3°4 
THE TERTIARY VOLCANOES 
BOOK VIII 
other, have forced their way between and partly across the bedding planes 
of the Carboniferous shales (Fig. 3 17). In this way the huge, unbroken 
mass, 250 feet thick, subdivides itself and disappears in a few hundred 
yards, though it continues a little further inland, and approaches the shore 
again half a mile to the south-west. Further evidence of the intrusive 
nature of this rock may be observed along the base of the precipice, where 
at least one sheet 70 feet thick diverges from the main mass and runs east- 
Fio. 317.— Section at Farragandoo Cliff, west end of Fair Head, showing the rapid splitting 
up and dying out of an Intrusive Sheet. 
a, Carboniferous sandstone ; b, Carboniferous shale ; c, intrusive sheet. 
wards between the Carboniferous shales (Fig. 315). At the contact with the 
eruptive rock the shales are everywhere much indurated. 
ii. SKYE 
All through the Inner Hebrides the base of the basalt-plateaux presents 
abundant examples of sills. The general parallelism of these intrusive sheets 
to the bedding of the Jurassic strata among which they lie has been above 
referred to as having given rise to the erroneous conclusion that in Skye and 
elsewhere the basalts are interstratified with Jurassic rocks, and are conse- 
quently of Jurassic age. It was Macculloch who first described and figured 
in detail the proofs of their intrusive nature. -His well-known sections in 
plate xvii. of the illustrations to his work on the Western Islands have been 
repeatedly copied, and have served as typical figures of intrusive igneous 
rocks. 
Nowhere in North-Western Europe can the phenomena of sills be studied 
so fully and with such exuberance and variety of detail as in the island of 
Skye and its surrounding islets. On the western coast the greater sub- 
sidence of the basaltic plateau has for the most part submerged the platform 
of intrusive sheets, though wherever the base of the bedded lavas is brought up 
