3i6 
VOLCANOES OF THE LOWER OLD RED SANDSTONE book v 
measure 18 inches in diameter, and all are well 'water- worn. Immediately 
over this mass of detritus lies the lowest sheet of andesite-lava (d). 
Fig. 84. — Section of the base of the volcanic series, Reclain, live miles south of Pomeroy. 
Some sections visible in the neighbourhood of Omagh afford further 
evidence of volcanic action at the time of the deposition of the Old Eed 
Sandstone of this region. At Farm Hill, a little to the east of the town, 
felspathic sandstones and breccias enclose angular and subangular pieces of 
various andesites, and occasionally even pieces of tuff. Xeai- these strata a 
decayed andesite occurs in the bed of a stream, and a fresher variety is 
([uarried at Farm Hill. A little further south another variety of andesite 
is exposed in two quarries at fiecarson Meeting-House — a fine granular 
purplish-grey rock, with abundantly -diffused htematite 
pseudomorphs, probably after a pyroxene, and sometimes 
strongly amygdaloidal. 
There can thus be no doubt that this region of Ulster 
included several centres of volcanic activity during the 
deposition of the red sandstones and conglomerates, and 
that the lavas and volcanic conglomerates Ijelonged to 
precisely the same types as those of the same geological 
age which occur so almndantly in Scotland. 
Further south-west, near Boyle, in the county of 
Eoscommon, certain curious felspathic breccias in the Old 
Eed Sandstone have been mapped as “ felstone.” ^ So far 
as I have been able to examine them, however, they are 
entirely of fragmental origin. They contain pieces of 
andesitic and felsitic rocks, with fragments of devitrified 
Fk!. 85. Section of alass, whicli undoubtedly point to the occurrence of 
iit" Ci-os'siia Chapel, volcanic eruptions during their deposition, though no 
north-east of Boyle, ^^ffg lavas appear to crop out in the narrow strip of 
“ shui™?™ sremi fomiatioii tlicrc exposed. 
and grey licanl sand- 
stones and grits, some 
bands strongly fel- 
.spatlnc; c, tine cnm- 
7)act felspathic breccia, 
with angular chip.s of 
different felsites and 
andesites, etc. 
The accompanying section (Fig. 85) may he seen on 
the hills to the north-east of Boyle. tYhere quarried 
on the roadside to the north of Boyle, the series 
of deposits liere represented contains a bed of coarse 
and exceedingly compact breccia, similar to that just 
referred to, but containing angular and subangular fragments six or eight 
inches long. The joints of these compact strata are remarkably sharp and 
clean cut, so that where the fragmentary character is not very distinct 
tlie rocks might easily he mistaken on casual inspection for felsites. 
’ See Sheet 66 Geological Survey of Ireland, and E.-cplanatioii to that sheet (1878), p. 15. The 
rocks were previously described by ,Tukes and Foot, Journ. Roy. (leol. Soe. Ireland, vol. i. (1866), 
p. 249. 
