497 
of Edinburgh , Session 1868-69. 
and Bute, and stretching, as I have now ascertained, across the 
island to the coast of Haddington and Berwick. Between these 
lower sandstones and the base of the Carboniferous limestone comes 
a group of strata possessing much interest from the variations which 
it exhibits in thickness and in the nature of its component strata. 
In some districts it is altogether absent, and then the limestones 
and the red sandstones come together. But again, at no great dis- 
tance, it reappears, and soon acquires a considerable thickness. In 
the western part of the country, it consists of grey and white sand- 
stones, pale grey, green, or mottled marls and shales, with bands of 
cement stone, sometimes with dark shale and ironstone. The 
Ballagan beds of the Cn-mpsie Hills belong to this group. In the 
eastern half of the country, throughout the Lothians, it is made up 
of thick white sandstones, black shales, ironstones, some beds of 
limestone, and even of coal, its most important components being 
those bituminous shales from which oil is now so extensively 
obtained. In the east of Fife it contains a great many bands of 
limestone, having the fossils and general aspect of true carbonifer- 
ous limestone beds, while in Berwickshire it reassumes the aspect 
which it shows in Ayrshire and the west. 
During the progress of the Survey in Ayrshire, we have been 
fortunate enough to bring to light a new page in the history of 
volcanic action in this country — viz., the existence of a remarkable 
series of melaphyres, porphyrites, ashes and volcanic agglomerates, 
interbedded in the Permian series of that county and of Dumfries- 
shire. These rocks are of Permian age, and prove the existence of 
a group of active volcanic vents at that geological period in the 
south-west of Scotland.* In connection with this subject, I may 
mention that we have now accumulated a large body of evidence 
regarding the dates and extent of ancient volcanic action in Scot- 
land. The oldest volcanic rocks we have yet encountered belong 
to the Lower Old Bed Sandstone ; they are well seen in the chain 
of the Ochil Hills, and in the range of broken heights which stretches 
from the Braid Hills at Edinburgh south-westward across Clydes- 
dale and Nithsdale, almost to the coast of Ayrshire. Then comes 
a group which seems to form a middle division in the Old Red 
Sandstone, and is seen in the south of the county of Ayr. The 
* See Geol. Mag. for June 1866. 
