40 
the carboniferous volcanoes 
BOOK VI 
stone and chert occur in the breccia. The hand of stratified rock, if in 
situ may be a tongue projecting from the wall into the body of the neck 
like some instances already cited from Scotland, but more probably 7is 
as efsewherf ™ ^ within vent itself. The breccia here 
as elsewheie is entirely without any trace of stratification. The second 
wLTTpit “ ,T,“ “* ""* h ” f °«*> -here the 
roestones, rapidly undulating, seem at last to plunge below the breccia. 
BuTtheleTiaA ° f • P f ralIeI divisional P lanef * suggestive of bedding’ 
component *"* “ « #» 
In the necks, and also through the limestone surrounding them masses 
ma2 l of r T b6en intlUded aS bosses and veink The 
material of these intrusions presents little variety, and, so far as I could 
dSienTLa 110 -cessive profusion of progress!^ 
doEte ibere tZ T* 7“ ‘ ^ blue - bIack fin ^aine«l basalt to a 
clolente where the plagioclase is distinct. Some portions, however are 
moie basic and pass into limburgite. Externally there is nothin^ worthy 
stiucture. The amygdales, generally of calcite, vary from small pea-like 
or more in the dolerites. 
f, . v ’ O — V V cl 
harms m the basalts up to kernels half an inch long ,, 
eXa T ati0n Mr - Wafcts “that some of the basalts 
Ohvritic tl P T and auglfce rich in brown mica, and that their por- 
phyritic felspars enclose idiomorphic crystals of augite 1 
serief f?b? he “ notieeable feature in fchese later parts of the volcanic 
umus of a h them at oae “ty in Croghan Demesne of 
rod These ^ Cry a llne material f l uite distinct from the surrounding 
dhmeter Tl!" Tl" 1 ’ 7 *T “ ° r two to a *** - more if 
• “ f iiey must be regarded as blocks which have been carried up 
Mr mr • S1C kVa - Their imposition has been ascertained by 
Mr. Watts from microscopic examination to be somewhat singular One 
pecmien contains relics of garnets, surrounded by rings of kelyplhte 
imbedded m a mosaic of felspar, with a mineral which may possibly be 
S^nt^r TT fr ° m ^ 8ame loca % (south-east from Gor- 
n) contains the relics of garnets preserved as kelyphite, set in a matrix 
"reenish Z "vell inS ’ f ra “ edj and eontainin g a profusion of crystals of 
rock and m i ° r "? ™ S ap P ears to ba a metamorphic 
rocks.” i ^ 36 a fragment oi some sediment enclosed in the igneous 
. r ® gards the histor 7 of volcanic action in Britain one of the chief 
poin s °f interest connected with these Irish breccias and lavas rd^ 
of the U ^ e ° ° glCal age ‘ As 110 proof lms 1)een Produced that any portion 
stone wh- S h C ° n mP T ne ° U8]y in terstratified the Carboniferous Lhne 
s one which surrounds them, we cannot definitely affirm that the volcanic 
eruptions which they record took place during the accumulation of Xt 
t0tke «*****"*• * * 
