Contribution to Vertebrate Fauna of West Ross-shire. 383 
fauna, while in other less direct ways peculiarities of rock- 
structure, soil, and glacial phenomena may be shown to be 
important factors in determining the presence and distribu- 
tion of certain species. 
A general sketch of the geology of West Ross, with special 
reference to the points more directly affecting its faunal 
character, may then, be not altogether out of place. 
A glance at the most recent geological map of Scotland 
shows that the rocks of West Ross arrange themselves in 
three well-marked zones of varying breadth, running parallel 
to the western coast in a N.N.E. to 8.S.W. direction. 
These are (beginning in the west),— 
1. The Pre-Cambrian Zone—including the Archean or 
Lewisian Gneiss and the Torridon Sandstone. 
. The Cambrian Zone. 
3. The Eastern Schist Zone. 
bo 
1. The Pre-Cambrian Zone.—The Lewisian Gneiss occupies 
a large area in Gairloch and Dundonnell, extending from 
Talladale and Shieldaig south of Loch Maree to the coast 
on the east side of Gruinard Bay. Isolated patches of 
gneiss also occur on both sides of Loch Torridon at the 
narrows, and extend along the southern shore of the outer 
loch as far as Arrin-na-chruineach. 
This gneiss, generally conceded to be the most ancient 
rock in the British Isles, is of an exceedingly tough and 
uncompromising character, yielding little to the forces of 
atmospheric denudation, and hence peculiarly well fitted to 
preserve the traces of glacial action, traces nowhere so dis- 
tinctly visible as in the seaward parts of West Sutherland 
and West Ross. The country where the Lewisian Gneiss 
prevails is consequently for the most part bare and rocky, 
with ice-smoothed hummocky ridges succeeding one another 
in dreary monotony. Generally barren of soil and herbage, 
there is little in these regions to attract bird-life. The 
innumerable small lochans, often partly covered with weeds 
and water-lilies, that fill the ice-carved rocky hollows, afford, 
however, breeding ground for a few pairs of Lesser Grebes 
and Red and Black-throated Divers; while the islets in the 
