CHAPTER XIV 
THE SILUKIAN VOLCANOES OF IKELAND 
Abundant as are the volcanic records of the Silurian period in England, 
Wales and Scotland, the description of them would be incomplete without 
an account of those of Ireland. The eruptions of Arenig, Tdandeilo and 
Bala time, which we have followed from the south of Caermarthenshire to 
the borders of the Scottish Highlands, had their counterparts all down the 
east of Ireland. The Irish register of them, however, supplies some details 
which are less clearly preserved in the sister island. But tlie most distinct- 
ive feature of the Silurian volcanic history in Ireland is the preservation 
of memorials of eruptions during the Upper Silurian period. In no part 
of Great Britain has any unquestionable trace been found of volcanic activity 
during that part of the geological record, the last eruptions of which the age 
is known being those of the Bala rocks. But in the south-west ot Ireland 
there is evidence that for a time active vents appeared over the sea-lioor on 
which the earlier deposits of Upper Sihirian time were laid down. 
I. The Lower Silurian Series 
i. Unqjfiona prohcMij of Areniff A(jc 
It is in that part of Ireland which lies east of a line drawn from Strahane to 
Dungarvan Harbour that the records of Lower Silurian volcanic activity are to 
be found. In the north the development of volcanic rocks resembles that in 
Scotland, in the south it corresponds rather with the volcanic districts of Wales. 
The Irish Silurian volcanic rocks have been traced with more or less 
detail on the maps of the Geological Sur\'ey. Since these maps were 
published, however, great advances have been made in the study of the 
petrography of volcanic rocks, as well as in the art of tracing their structure 
upon maps. Much, therefore, now remains to be done to bring our know- 
ledge of the older volcanic history of Ireland abreast of that of the rest of 
the British Isles. In the following summary I have had to rely mainly on 
my own traverses of the ground, guided by the maps and memoirs of the 
Survey, and with the personal assistance of some of my colleagues. 
The remarkable zone of crushed cherts, igneous rocks and sandstones. 
