KixAHAX — On Granitic and other Ingenite Hocks. 105 



fig. A, PL 9). These whinstone dykes often occiu' associated with older 

 intmsiye rocks, coming up alongside or in them, on which account in 

 some places rocks of quite different ages are found associated together. 

 A whinstone in a granite vein, and this granite vein in hornblende 

 rock, has been observed in various places. 



Felstojies of post-silurian age. — These felstones are newer than the 

 rocks of Llandovery age ; they come up through the silurian, the meta- 

 morphic, and the granitic rocks. They are blue, gi'eenish-blue, or gi'ey 

 in colour, from compact to splintery, often more or less granular, and 

 with a fi'actiu'e fi'om semiconchoiclal to uneven. In places when 

 traversing certain argillaceous rock there are no walls to the dykes, the 

 two rocks merging into one another as if the adjoining part of the 

 deiivate rock had melted, and thereby been amalgamated with the fel- 

 stone. Some, if not all, these rocks belong to the eurytes or basic fel- 

 stones (one of the hylrid-rochs of Durocher), as splinters fuse on the 

 edge before the blowpipe, some even seeming to graduate into a 

 uiilitic-diabase. Others are porphpitic merging into porphyrite ; the 

 latter more generally being found as small dykes or as thin portions 

 alongside the walls of large dykes. In the latter case although the 

 major portion of the dyke may be grey or green in coloui", splintery 

 or granular in texture, and breaking with an uneven fractiu'e, yet a 

 few inches in thickness alongside the walls will be of a clear blue 

 coloiu- with distinct felspar ciystals (a porphyiite), compact and break- 

 ing with a conchoidal or .subconchoidal fi'actui'e. Some of these fel- 

 stones are so jointy that they break up into an angular shingle or 

 gravel — in some there is a platy arrangement parallel or nearly so to 

 the walls of the dykes, while in others or in parts of others there is an 

 obliqiie structure, and often between the oblique lines are others per- 

 pendicular to them, as shown in fig. C, PL 9. At or near the ter- 

 mination of dykes a spheroidal structui'e is common, more or less 

 combined with a platy aiTangement. 



Felstones of u-pper silurian age (Llandovery). — These felstones occur 

 as bedded masses among the rocks of upper Llandovery age and as dykes 

 in the granitic and other hypogene rocks. Among the Llandovery rock 

 they are associated with tuffs, agglomerates, and such like mechanical 

 accompaniments ; in places the basal-bed of the Toormakeady and 

 Mweeli'ea beds is one of these felstones. Among the hypogene rocks 

 the dykes sometimes graduate into amphiholic-elvanyte. 



These rocks are usually very compact, often comoid ; some, however, 

 are scorious and amygdaloidal ; they may be porphyritic or pass into 

 porphyiite. In places when in bed-like masses they have a columnar 

 structiu'e. They are fi'om green to purple in coloiu' ; often are quartzitic, 

 especially the piu'ple rocks, containing blebs, globules, and crystals of 

 glassy quartz that usually have a dull pellicle. Before the blowpipe 

 they fuse with greater or less facility, the piu'ple varieties on the edges of 

 splinters, but some of the green rock readily into a bead. All the green 

 varieties are veiy basic, some indeed appearing to graduate into wliin- 

 stone. One variety is maculated, rounchsh and oval dark blue patches 



