198 GKOGNOSTICAL SKETCH OF THE 
ly to consist of one substance, namely, grey gneiss. This 
rock is of a very soft nature, and hence is easily penetrated 
by frost and running water. It is disposed into thin strata, 
which do not rise much above the horizontal position, and 
are inclined, in this place, towards the south or south-east. 
It would be useless to record any of the varieties of this 
gneiss, as they are but few in number, and depend only on 
the proportions and colour of the different ingredients. 
The most interesting circumstance attending these strata is 
the occurrence of granite veins. These are extremely nu- 
merous, and their courses are completely displayed on the 
sides of the gully. They seldom coincide with the strata 
of gneiss, but generally cut across their direction, at an 
angle variously inclined, rarely perpendicular. The gra^ 
nite veins vary in thickness from half an inch to two feet. 
These veins consist of a red or white, large, granular gra.. 
nite, similar in general to the granite just described, as oc-» 
curring in the mass of Phopachy hills, but differing as to 
the intensity of the colour and lustre, as well as in hardness. 
This latter property is often so great, that I have observed 
the granite veins hanging over a precipice, after the softer 
gneiss has been swept away. Their colour also points out 
their direction among the grey strata of gneiss. 
These veins afford a fine study to the geologist, exhibit- 
ing great variety of intersection, shifting, and branching ; 
and although the gneiss near to them is sometimes contort- 
ed, it also exhibits the same structure where no veins are 
visible. 
To these observations I have only to add, that the gneiss 
does not extend along the margin of Loch Ness above two 
miles. It then gives place to a small-grained granite, or 
granitic gneiss, which forms nearly the whole of the re- 
mainder of this chain up to Fort Augustus, and, conse- 
quently, the last substance we have to describe in this part 
pf our circuit. 
