48 Proceedings of Royal Society of Edinburgh. [sess. 
more recent gneisses, which constitute the hulk of the Highlands 
from Loch Eriboll to the Firth of Clyde, represent the same strata, 
which lie between the chocolate-red Cambrian sandstones of the west 
coast, and the Old Eed Sandstones on the eastern side, of that county. 
The rediscovery by Peach of the fossil remains so long before detected 
and indicated, by Macculloch, enabled Murchison to present this 
generalisation as firmly resting both on stratigraphical and on 
palaeontological evidence. I have never seen the least reason to 
suppose that the late marvellous discoveries of the Geological Survey 
in Sutherland cast the least doubt on Murchison’s general conclusion. 
Those discoveries, indeed, are of immense interest, and teach us 
many lessons on the dynamics of geology — lessons, I think, which 
were greatly needed. But it does seem to me that the hearing of 
these discoveries on the conclusions of Murchison is almost nil. 
They prove indeed that, in a middle region between the extreme 
west and the extreme east, there has been local disturbance of an 
extraordinary kind, and that in that region the present order of super- 
position cannot he taken as determining the geological age of the 
rocks, owing to reversing and overlapping faults — “ thrust-planes,” 
and other phenomena of earth movements so peculiar that they seem 
to have already called forth a completely new nomenclature as re- 
quisite to describe them. It is a curious fact that Macculloch, with 
a penetrating and almost prophetic eye, seems to have suspected 
this area of country to he one of unusual disturbance. He speaks of 
“ two distinct deposits of gneiss, of which one is placed in a reverse 
position to the other.” He speaks of “ essential disturbances among 
the primary rocks,” due to “ one or more revolutions,” separated by 
“ long intervals of time.” He speaks of “ the science of geology 
being not yet sufficiently advanced ” to afford any complete explana- 
tion of the peculiar phenomena of that region.* All this sounds 
like a dim prevision of the wonderful inversions of the natural order 
of the rocks in that part of Sutherland, due to most “revolution- 
ary” movements of subterranean force, which have only just been 
discovered and laboriously traced by the Geological Survey. Nothing 
but such a mapping and tracing of every bed in the greatest detail 
could have unravelled such inversions, conversions, distortions, and 
horizontal displacements. Murchison did not know of these, and he 
* Macculloch’s Western Islands , vol. ii. pp. 202-3. 
