CHAP. XIV 
LLANDEILO AND BALA ERUPTIONS OF IRELAND 
251 
possible to conceive that these conditions conld have been confined to the 
extreme south of Ireland. We should certainly expect to ^ meet with 
evidence of them elsewhere, at least in the same bihiiian region. 
While I hesitate to express a decided opinion in opposition to the 
conclusions of such experienced observers as Jukes and Du Noyer, I incline 
to believe that the rocks in question really belong to the Old Ked Sandstone. 
If such shall finally be determined to be their geological position, they will 
supply evidence that some at least of the volcanic vents of the coast-line 
cannot be older than the Old Eed Sandstone. They are pierced by masses 
of soda-felsite and by a coarse red agglomerate containing abundant pieces 
of felsite. These volcanic rocks belong to the same type as those whic 1 
break through the undoubted Silurian rocks on either side. They may 
thus come to prove a recrudescence of volcanic energy in this same district 
at a much later geological period ; and a new problem will arise to task the 
skill of the most accomplished field-geologist and petrographer— to unravel 
the structure and history of this chain of volcanic vents, and, in so doing 
to detect and separate the eruptions of Lower Silurian time from those ot 
the Lower Old lied Sandstone. 
In the far west of Ireland, another group of Lower Siliu'ian volcanoes has 
left its remains in the mountainous tract of country between the western 
shores of Lough Mask and Killary Harbour.^ There appear to have been at 
least three separate centres of eruption along a line stretching in .yorth- 
easterly direction for about 16 miles from the western end of Lough Nafooey 
to the hamlet of Dcrrindaffdery beyond Toiirniakeady, where the older rocks 
are uneonformably overlain by the lower Garboniferous strata. As shown 
by the mapping of the Geological Survey, the most northerly area, whicli 
may be called the Tourmakeady centre, has a breadth of about a niile, and 
dies out southward after a course of nearly six miles. About a mile to the 
south-west of the last visible prolongation of its rocks, we encounter a second 
volcanic centre which occupies an area of about a square mile in the va ey 
of Glensaul. The third centre stretches from the western shores of Long 1 
Mask across Lough Kafooey, where it forms a mass of high rugged ground, 
and reaches a lengtli of some six or seven miles before it finally dies out. 
1 The nearest approach of any Silurian group of st«ta 0 
is furnished by the remarkably coarse conglomerates, boulder-heds and pebbly giits ^ Bala 
and uSove^y series in the region between Killary Harbour and Lough Mask, to which fuithei 
reference is made, in a later part ““Ijl^’^^ian series by the officers of the Geological Survey who 
- This group was ‘ b 1 - Geological Map of Ireland and accompanying 
mappedthereglo^seeSheetsad 8.5, J4anl9o^^^^ 
Explanation), and on their ^ that the limestone associated with the lavas 
Silurian age. Mr. Baily ^d pakeontological testimony, the fossils 
and agglomerates contains B^ lossds^ of formations to 
were considered to be “ derivative, ana me . . .. a « 
which they would naturally be assigned. A recent examination ol the 
Mr. J. R. Kilroe of the G^logical Survey, has satis^d me that the vol aiiic lock .ire ite 
stratified with sedimentary deposits of Bala age, and must consequent y be 
rest of the Lower Silurian series of Ireland. The results of this examination are given - ^ ^ 
a The.se areas were carefully mapped for the Survey by Mr. f^o an, and the lines of 
marked by liim fairly represent the general distribution of the rocks. 
