492 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
beds to the west of Portsoy, the first from gabbro, the larger apparently from 
euphotide ; the beds to the east, from a rock chiefly augitic. 
The peculiar structure of the serpentine of the hill of Towanrieff would 
lead to the conclusion that gneiss was the original; but the nearest rock is a 
laminated diorite, composed of labradorite and black mica. 
The Green Hill of Strathdon, from diorite rich in augite ; that of Culbleen, 
Coyle, and some of the Shetlands, is obscure. A bed in the Farrid Head, 
Sutherland, unquestionably from gneissic schists. 
Though these conclusions are chiefly the result of geognostic observations of 
the district, there are many localities where the transition may be traced through 
a gradual change in the minerals composing the rock. Such comparatively 
molecular transformation may be well studied on the north shore of Swinaness, 
in Unst, in several places in the neighbourhood of Portsoy,* on the north side 
of the hill of Towanrieff, and on the northern slopes of the Green Hill of Strath- 
don. At the last-mentioned locality there may be obtained unaltered, or ap- 
parently unaltered, diorite ;—the same with the hornblende duller in lustre and 
softer than normal, and the felspar dull, semi-opaque, and of a greasy lustre ;— 
and lastly, almost perfectly formed serpentine, in which, however, the granular 
structure of the altered rock is plainly visible. These three occur within the 
space of a few feet of each other. It is not, however, easy to select for analysis, 
from rocks—the several crypto-crystalline ingredients of which give way to 
the transmuting agent at different periods of time—-specimens at once typical 
and sufficiently pure. I have met with more success in this direction in 
working among the serpentinous marbles—those which contain imbedded 
granules or patches of serpentine—than I have among the larger masses of 
the serpentine rock itself. 
One fact I would direct attention to, seeing that it has perhaps not been 
clearly enough considered, namely, that great beds of serpentine must have 
been formed by the metamorphism of pre-existent rocks as a whole; that 
although the change took place step by step, one ingredient giving way before 
another, still, ultimately, all participated more or less thoroughly in the change. 
The molecular or crypto-crystalline transformation had thus,as its result a litho- 
logical transmutation. To be more precise, where a great bed of diallage rock 
has been converted into serpentine, the felspar as well as the augite has gone to 
form the latter. This magnesian metamorphosis of labradorite does not seem 
to have been sufficiently recognised ; but though the general rule is that the 
augitic mineral is the first which suffers alteration, there are localities in which 
the felspar would seem to have been first affected, It is true, that in many 
cases the felspar may not have been converted into true serpentine, but merely 
into an impure kaolin, which, disseminated throughout a serpentinous. basis, 
* Specially at the Bay of Durn, north of the Battery, and. the first bed to the west thereof: 

