CHAPTER XXX 
the CARBONIFEROUS VOLCANOES OF IRELAND 
King’s County— The Limerick Basin— The Volcanic Breccias of Doubtful Age in 
County Cork. 
Although the Carboniferous system spreads over by far the larger part of 
tlle surface of Ireland, and is laid bare in many thousands of natural and 
artificial sections it displays undoubtedly contemporaneous igneous rocks, so 
far as at present known, at only one locality— the region around Limerick. 
A second district, however, lies in King’s County, where some vents occur 
w hieh may be of Carboniferous age, and of which a description will be given 
the following pages. That the relics of volcanic action should be so few 
w hile the exposures of the Carboniferous formations are so numerous and 
So completely disclose the geological history of the whole system, must >e 
Regarded as good evidence that while volcanoes abounded and continued 
"*g active in Scotland and in parts of the Centre and South-west of England 
hardly appeared at all in Ireland. It is worthy of remark, also, that 
tlle Irish eruptions belong to the time of the Carboniferous Limestone— a 
Ifiod distinguished by volcanic activity in Scotland and England— that 
nature of the materials erupted bears a close resemblance to that ot the 
J av as and tuffg of the 8ister island, and that the manner of their eruption 
a close counterpart in the Puy-eruptions, already described. 
1. king’s county 
In the progress of the Geological Survey several small tracts of “ green- 
st °ne ash” and “greenstone” were mapped within an area ol a few square 
1Ulles lying to the north of Philipstown. These igneous rocks were shown to 
° rra Croghan Hill, which, rising into a conical eminence 769 feet above the 
Sea> a nd some 450 feet above the general level of the great limestone plain 
ar °nnd it, forms the only conspicuous feature in the landscape for many 
miles - In the maps and their accompanying Explanations, the “greenstones 
' U ' e Seated as intrusive masses, but the “ greenstone ash ” or breccia appears 
0 have been regarded as interstratified in the Carboniferous Limestone, 
