CHAPTER XXII 
VOLCANOES OF THE UPPER OLD RED SANDSTONE — THE SOUTH-WEST OF 
IRELAND, THE NORTH OF SCOTLAND 
In the northern lialf of Britain, where the Old Eed Sandstone is so well 
dis])lfiyed, the two great divisions into which this series of sedimentary 
deposits is there divisible are separated from each other by a strongly marked 
unconformability. The interval of time represented by this break must 
have been of long duration, for it witnessed the effacement of the old 
water- basins, the folding, fracture, and elevation of their thick sedimentary 
and volcanic accumulations, and the removal by denudation of, in some 
places, several thousand feet of these rocks. The Upper Old Eed Sand- 
stone, consisting so largely as it does of red sandstones and conglomerates, 
indicates the return or persistence of geographical conditions not unlike 
those that marked the deposition of the lower subdivision. But in one 
important respect its history differs greatly from that which I have 
sketched for the older part of tlie system. Thougli the Upper Old Eed 
Sandstone is well developed across the soutliern districts of Scotland from 
the Ochil to the Clieviot Hills, and appears in scattered areas over so much 
of England and Wales, no trace has ever been there detected in it of any 
contemporaneously erupted volcanic rocks. The topographical changes 
which preceded its deposition must have involved no inconsiderable 
amount of subterranean disturbance, yet the volcanic energy, which had 
died out so completely long before the close of the time of the. Lower Old 
Eed Sandstone, does not appear to have been rekindled until the beginning 
of the Carboniferous period. 
Two widely separated tracts in the British Isles have yielded traces of 
contemporaneous volcanic rocks in the Upper Old Eed Sandstone. One 
of tliese lies in the south-w'est of Ireland, the other in the far north of 
Scotland. 
THE .SOUTH-WEST OF IRELAND 
The Irish locality is situated a few miles to the south of the town of 
Limerick, where the Carboniferous Limestone has been thrown into long 
folds, and wdiere, along the anticlines, strips of the underlying red sandstones 
