164 | Messrs. Hicks and Davies— 
was reached, being covered by Cambrian sandstone with the usual 
S.E. dip, whilst retaining in its own beds a strike at right angles 
to these, with high contorted dips. 
As a probable explanation of the frequent occurrence of igneous 
rocks along this line from N.E. to §8.W. may be mentioned, the de- 
pression which affected this line during. and probably even before 
the earlier Paleozoic epochs. That the Paleozoic contractions were 
accompanied. with elevations and depressions along lines more or less 
from N.E. to 8.W. is generally granted for at least the British 
areas. Such a line extending from here through the length of 
Ross and Sutherland is indicated by the presence now of the newer 
deposits in the hollows so formed, and the crush seems to have been 
depressed to a greater depth and have suffered more from the 
pressure here than at any other, except in the parallel line along 
the channel separating the Hebrides from the main land. 
This depression, as usual, was accompanied with many fractures 
of the crust, generally parallel with it, and these offered numerous 
channels and lines of weak resistance for igneous intrusions. ‘These 
faults from N.E. to §.W., combined with those at right angles to 
them, comprise the main systems recognizable in these areas, and 
have contributed mainly in producing the physical features. Most 
of the Lochs and Lakes run in a direction from N.W. to S.E., or in 
lines of fractures along the strike of the old rocks. The wider 
and more regular depressions are, on the other hand, in lines more 
or less across the strike of the Pre-Cambrian rocks. Various local 
shiftings have taken place here and there also, but the general 
result is the same throughout, and is usually easily recognizable. 
The more visible effect of all this upon the newer rocks has been 
to tilt them up and to crush them; but in addition, on careful ex- 
amination, a further change is recognizable. The rocks in proximity 
to these intrusions are more or less altered (or metamorphosed) 
from the combined influence of contact with igneous rocks and the 
evolution at the time of heated vapours. It has been generally sup- 
posed that the overlying deposits have been less altered along this line 
than the still newer rocks further east, and at a distance from these 
intrusions, and various theories have been propounded to explain 
this seeming anomaly. Some supposing that at these places there 
are invisible igneous foci; others that some process of selective 
metamorphism has taken place. Curiously the advocates of these 
views seem quite to have forgotten that wherever great igneous 
masses are seen, no such changes are observed to have taken place 
in the neighbouring rocks for any considerable distance from the 
mass ; selective metamorphism also should not affect all the rocks in 
an extensive area alike, and be entirely wanting in rocks presu- 
mably of like nature, made up of identically the same materials, 
derived from exactly similar sources, in neighbouring areas, which 
to all appearances have been subjected to the same influences. 
The evidence, as far as I am able to read it, goes to show that the 
most highly altered of the newer deposits are found along this line 
of depression usually in contact with intrusive rocks, or near fractures 
