CHAP. XXXI 
A YRSHIRE AND NITHSDALE 
55 
The comparatively feeble and short-lived volcanoes now to be described 
are found in two regions wide apart from each other. The more important 
of these lies in the south-west and centre of Scotland. A second group 
rose in Devonshire. It is possible that a third group appeared between 
these two regions, somewhere in the midlands. The evidence 01 ie 
history of each area will be given in a separate section m the following 
pages. 
i. GENERAL CHARACTERISTICS NATURE OF MATERIALS ERUPTED 
The chief district for the display of volcanic eruptions that may be 
assigned to the Permian period lies in the centre of Ayrshire and t ie 
valleys of the Nith and Annan. But, for reasons stated below, I sha 
include within the same volcanic province a large part of the eastern 1a 
of the basin of the Firth of Forth (see Map. A •)■ ... 
Unfortunately the interesting volcanic rocks now to be considers ia 
suffered severely from the effects of denudation. They have been entirely 
removed from wide tracts over which they almost certainly once extended. 
But this enormous waste has not been wholly without compensations. 
The lavas and tuffs ejected at the surface, and once widely spread over it 
durin" the deposition of the red sandstones, have been reduced to merely a 
few detached fragments. But, on the other hand, their removal asa^ 
ficial covering lias revealed the vents of discharge to an extent unequalled 
in any older geological system, even among the puys of the Carbom ^ 
period The Permian rocks, escaping the effects of those great earth- 
movements which dislocated, plicated and buried the older labeozoic 
systems of deposits, still remain for the most part approximately horizontal 
or only gently inclined. They have thus been more bab e to complete 
removal from wide tracts of country than older formations which have been 
protected by having large portions of their mass carried down by extensive 
faults and synclinal folds, and by being buried under ater sedimentary 
accumulations. We ought not, therefore, to judge of the extent of the 
volcanic discharges during Permian time merely from the small patches of 
lava and tuff which have survived in one or two districts, but rather fioi 
the number, size and distribution of the vents which the work of denuda- 
tion has laid bare. . . „ 
The evidence for the geological age of the volcanic series now 
described is less direct and obvious than most of that with wine 1 ia ^ 
been hitherto dealing. It consists of two kinds, (a) In the first of these 
conies the series of lavas and tuffs just referred to as regularly mtei- 
stratified with the red sandstones, which, on the grounds given m the next 
paragraph, it is agreed to regard as Permian, (b) Connected whh thes 
rocks are necks which obviously served as vents for the discharge of t 
volcanic materials. They pierce not only the Coal-measures but even parts 
of the overlying bedded lavas. So far there is not much room 'or diffcr^ce 
opinion ; but as we recede nortliwar I from Ayrshire and Nitlisdale, where the 
