Vol. 68.] PALiEOZOIC KOCKS OE THE KILBEIDE PEIflNSULA. 79 



explosive origin, flow-breccias are not unfrequently met with in 

 the spilites. 



The coarseness of the breccias renders it, as a rule, impossible to 

 ascertain their dip and strike, but occasionally interbedded fine 

 bands give the direction : as, for example, at a point 400 yards 

 north-east of Lough Mweelaun, a band of grit interbedded in the 

 breccia has a north-westerly and south-easterly strike, while 250 

 yards west-south-west of this point very thin bands of chert and 

 fine ash strike in the same general direction. 



The numerous little patches of breccia mapped among the spilites 

 may often be larger than is indicated in the map, the ground being 

 much obscured by peat. An important feature in which the 

 Kilbride district differs from those of Tourmakeady and Glensaul 

 is the complete absence of limestone-breccias — in fact, of calcareous 

 Ordovician rocks of all kinds. 



It is noteworthy that the breccias to the south-west of Lough 

 Mweelaun show the introduction of a considerable amount of chert, 

 which has been deposited round the felsite-blocks so as sometimes 

 to enclose them completely. This fact is of importance, in con- 

 nexion with the method of introduction of chert among the 

 spilites. Xo chert-fragments were noticed among the tuffs of 

 the Kilbride district, although such fragments are common among- 

 the limestone-breccias of the Tourmakeady district. 



(c) The Spilites (Pillow-Lavas). 



In our earlier paper on the rocks of the Tourmakeady district, we 

 described as intrusive certain spilites — fine - grained rocks of 

 andesitic character, and quoted (Q. J. Gr. S. vol. Ixv, 1909, p. 136) 

 Dr. J. S. Flett, who, subsequently to the reading of the paper,, 

 kindly examined the rocks, as pointing out their strong resem- 

 blance in microscopical structure to certain pillow-lavas. In the 

 Tourmakeady district these rocks, which are very poorly exposed, 

 apparently form small intrusions and show no pillows. But rocks 

 of the same type exhibit a vastly greater development in the Kilbride 

 area, forming its most remarkable feature ; and at very numerous 

 points a pillow-structure is finely seen, the diameters of the pillows 

 generally varying from 18 inches to about 3 feet. 



Spilites cover a larger area than any other rock in the Kilbride 

 peninsula. Commencing at a point near the top of Knock Kilbride, 

 they extend westwards in a broad band, interrupted in places by 

 patches of breccia, to the Pinny Eiver, where their outcrop has a 

 width of half a mile. The rocks between the Oak Island Fault 

 and the felsite-mass of Glenbeg are also predominantly spilites, and 

 are here interbedded with breccia and with a band of grit which 

 bisects the westernmost of the two smaller felsite-masses in this 

 area. 



Although, as a rule, there is no clear line of strike to be observed 

 in the spilites, this is commonly obtainable from the interbedded 



