CHAP. XLII 
THE BASIC SILLS OF SKYE 
3*3 
which has insinuated itself among shales, shell-limestones, and shaly sand- 
stones, full of Ostrea hebridica, Cyrena aurata, etc., and belonging to the 
Loch Staffin group of the Great Oolite Series. The shore-cliff below the 
waterfall affords the section given in Mg. 322, illustrating the manner in 
which a thick intrusive sheet may sometimes give off' thin veins from its 
mass. The rock attains on the Eist promontory a thickness of probably at 
least 100 feet, where it is thickest and undivided. But the two main 
sheets, or branches of one great sheet, on this peninsula have probably a 
united depth of more than 300 feet. Landwards the rock splits up and 
encloses cakes of the Jurassic strata. It possesses the usual prismatic struc- 
ture and doleritic composition. In Moonen Bay, as shown in Eig. 322, it 
presents a banded structure, marked especially by an alternation of lines of 
amygdales and layers of more compact and solid dolerite, with occasional 
enclosed cakes of baked shale or sandstone. Its upper surface is somewhat 
uneven, and from it are given off narrow, wavy, ribbon-like veins ( d ), from 
less than an inch to three inches or more in width, which keep in a general 
Fig. 322.— Upper part of Sill, Moonen Bay, Waternish, Skye, showing the divergence of veins. 
a, false-bedded shaly sandstone ; b, shell-limestone; c, dolerite sill ; d, veins proceeding from the sill. 
Length of section about live yards. 
sense parallel to the top of the sill, hut at a distance of a few inches or feet 
from it. The sill becomes as usual fine-grained towards the contact, the 
shales and sandstones being indurated and the limestone mannorized. 
The next uprise of the base of the basalt-plateau on the west side of 
Skye lies about 25 miles to the south-east, where it emerges from the sea in 
the Sound of Soa (Eig. 323). A vast volcanic pile has there been heaped 
up on the Torridon sandstone, the whole of the thick J urassic series, which 
is found in force only three miles distant in Strathaird, having been removed 
by denudation from this area before the beginning ol the Tertiary volcanic 
period. The plateau-basalts rests ou the upturned edges of the Torridonian 
sandstones and shales, and are accompanied as usual by their underlying net- 
work of intrusive rocks. It is hardly possible to exaggerate the wild contusion 
of sills, dykes and veins which have been injected among the rocks, at and on 
both sides of the unconf or inability. Endless sheets of basalt and dolerite 
have forced their way between the bedded basalts and the sandstones, while 
across the whole rise vast numbers of dykes and veins. Narrow, black, 
