5 « 
THE PERMIAN VOLCANOES 
BOOK VII 
matrix was noticed. A specimen from Patna Hill consists of “a clear 
irregularly cracked aggregate of carbonates and quartz with hornblende, and 
its structure reminds one of that of olivine. The hornblende is in small 
irregular patches surrounded by the clear mineral, ami is probably a replace- 
ment of a pyroxene, perhaps diallage.” If this stone was once an olivine 
nodule, the agglomerate might in this respect be compared with some of the 
tuffs of the Eifel so well known for their lumps of olivine. 
The stratified tuffs are generally more or less gravelly deposits, composed 
ot lapilli varying in size from mere grains up to pea-like fragments, but with 
numerous larger stones and occasional blocks of still greater dimensions. 
They often pass into a tough dull compact mudstone. In colour they are 
greenish or reddish. They have been largely derived from the explosion 
of lavas generally’ similar to those of which fragments occur in the agglomer- 
ates. They often contain non-volcanic detritus, derived from the blowing up 
of the rocks through which the vents were opened. Occasionally they 
include also various minerals such as pyrope, black mica, sanidine, augite, 
and others which appear to have been ejected as loose and often broken 
crystals. This character is more fully described in regard to its occurrence 
among the necks of the east part of Fife. 
I’he intrusive rocks, probably referable to the same volcanic period, con- 
sist chiefly’ of dolerites and basalts which occur as dykes, sills and bosses, 
and are more particularly developed in the south-west of Ayrshire. 
ii. GEOLOGICAL STRUCTURE OF THE VOLCANIC DISTRICTS 
1. Ayrshire, Nithsdale and Annandale 
(1) Interstratified Lavas and Tuffs . — It will be convenient to consider 
first the volcanic chronicle as it has been preserved in the south-west and 
south of Scotland, where the existence of Permian volcanoes in Britain was 
first recognized. The volcanic rocks in the middle of the Ayrshire coal-field 
. rise from under a central basin of red sandstone, which they completely’ 
enclose. Their outcrop at the surface varies up to about a mile or rather 
more in breadth, and forms a pear-shaped ring, measuring about nine miles 
across at its greatest width (Map V.). 1 
This volcanic ring runs as a tract of higher ground encircling the hollow 
in which the Permian red sandstones lie, and forming a marked chain of 
heights above the Carboniferous country around. It is built up of a 
succession of sheets of different lavas, with occasional partings of tuff or 
volcanic breccia, which present their escarpments towards the coal-field outside, 
and dip gently into the basin under the inner trough of brick-red sandstones. 
Good sections of the rocks are exposed in the ravines of the River Ayr, 
particularly at Ballochmyle, in the Dippol Burn near Auchinleck House, and 
in the railway cutting near Mossgiel. 
1 Mr. Gunn lias recently detected among the newest red sandstones of Arran a small patch of 
volcanic rocks which may be of this age. Mr. A. Maeconochie has also found what may be traces 
of a similar volcanic band below the Permian sandstones of Loch Ryan, in Wigtonshire. 
