422 
THE CARBONIFEROUS VOLCANOES 
KOOK VI 
Watts. One of the most interesting varieties, which occurs at the Standing 
Stone near Oola, was found by hini to show quartz enclosing ophitically tlie 
felspars which, with well-terminated prisms, project into it. Further west, 
near Knockaunavoher, another boss occurs with conspicuous quartz. These 
rocks have much in common with trachytes but have a wholly crystalline 
structure. They will be described in the account of the Limerick basin. 
V,. Tuffs 
The fragmental rocks connected with the puy- eruptions form a well- 
marked group, easily distinguishable, for the most part, from the tuffs of 
the plateaux. They vary from exceedingly fine compacted dust or volcanic 
mud, through various stages of increasing coarseness of texture, to basalt- 
conglomerates and tumultuous agglomerates. 
1 he fragmentary material found in the necks of the puys is generally 
an agglomerate of a dull dirty-green colour. The matrix ranges from a 
fine compact volcanic mud to a thoroughly granular detritus, and sometimes 
shows a spheroidal concentric structure in weathering. In this matrix the 
lapilli are distributed with great irregularity and in constantly varying 
proportions. They consist in large measure of a pale yellowish-green, some- 
times pale grey, very basic, finely vesicular, devitrified glass, which is gener- 
ally much decomposed and cuts easily with the knife. This highly basic 
substance is a kind of palagonite. So minute are its vesicles that under 
the microscope a thin slice may present a delicate lace- like network of 
connected walls, the palagonite occu2>yiug much less space than the vesicles, 
'fhe material has been a finely frothed-up pumice. 
Besides this generally distributed basic pumice, the stones in the 
agglomerate of the necks likewise include fragments of older volcanic grits 
01 tuffs, blocks of basalt or diabase, as well as pieces of the Carboniferous 
strata of the district, especially shale, sandstone and limestone. Xot 
infrequently also, they comprise angular blocks of fossil wood. 
I he materials which fill the necks are generally much coarser than 
those that form intercalated beds. But while in numerous cases huo-e 
blocks of basalt and large masses of sandstone, shale, limestone, ironstone or 
other strata may be seen wrapped up in a matrix of coarse basalt-tuff, in 
not a few instances the material in the necks may be observed to consist 
of a tuff quite as fine as that of the interstratified bands. Such necks appear 
to mark the sites of tuff-cones where only fine ashes and lapilli were ejected, 
and where, after sometimes a brief and feeble period of activity, the orifice 
became extinct. 
Ihe bedded tuffs interstratified with the ordinary Carboniferous strata, 
do not essentially differ in composition from the material of the necks. 
I hey are basalt- (diabase-) tuffs and basalt- (diabase-) conglomerates, usually 
dull green in colour and granular in texture, the lapilli consisting in great 
measure of various more or less decayed basalts, Init containing the same 
highly vesicular basic glass or pumice above referred to. They are mainly 
