CHAP. XXII 
ERUPTIONS IN SOUTH-WEST IRELAND 
349 
have been brought up to the surface. Two such ridges of Upper Old Ked 
Sandstone hear, each on its crest, a small hut interesting relic of volcanic 
activity^ (Map I.). 
The more northerly ridge rises in the conical eminence ot Knock- 
feerina to a height of 949 feet above the sea. Even from a distance tlie 
resemblance of this hill (Fig. 102) to many of the Carboniferous necks of 
Scotland at once attracts the eye of the geologist. The resemblance is 
found to hold still more closely when the internal structure of the ground is 
examined. The cone consists mainly of a coarse agglomerate, with blocks 
generally somewhat rounded and varying in size up to two leet in length. The 
most prominent of these, on the lower eastern slopes, are pieces of a fine Hint}’ 
felsite weathering white, hut there also occur fragments of grit and baked 
shale. The matrix is dull-green in colour, and among its ingredients are 
t'lG. 102. — View of Knockfeerina, Limerick, from Uie iiorth-e.ast — .1 volcanic neck of 
Upper Old Ked S.audstoiie age. 
abundant small lapilli of a finely vesicular andesite or diabase. These 
more basic ingredients increase in number towards the top of the 
eminence, where much of the agglomerate is almost wholly made up of 
them. No marked dip is observable over most of the hill, the rock appear- 
ing as a tumultuous agglomerate, though here and there, particularly near 
the top and on the south side, a rude bedding may be detected dipping- 
outwards. On the west side the agglomerate is flanked with yellow sand- 
stone baked into quartzite, so that the line of junction there between the 
two rocks not improbably gives us the actual wall of the vent. The 
induration of the surrounding sandstones is a familiar feature among the 
Carboniferous vents. Some intrusive dark flinty rock traverses the agglom- 
erate near the top on the north side. 
lietiring eastwards from the cone, the observer finds evidence of the 
intercalation of tuff among the surrounding Upper Old Bed Sandstone. At 
the east end of the village of Knockfeerina a red nodular tufi', with roimded 
pieces of andesite, grit and sandstone, sometimes 12 inches long, is seen 
to dip under yellow, grey and red sandstones and shales, while other shales 
1 See Sheet 153 of the Geological Survey of Ireland, and Explanation to that Sheet (1861), by 
Messrs. G. H. Kinahan and J. O’Kelly. The account of the ground above given is from notes 
which I made during a personal visit. 
