as in 
the diorite rock, the hornblende is to the labradorite in about the proportion 
of 2 to 1, this rock as a whole would yield about 29 per cent. of its original 
| bulk; of which, however, there remains still 84 per cent., for 13 of the 29 
consist of direct addition of carbonic acid. Here, then, we have a rock 
VOL. XXVIII. PART IL. < & 
