128 MR. GARDINER AND PROF. REYNOLDS ON THE [May 1909, 



The green felsite-mass further gives off, from a point near 

 Gortbunacullin, a long narrow tongue, which stretches north- 

 eastwards through the grits and cherts and can be traced nearly 

 to the western bank of Stream G until cut off by a fault. The total 

 length of this tongue is more than half a mile. 



The brown felsite, which is practically identical with the green, 

 the difference of colour being unimportant, forms a patch with a 

 length of about a third of a mile lying north-west of Shangort, and 

 a smaller patch lying east of the green felsite-mass. Brown felsite 

 of similar character to the above also occurs at various points near 

 Tourmakeady and near Gortanalderg. 



Intrusive masses of felsite, which agree with the main green 

 felsite as regards both colour and the prominence of the pheno- 

 crysts, occur south-west of the district with which this paper deals, 

 only their north-eastern terminations entering it. They form two 

 long narrow tongues, each having a length of over a mile and 

 a width which rarely exceeds 150 yards. The more southerly, 

 commencing near Cappaghduff West, follows the Glensaul river and 

 ends in the Tourmakeady demesne. The more northerly, commencing 

 at a point nearly due west of the termination of the more southerly, 

 extends towards Gortanaldei'g. It is possible that the two may 

 be parts of the same baud shifted by a fault. Neither band makes 

 any prominent surface-feature. 



(/3) The red felsite. — Though the prevalence of a red colour 

 justifies us in referring to this rock as the red felsite, it is not 

 implied that the redness is an invariable characteristic, the rock 

 often locally becoming brown or green. In the bed of Stream B 

 is seen the southernmost outcrop of the great stretch of red felsite 

 which, except for a brief break in Stream F at Gortbunacullin-Farm 

 bridge, extends continuously to Shangort, a distance of 3| miles. 

 For the first three-quarters of a mile, from Stream B to Stream C, 

 the red felsite has an outcrop with a fairly uniform width of about 

 300 yards; but, from Stream C onwards to Stream F, the outcrop 

 becomes very much wider, the maximum width occurring at a point 

 north-west of Drumcoggy Rectory and measuring about 1100 yards. 

 The most remarkable feature about the outcrop is, however, its 

 extraordinarily sinuous character. Along the western margin it 

 repeatedly bends eastward, so that it passes to the oast of successive 

 patches of limestone-breccia ; while along its eastern border its 

 westward bending, so as to pass to the west of patches of grits and 

 cherts, is almost equally noteworthy. South-west of Drumcoggy 

 Rectory one large patch and several smaller patches of grits, cherts, 

 and tuffs are completely surrounded by it. But, while along this 

 lengthy outcrop it is clearly exposed at many points in the 

 neighbourhood, now of the grits and cherts, now of the coarse tuffs, 

 and now of the limestone- breccia, only at one point have we been 

 able to find it actually in contact with any of these rocks. This 

 point is along the south-western border of the triangular area of 



