PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 519 
ean fail in good light to see the gneissose structure, still apparent when 
viewed at a distance of a dozen of feet or so; and no one who follows up the 
regular bedding of the diorite, diallage, and limestones, with associated thin rifts 
of serpentine, quartzite, and gneiss, throughout the forty or fifty miles which they 
extend, with flexures ever accommodating themselves to those of the inclosing 
rock, can but regard them as regularly bedded and non-intrusive. 
That it may not primarily have been an interbedded igneous rock, it might 
be rash absolutely to deny ; but the convoluted schistose structure occasionally 
evident in the rock, on the one hand, and its apparent transitions into laminated 
sedimentary rocks on the other, go far to preclude such a view. It must be 
admitted, however, that one belt of rock on the west side of the Bay of Durn 
has very much the appearance of an igneous origin. 
There is another relationship of this rock, however, or of a very similar one, 
which, having been somewhat forcibly insisted on, calls for some notice. 
Maccuttocw in his “Classification of Rocks” has, under binary granites, 
_ the following :— 
D. FELSPAR AND HORNBLENDE. 
a. Large-grained, or the hornblende crystallised. 
b. An uniform granular mixture ; the respective ingredients varying materially in their 
| sizes and proportions, so as to produce a great variety of aspect. 
ce. Intimately mixed so as to be nearly undistinguishable. 
| Var. 6 often resembles the greenstones of the trap family; and is in fact only distinguished 
by its geological connection with granite. Var. c is often similarly undistinguishable from 
| basalt; occasionally from the non-fissile hornblende schists; but, like variety 6, it is connected 
with, and passes into, granite of the common character. 
These varieties occur in Aberdeenshire, where they are connected with the most ordinary 
granite, subjacent to gneiss, both by transition and alteration, in a manner so distinct as to 
leave no doubt respecting their true place in a geological classification like the present. 
In Nicot’s “ Guide to the Geology of Scotland,” page 185, we read :— 
In Bennachie the granite is a reddish-brown binary compound of quartz and felspar, both 
in regular crystals, whilst on the northern face it approaches to greenstone or diorite. Some 
rare varieties also occur between Old Rayne and Meldrum, the common granite passing by 
| imperceptible transitions to a dark dioritic greenstone, and this to a uniform mixture not dis- 
tinguishable from basalt. But the identity does not cease even here, since in many places it 
passes in the same uninterrupted manner into a soft claystone, with a schistose tendency on 
exposure, in no respect differing from those of the trap islands of the western coast. In these 
varieties felspar and hornblende in various proportions compose the entire rock. The former 
mineral is sometimes white, inclosing hornblende crystals, when the rock has a very beautiful 
appearance. In the coarser mixtures the felspar is commonly white, but in the finer it becomes 
greenish; whilst the basalts seem mere hornblende invariably black. In a word, quartz, felspar, 
mica, and hornblende may be found in almost every conceivable variety of composition and 
