3§4 
THE TERTIARY VOLCANOES 
BOOK VIII 
its margin, we may perhaps reasonably infer that these outliers of limestone 
are remnants of a once continuous limestone sheet that overlay the eruptive 
rock, and hence that, with due allowance for considerable denudation, the 
present surface of the boss represents approximately the upper limit to 
which the granophyre ascended through the limestone. The actual facts are 
shown in Tig. 347. 
All round the margin of this boss, the limestone has been converted for 
a variable distance of a few feet or many yards into a granular crystalline 
marble. The lighter portions of the limestone have become snowy white ; 
but some of the darker carbonaceous beds retain their dark tint. The 
nodules of chert, abundant in many of the limestones, project from the 
weathered faces of the marble. The dolomitic portions of the series have 
likewise undergone alteration into a thoroughly crystalline -granular or 
saccharoid rock. The most thorough metamorphism is exhibited by portions 
of the limestone which are completely surrounded by and rest upon the 
granite. The largest of these overlying patches was many years ago 
quarried for white marble above the old Manse of Kilchrist. I have shown 
by lithological, stratigraphieal and palaeontological evidence that this lime- 
stone, instead of belonging to the Lias, as was formerly believed, forms a 
part of the Cambrian or possibly the very lowest Silurian series, being a 
continuation of the fossiliferous limestone of western Sutherland and Ross- 
shire. 1 Mr. Clough and Mr. Harker, in the progress of the Geological 
Survey in Skye, have ascertained that the distinctive characters of the three 
groups of strata into which the limestone can be divided may be recognized 
even through the midst of the metamorphism. 2 
The generally vertical line of separation between the rock of Eeinn an 
Dubhaich and the contiguous limestone lias been taken advantage of for the 
segregation of mineral veins. On the southern boundary at Camas Malag, a 
greenish flinty layer, from less than an inch to two or three inches in width, 
consisting of a flnely-granular aggregate of some nearly colourless mineral, 
which polarizes brilliantly, coats the wall of the granophyre, and also both 
sides of the vein which proceeds from that rock into the limestone. But the 
most abundant and interesting deposits are metalliferous. Fragments of a 
kind of “ gossan ” may be noticed all along the boundary-line of the boss, 
and among these are pieces of magnetic iron-ore and sulphides of iron and 
copper. The magnetite may be seen in place immediately to the south of 
Kilbride. A mass of this ore several feet in diameter sends strings and dis- 
seminated particles through the surrounding granophyre, and is partially 
coated along its joints with green carbonate of copper. 
From the Skye area important evidence is obtainable in regard to the 
relation of the acid eruptions to (1) earlier eruptive vents filled with agglo- 
merate ; (2) the bedded basalts of the plateaux; (3) the bosses, sills and 
dykes of gabbro and dolerite ; and (4) the great system of basic dykes. 
(1) Relation of the Granophyre to older Eruptive Vents . — The grano- 
1 Quart. Journ. Geol. Soc. vol. xliv. (1888) p. 62. 
- Annual Report of Director-General of the Geological Survey for 1895. 
