CHAP. XXI 
ERUPTIONS AT KILLARNEY 
347 
of which took place not many miles to the west, in the Dingle promontory. 
But elsewhere this type ‘does not appear to have survived the end of the 
Silurian period. 
The detrital rocks accompanying the felsite, in the district east of 
Killarney, vary from such closed-grained felsitic material as cannot readily 
he distinguished from the felsite itself to unmistakable felsitic breccias. 
Even in the finest parts of them, occasional rounded quartz-pebbles may 
be detected, while here and there a reddish shaly band, or a layer of fine 
pebbly conglomerate with quartz-pelibles an inch in length, shows at once 
the bedding and the dip. Mr. W. 'W. Watts, who, with Mr. A. M'Henry of 
the Irish Staff of the Geological Survey, accompanied me over this ground, 
found that a microscopic examination of the slides which were prepared 
from the specimens we collected completely confirmed the conclusions 
reached from inspection of the rocks in the field.* He detected among the 
angular grains slightly damaged crystals of felspar, cliiefly orthoclase. 
Many portions of these felspathic grits much resemble the detrital Camlnian 
rocks which in the Vale of Llaiiberis have been made out of the pale felsite 
of that locality. 
’ Mr. Watts also examined the microscopic structure of the felsite of Benaun More. He 
found that the spherulites appear to have a mieropegmatitic structure, oiving to the intergrowth 
of quartz and felspar. In some parts of the rook the spherulites, from "02 to '01 inch in diameter, 
are surrounded by exceedingly minute green needle.s, possibly of hornblende, while inside some 
of them are .small quartz-grains. Larger porphyritic felspars occur outside the spherulites, some 
being of plagioclasc, but most of oi-thoclase. The sphenilitic structure is not so well developed 
near the felspars. A few of the large nodules are hollow and lined with ciy.stals, while some of 
them show a finely concentric landnation like the successive layers of an agate. 
