112 MR. GARDIXER AXD PROF. REYNOLDS OX THE [June 1 0. 1 4, 



Tarannon age of these beds. Similar grey flags have been observed 

 to overlie the Purple Sandy Shales at several points along the line 

 of outcrop eastwards, and they probably form a continuous band ; 

 but we have not sufficient evidence to show them on the map 

 (PI. XVII), in which they are coloured with the Doon Pock Grits. 



(6) The Doon Rock Grits (Wenlock). — These massive 

 grits occupy the whole of the southern part of the map. In 

 the Kilbride area they were proved by the contained graptolites to 

 be of Wenlock a°;e. In the Lousrh Xafooev area obscure traces of 

 graptolites have been found in the western part of Glentrague, but 

 these specimens, which did not admit of identification, were the 

 only fossils found in these grits. 



V. Field-Relatioxs or the Intrusive Igneous Rocks. 



(a) The Felsites. 



No masses of felsite occur, comparable in size with those of the 

 Tourmakeady, Glensaul, and Kilbride areas, and the rocks with 

 conspicuous well- terminated quartz-crystals, so characteristic of the 

 large intrusive masses of these areas, are almost completely absent. 



As in the Kilbride area, no felsite intrusions penetrate the 

 Silurian rocks, and throughout the whole area, except near Curragh- 

 revagh hamlet, and on the hillside two-thirds of a mile away to the 

 south, the felsites are confined to the Arenig rocks. On the hillside 

 west of the hamlet, however, outside the boundary of our map, a 

 felsite-sill occurs in the IVhveelrea Grits ; while a second intrusion 

 follows the boundarv between the Arenig and Llandeilo rocks on 

 the left bank of the Curraghrevagh stream ; and a third occurs 

 along the northern face of the ridge extending westwards from 

 near Benbeg, separating the Llandeilo grits from the bostonite-sill 

 at the base of the Silurian. These intrusions are clearly of post- 

 Llandeilo age. We believe, too, that the big intrusion south of 

 Curraghrevagh hamlet is of post-Silurian age, as it is unaffected 

 by a fault which shifts the Silurian deposits. This last-mentioned 

 felsite-mass is the largest in the area, the next largest occurring 

 about 2| miles awaj^ to the east, on the southern slope of Two- 

 Stream Valley. About eighteen other intrusions of felsite, none 

 of them of any great size, have been found penetrating the spilite. 



(b) The Labradorite-Porphyrite. 



This rock occurs associated with bostonite, forming intrusions 

 along the line of unconformity between the Silurian and the Arenig 

 rocks. Only two intrusions were found. One, half a mile east of 

 Bencorragh, is about 400 yards long, and occurs between the 

 bostonite and the spilite. The other, about half a mile west-south- 

 west of the former, seems to cut across the bostonite, so as to appear 

 at its western end between the Silurian rocks and the bostonite, 

 and at its eastern end between the Arenig spilite and the bostonite. 

 'This intrusion has a surface-lenffth of about 250 yards. 



