66 
THE PERMIAN VOLCANOES 
BOOK VII 
narrow glen of the Carron Water, we observe its boor and sides to be 
covered with the sheets of lava and tuff already noticed. And so travelling 
onward from the vale of the USTith into that of the Capel Water, thence into 
the Water of Ae and across into the great strath of Annandale, we may 
detect, if not actual vents, at least the beds of lava and layers of volcanic 
detritus that were ejected from them. 
All along these valleys, which were already valleys in Carboniferous time, 
traces of the volcanic activity of this epoch may be detected. But, so far 
as I am aware, in not a single case has any vent been observed to have been 
opened on the high surrounding ridges. There has obviously been a 
determining cause why the volcanic orifices should have kept to the plains 
and the main valleys with their tributaries, and should have avoided the 
hills which rise now to heights of 500 to 1000 feet or more above the 
bottoms of the valleys that traverse them. It might be said that the 
valleys follow lines of fracture, and that the vents have been opened along 
these lines. But my colleagues in the Geological Survey, as well as myself, 
have failed, in most cases, to find any evidence of such dislocations among 
the rocks that form the surface of the country, while it is sometimes possible 
to prove that they really do not exist there. 
Though only a few scattered patches of the Permian bedded lavas and 
tuffs have been preserved, enough is left to indicate that the vents were 
active only in the early part of the period represented by the Scottish 
Permian red sandstones, for it is entirely in the lower part of these strata 
that volcanic rocks occur. The eruptions gradually ceased, and the sheets 
of ejected material, probably also the volcanic cones, were buried under at 
least several hundred feet of red sandstone. TV hether or not any portion 
of the erupted material was for a time built up above the level of the water, 
there seems to be no question that the vents were, on the whole, subaqueous. 
3. Sills . — The phenomena of sills and dykes are less clearly developed 
among the Permian volcanic rocks of the Ayrshire basin than among those 
of older formations. In the section exposed in the course of the Paver 
Fig. 206. — Section of sills traversing tlie Permian volcanic series. Paver Ayr, Ballochmyle. 
a, Coal-measures ; I) 6, Basic lavas ; c c, Brick-red sandstones with tuft' ; d, Red tuff and volcanic breccia ; 
e e, Dolerite sills. 
Ayr at Howford Bridge, a coarsely crystalline dolerite which extends for 
nearly 300 yards up the stream, cuts the Permian lavas, of which it 
encloses patches as well as pieces of sandstone. At the contact, the rock 
becomes fine-grained (Fig. 206). Through the coarsely crystalline material 
run long parallel “ segregation veins ” of a paler, more acid substance, as 
among the Carboniferous sills. Similar rocks are well seen in the Dippol 
Burn near Auchinleck House. 
Passing outward into the Coal-measures, we encounter a much larger 
