10 A. Geikie—Crystalline Rocks of the Scottish Highlands. 
IV. Calcareous rocks. 
os a 1. Limestone. 
f[esresjesves fooese]--2+-]oee ° . 
: ic or arenaceous limestone. 
2. Quartzytic or arenace 
3. Argillaceous limestone: like 2, with a line in place of the 
dots. 
The above are examples of the proposed system of symbols. 
For rocks not included above, other symbols in accordance with 
the system may readily be devised, where the science requires 
them. 
Art. IV.—The Crystalline Rocks of the Scottish Highlands; by 
ARCHIBALD GEIKIE. 
EVER since the discovery of Silurian fossils in the rocks of 
Northwest Sutherland, it has been recognized that in that 
region lies the key to the structure of the Scottish Highlands. 
Accordingly, when in the progress of the Geological Survey, 
the mapping of the Highlands had to be undertaken, I deter- 
termined that a detailed survey of the Sutherland ground on 
the scale of six inches to the mile should be made as a basis» 
for the work. In the summer of last year a surveying party 
under the charge of Mr. B. N. Peach was stationed there, with 
instructions to begin by mapping the Durness Basin. This 
duty was satisfactorily accomplished before the end of the 
season. The Silurian series of Durness was ascertained to be 
about 2,000 feet thick, and to consist of numerous successive 
zones, which were traced on the six-inch maps and discrimin- 
ated in such a way as to be recognizable should they be found to 
