CHAP. XXIII 
DISTRIBUTION IN BRITAIN 
359 
Not only were the Carboniferous volcanoes most abiindant and persistent 
ill Scotland, but they attained there a variety and development which give 
their remains an altogether exceptional interest in the study of volcanic 
geology. They were distributed over the wide central valley, from the 
south” of Cantyre to beyond the mouth of the estuary of the Forth. On the 
southern side of the Silurian Uplands, they were likewise numerous and 
active. There is thus no considerable tract oi Lower Carboniferous rocks in 
Scotland wdiich does not furnish its evidence of contemporaneous volcanic 
action. 
Although some portions of the Scottish Carboniferous igneous rocks 
run for a short distance into England, it is remarkable that, when these 
at last die out southwards, no other relics of contemporaneous volcanic 
energy take their place. Along the Pennine chain, from the Border into 
the heart of England, though natural sections are abundant, no trace of 
included volcanic rocks appears until we reach Derbyshire. The whole 
of that wide hiterval of 150 miles, so far as the present evidence goes, 
remained during Carboniferous time entirely free from any volcanic eruption. 
But from the picturesque country of the Peak southwards, the sea-floor of 
the Carboniferous Limestone, in what is now the heart of England, vyas 
dotted with vents whence the sheets of “ toadstone ” were ejected, which 
have so long been a familiar feature in English geology. Beyond this 
limited volcanic district the Carboniferous formations of the south-west 
of England remain, on the wliole, devoid of conteniporaneous volcanic 
intercalations, traces of Carboniferous volcanic action having been recognized 
only in West Somerset and Devonshire. In the Mendip district and in the 
ridcres of limestone near Weston-super-Mare bands of cellular lava and tuff 
have been observed. To the west of Dartmoor, Brent Tor and some of the 
surrounding igneous masses may mark the positions of eruptive vents during 
an early part of the Carboniferous period. 
At the south end of the Isle of Man relics remain of a group ot 
vents among the Carboniferous limestones. Passing across to Ireland, 
where these limestones attain so great a thickness and cover so large 
a proportion of the surface of the island, we search in vain for any 
continuation of the abundant and varied volcanic phenomena of Central 
Scotland. So far as observation has yet gone, only two widely separated 
areas of Carlioniferous volcanic rocks are known to occur in Ireland. One 
of these shows that a little group of vents probably rose from the floor of 
the Carboniferous Limestone sea, near Philipstown, in Kings County. The 
other lies far to the west in the Golden Vale of Limerick, where a more 
important series of vents poured out successive streams of lava with showers 
of ashes, from an early part of the Carboniferous period up to about the 
beginning of the time of the Coal-measures. 
The total area within which the volcanic eruptions of Carboniferous 
time took place was thus less than that over which the volcanoes of the 
’ The supposed Carboniferous volcanic rocks of Bearhaven on the coast of Cork are noticed on 
p. 49, vol. ii. 
