179 
Geological Relations of the East of Ireland . 
the felspar crystals and hornblende are very distinct. The northern 
part of the hill consists in general of greenstone, bluish grey of 
various shades, containing common and magnetic pyrites dissemi- 
nated; but in the southern, felspar porphyry predominates, com- 
posed of a compact base of felspar tinged in some places with 
hornblende, and containing inlaid crystals of felspar and spots of 
hornblende. This last mentioned rock is at times traversed by 
numerous contemporaneous veins of quartz, as may be seen on the 
eastern side, where some of them are of short extent and terminate 
in slight threads. On this side also, the greenstone exhibits some 
small veins and interwoven portions of calcareous spar. High up, on 
the north-western side of the hill, in the interval where greenstone 
graduates into felspar, a variety may be observed, which is well 
entitled to the name of basalt. It is very similar to the basalt of 
the Giant’s Causeway; a blackish grey, dense, uniform substance, 
close in grain, presenting minute facets variously disposed.* 
On the south-eastern side of the hill, the felspar rock displays 
small short columnar distinct concretions, irregularly waved, with 
a tendency to the six-sided form, in a nearly vertical position. 
They much resemble those small irregular columnar concretions, 
* It may perhaps not appear superfluous to remind those philosophers, who maintain the 
igneous origin of basalt, that this rock is not the exclusive product of any peculiar soil, 
but, is, on the contrary, the inmate of every class of rocks. Thus, basalt is found inter- 
stratified with granite, gneiss, and mica slate. (See Charpentier’s observations on the 
repositories of ores ; a work equally interesting and valuable to the miner and geologist. 
See also Gerhard, Reuss, and Von Buch.) It occurs interstratified with clay slate and 
quartz rock. (See the observations of Gerhard, Leske, and Karsten.) It alternates 
with greywacke and clay slate, in the transition country on the banks of the Lower 
Rhine, which serves as a basis to the overlying trap formation and extinct subterranean 
fires. (See Nose’s Travels on the Lower Rhine.) The occurrence of basalt as an inmate 
of the floetz class, and also as a member of the overlying trap formation, is too well known 
to require more than the simple notice of the fact. 
Z 2 
