PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 67 
Insoluble silica, 4:819 per cent. ; loses 1-961 per cent. of water in the 
bath. 
From Hornblendic Geiss. 
3. At the grandly picturesque headland of Cape Wrath,—or more correctly 
Rath,—the hornblendic gneiss of the west coast differs in its features very con- 
siderably from those which it possesses elsewhere, and which may be said to 
be almost unvarying. The dip here is low, and to the east. or east-south-east. 
It is highly corrugated and folded, and it is rent and shifted and reagglutinated 
by an anastimosing and mutually intersecting series of granitic veins. Its own 
granitic belts, instead of assuming as elsewhere much of the character of a set 
of parallel dykes, with abrupt and sharply-marked surfaces, blend by insensible 
gradation into the ordinary material of the rock, which is here even somewhat 
of the nature of granite itself. 
It is this greater consistency of the rock as a whole, this more intimate 
interpenetration and consequent firmer cohesion of its parts, coupled with the 
altogether unique manner in which its every layer is bound together by granitic 
cords of unusual toughness—interlaced in such a manner as to defy unravelling 
—that has enabled it to form so fitting a termination to a kingdom,—so 
enduring a rampart against even Atlantic billows. 
Such are the features of the rock for about a mile to east and south of the 
lighthouse. Another feature has, however, to be noticed ; it is, within the space 
so included, much less characterised by the presence of particles of hornblende 
than is usual, being of a pinkish instead of a green cast of colour. This local 
deficiency of hornblende is, however, more than compensated for at a point 
about one and a half miles south of the lighthouse, where the strata have 
gradually increased their dip, and assumed a line of outcrop which is that 
normal to the rock in the south. Here the beds suddenly become almost alter- 
natingly hornblendic and felspathic ; and as the intermediate felspathic bands 
have frequently yielded to the weather, those which are hornblendic stand 
erect in repeated sequence, simulating dykes of a dark igneous rock. 
Just about the same spot also, in cove-like recesses of the older rock, the 
horizontal strata of that many-coloured conglomerate which has been assigned to 
the Cambrian epoch, make their appearance in outlying portions of very circum- 
scribed dimensions. 
In the second (in progressing southward) of these coves of the Cambrian 
Sea,—one which is now sentinelled on the north by a grand development of 
the black bands of the older rock, and on the south by an equally grand illustra- 
tion of intrusively anastomosing granite,—my companion, Professor GEIKIE, and 
I hit upon an interesting mineral locality. 
VOL. XXIX. PART I. S 
