CHAP, xxvin 
PUYS OF A YRSHIRE AND LIDDESDALE 
475 
intervenes between the Carboniferous Limestone and the Coal-measures, and 
from its position appears to mark the latest Carboniferous volcanoes. Its 
component rocks reach a thickness of sometimes 600 feet, and as they dip 
southwards under the Coal-measures, they may extend for some distance in 
that direction. Tliey have been met witli hi borings sunk through the 
northern part of the Irvine coalfield. Even what of them can be seen at 
the surface, in spite of the effects of faults and denudation, shows that they 
form one of the most persistent platforms of volcanic rock among the puy- 
eruptions of Scotland. 
Where best developed this volcanic Itand has a zone of tuff at the 
Ijottom, a central and much thicker zone of bedded basalts, and an upper 
gi’oup of tuffs, on which the Coal-measures rest eonforuiably. A few vents, 
probably connected with it, are to be seen at the surface between Fenwick 
and Ardrossan. But others have been buried under the Carboniferous sedi- 
mentary rocks, and, as already described, have been discovered in the under- 
ground workings for coal and ironstone (p. 434). These mining operations 
have, indeed, revealed the presence of far more volcanic material below 
ground than would be surmized from what can be seen at the surface. 
Here and there, thin layers of tuff appear in brook-sections, indicating what 
might be conjectured to have been trilling discharges of volcanic material. 
But the prosecution of the ironstone-mining has proved that, at the time 
wlien the seam of Blackband Ironstone of that district was accumulated, the 
floor of the shallow sea or lagoon where this deposition took place was dotted 
over with cones of tuff, in tlie hollows between which the ferruginous and 
other sediments gathered into layers. That seam is in one place thick and 
of good quality ; yet only a short distance off it is found to be so mixed 
with fine tuff as to be worthless, and even to die out altogether.' 
3. LIDDESDALE 
A remarkable development of puys lies in that little-visited tract of 
country which stretches from the valleys of the Teviot and Eule Water 
south-westwards across the high moorland watershed, and down Liddesdale. 
Through this district a zone of bedded olivine-basalts and associated tuffs 
runs in a broken band which, owing to numerous faults and extensive 
denudation, covers now only a few scattered patches of the site over which 
it once spread. The geological horizon of this zone lies in the Calciferous 
Sandstones, many hundred feet aliove the position of the top of the plateau- 
lavas (Map IV.). 
So great an amount of material has been here removed by denudation 
that not only has the volcanic zone been bared away, but the vents which 
supplied its materials have been revealed in the most remarkable manner 
over an area some twenty miles long and eight miles broad. Upwards of 
forty necks of agglomerate may be seen in this district, rising through the 
Silurian, Old Bed Sandstone, and lowest Carboniferous rocks. It fills the 
* See Explanation of Sheet 22, Geol. Sun. of Scotland, para. 29, 33, 45. 
