518 



DE. C. CALLAWAY ON THE ALLEGED CONVEESION OP 



or nearly all traces of foliation which succeeded the stratification " 

 had been obliterated. 



In the " metamorphic sedimentary rocks " are " conglomeritic 

 beds," containing large and small blocks, sometimes sparingly 

 scattered through the mass, but often thickly together." When the 

 blocks are scattered they are considered to be due to a nodular 

 structure in the original rock ; but when numerous, the rock is 

 regarded as " metamorphosed conglomerate." 



Of the numerous varieties of igneous rocks described in the Survey 

 Memoirs, I shall usually be able to confine myself to two, granite 

 and diorite. The granite is either uniform in grain or porphyritic, 

 and either kind may be foliated. The diorite is generally a dark- 

 green coarsely crystalline rock without varietal differences of 

 importance. For the purposes of this paper, it will be unnecessary 

 to notice minute distinctions. 



1. Geneeal Disteibution oe the Igneous Rocks. 



The granite forms an extensive area reaching from the town of 

 Galway all along the northern side of Galway Bay to the open 

 Atlantic, and broadening out towards the west to a width of nearly 

 20 miles. It also appears in irregular intrusions amongst the 

 schistose rocks to the north of the main mass. The most prominent 

 exposures of the diorite are dotted at intervals round the northerly 

 margin of the chief granite mass, either at a little distance from 

 it or in actual contact with it. 



2. The Relations oe the Igneous Rocks to each othee and 



to the Schists. 



Knockseefin. 



This hill lies nearly 4 miles to the south of Oughterard, and 

 close to the margin of the chief granite-mass of the region. This is 

 stated * to be the typical locality for witnessing the passage of 

 granite into schist. 



The ground is covered between the granite and the gneiss of 

 which the hill is chiefly composed. The latter rock is a mica- gneiss 

 of coarse grain, but clearly banded, weathering on strike-surfaces 

 in fine parallel raised lines. The foliation -planes strike to the If.W. 

 Towards the summit, nodules of diorite, lenticular in horizontal 

 section, made their appearance in the gneiss, their longer axes 

 running with the strike. These are apparently the extremities of 

 veins which have been flattened by pressure. 



The diorite-nodules (veins) increase in number towards the top 

 of the peak, and at the very summit the rock is nearly all diorite. 

 Granite here comes in, irregularly penetrating the diorite. The 

 latter displays a sort of nodular jointing, the joint-blocks running 

 in a roughly linear manner to the N.W., while the granite in 



* Kinahan's 'Geology of Ireland,' p. 190. 



