33 : 
VOLCANOES OF THE LOWER OLD RED SANDSTONE book v 
Owing to complicated faiilts, extensive nncoufotmable overlaps of the 
Oarboniferons formations, and enormons denudation, tlie volcanic tracts of 
Ohl Red Sandstone age in Ayrshire have been reduced to mere scattered 
patclres, the true relations of whicli are not always easily discoverable. One 
of these isolated areas Hanks the Silurian Uplands as a belt from a mile to 
a mile and a ladf in breadth and about six miles long, but with its limits 
everywhere defined by faults. A second much more diversified district 
exteiuls for about ten miles to the soutli-west of Dalmellington. It too 
forms a belt, averaging about four miles in breadth, but presenting a singularly 
complicated geological structure. Owing to faults, curvatures and denuda- 
tion, the volcanic rocks have there been isolated into a number of detached 
portions, between some of which the older parts of the Old Red Sandstone, 
and even the Silurian rocks, have been laid bare, while between others the 
ground is overspread with Carboniferous strata. A third unbroken area 
forms the Brown Cai'rick Hills, south of the town of Ayi', and is of special 
interest from the fact that its rocks have been exposed along a range of sea- 
cliffs and of beach-sections for a distance of nearly four miles. Other detached 
tracts of volcanic rocks are displayed on the shore at Tui’iiberry and Port 
Garrick, on the hills between Mochrum and the vale of the Girvan, and on 
the low ground between Daliymple and Kirkmichael. 
The isolation of these various outliers and separated districts is probably 
not entirely due to the effects of subsequent geological revolutions. More 
probably some of the areas were always independent of each other, and their 
igneous i-ocks were discharged from distinct volcanic centres. We may 
conjecture that one of these centres lay somewhere in the neighbourhood of 
New Cumnock, for the lavas between that town and Dalmellington appear 
to diminish in thickness and numlier as they are traced south-westward. 
Another vent, or more probably a group of vents, may have stood on the 
site of the present hills to the right and left of the Girvan Valley, south of 
the village of Straiton. A third probaldy rose somewhere between l)ailly 
and' Crosshill, and poured out the lavas of the ridges between Maybole and 
the Dailly coal-field. The important centre of eruption that produced the 
thick and extensive lavas of the Brown Garrick Hills may be concealed 
under these hills, or may have stood somewhere to the west of Maybole. 
Still another vent, perhaps now under the sea, appears to be indicated by 
the porphyrites of the eoast-scction between Tuniberry and Culzean Bay. 
Owing to the complicated structure of the ground, several important 
points in the history of the Old Red Sandstone of this region have not been 
established beyond dispute. In particular, the unconformability which un- 
doubtedly exists in that system in the south-west of Ayrshire has not 
been traced far enough eastwards to determine whether it affects the volcanic 
belt east ol Halmellington, or whether the break took place before or after 
the eruption of that belt. V^est ol Dalmellington it clearly separates a 
higher group of sandstones, conglomerates and volcanic rocks from every- 
thing older than themselves. The structure is similar to that in the Pent- 
land Hills, a marked disturbance having taken place here as well as 
