80 ME. C^ARDIXEK AND PROF. EEYXOLDS OX THE [Feb. I9I2, 



bands of breccia, and in several cases from the trend of the bands 

 of pillows. Less frequently, information is afforded by the associated 

 bands of sediment, as in the following five cases : — 



(i) The spilites west of the Oak Island Fault are underlain by a narrow 



band of grit, seen immediately to the west of the more westerly 



of the two small felsite-iutrusions. 

 (ii) Half a mile east-north-east of Lough Mweelaun bauds of chert occur 



interbedded with spilites. 

 (iii) A band of chert, occurring about 150 yards north-west of Lough 



Mweelaun, close to the boundary of the lower spilite-band and 



overlying breccia, strikes parallel to the line of junction between 



the two I'ocks and proved, like some of those of the G-lensaul area, to 



be fine silicified tuff, 

 (iv) About 350 yards east-north-east of the exposure just mentioned a 



band of grit is seen, 

 (v) Chert and crushed shales occur in the bed of the stream a third of a 



mile north-north-west of Finny Chapel, along the line of fault 



between the spilite and the felsite. 



In the area vrest of the Oak Island Fanlt and west of the 

 Lough Mweelaun Fault there are again large areas of spilite. 



The spilites are green or purple rocks, generally dark but some- 

 times of a light colour. They are very commonly vesicular, often 

 markedly so, and when the pillows are exposed in section they are 

 frequently seen to be more vesicular round the margin than towards 

 the centre, or to have bands of concentrically-arranged vesicles (see 

 PI. YII, fig. 1). In many cases, however, the vesicles are irregularly 

 scattered throughout. The most readily accessible spot where the 

 pillows are well seen is near where the rough track to Derrypark 

 leaves the Finny road. Fairly good examples occur in the enclosure 

 behind the priest's house at Finny. Pillows are also finely seen at 

 a number of points along the northern outcrop of the broad band 

 of spilite which stretches north-westwards from near Lough Mwee- 

 laun, and east and west of the prominent dolerite-dyke which runs 

 up the hillside about a third of a mile south-east of this Lough. 

 Here the pillows are intimately associated with spiiite-breccia — 

 a clear case of flow-brecciation. Such brecciation, in this case 

 unaccompanied by pillow-structure, is well seen at a spot on the 

 left bank of the stream a third of a mile north-north-west of 

 Finny Chapel. 



An important feature, in which these pillow-lavas resemble 

 those of the Ballantrae district, is their close association with chert, 

 which is very frequently plentiful. The method of occurrence 

 varies : as a rule, the chert forms a series of irregular strings 

 and patches (see PL VII, fig. 2). But it may occur filling the 

 spaces between the pillows, or between spheroidal masses of lava 

 isolated by jointing, or else forming a more or less rectangular 

 network around brecciated fragments ; while, very rarely, a 

 relatively large mass of chert is found occupying the centre of a 

 -spheroid. 



A careful examination of the chert-masses described above leads 

 .us to the conclusion that they are all the product of deposition 



