PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. (4 
cutting west of Banchory, this gneiss is becoming granitic through a regular 
increase in the number and in the volume of these granitic bands. Here also 
there is a marked change in the nature of the bands themselves ; they no longer 
exhibit the laminated structure, but are throughout their whole extent true 
granite of a uniform fine grain; and although the hammer can still discover no 
line of separation, yet a finger’s breadth will here cover the space through 
which the structures pass from one to the other.* 
In following the line of railway to its next cutting, nearer to the Hill of 
Fare, the granitic bands will be seen progressively augumenting in width, and 
the gneissose bands dwindling to evanescence. 
For such as I have now described, and also for the more rectilinear modifica- 
tion thereof which occurs in hornblendic gneiss, I would propose the term 
bands of metamorphic segregation. 
The second mode of change is well seen in the quarries at Tillyfourie. 
The gneiss, which here presents bold features,—being highly contorted, 
broadly banded, the bands showing an abrupt contrast in their coloration,— 
passes into granite with an abruptness which is quite startling. 
There is not a trace of interstitial skin or intermediate mineral body ; most 
assuredly there has been no intrusion of the granite here,—the one rock ceases 
to be, and the other commences along no line which can be seen or felt ; there 
is no portion of space in which the one can be said to be in contact with the 
other ; the continuity is everywhere unbroken, the material continuous, the eye 
alone appreciating a marked change of colour and of structure, for the openings 
between the foliz of the gneiss suddenly cease to exist, but this they do not 
along a rectilinear but a wavering course. A hammer blow rends the rock in 
any direction, the line of fracture crossing the zone of changed structure at all 
angles, and the straight course of the fracture being uninfluenced in the so doing. 
The only modification of this structure is, that occasionally the dark mica of the 
granite has its plates disposed in arrangement somewhat parallel to the course 
of the transition, within the space of an inch or two from the unchanged rock. 
The third mode of change is seen in the several quarries of the Stony Hill 
of Nigg; here a fine-grained, plicated, and darkly-striped gneiss may be 
traced, with gradually fading layers, into a uniformly granular, dark grey 
granite. In many of the Aberdeenshire quarries, moreover, semiangular frag- 
ments, large and small, of the darker and more micaceous layers of the 
gneiss, are found imbedded, rounded in their outlines into kidney-form 
“neres”), and darkening the granite in their immediate vicinity by a quantity 
of the black-mica (Haughtonite) which these “neres” contain. It would 
* While confounding these bands with “contemporaneous veins,” JAMESON saw clearly their marked 
features. He writes—‘These veins do not present the slaty structure which is one of the discriminating 
characters of gneiss when it occurs in strata; hence contemporaneous veins, filled with common granular, or 
what may be called granitic gneiss, have been confounded with true granite.” Thereby meaning common or 
eruptive granite. 
