KiLROE — Silurian and Metanwrphic Hocks. 



159 



While the rocks of Croagh Patrick were believed to be of the same 

 group and general age as those at AYestport and north of the Clew Bay, 

 it was easy to dismiss the question of differences in lith ©logical 

 characters between the highly metamorphosed grits and black slate, 

 seen south-east of the town — the counterparts of those north-west 

 of Castlebar — and the rocks forming the range. The question, how- 

 ever, towards the close of the somewhat hurried revision, was perceived 

 to be of so important a nature, involving the age of the great 

 metamorphic series, that it was allowed to lie outstanding until it 

 could be satisfactorily decided. It presents the following features, 

 viz. : — 



1. The great conglomerate of Croagh Patrick is not traceable 

 further eastward than Eelclare, three miles from Westport, on the 

 south-west, where it appears in striking developement. 



2. The quartzite of the range may be followed eastward almost to 

 the Carboniferous boundary, a mile and a half south-east of the town, 

 where it vanishes. 



3. The sericite schist on the south of the range seems continuous 

 around the end, with the similiar silky phyllites which skirt the 

 quartzite on its south side here, as far perhaps as Eelclare, where 

 much broken ground suggests a transverse dislocation of the strata. 



4. The (/reen argillaceous grits at Eelclare have the aspect of 

 Wenlock strata rather than that of the greenish-gray grits associated 

 with the coarse conglomeratic grits and black slate at Westport, and 

 along the shore by Leckanvy beyond Murrisk. 



5. A distinct line may be approximately traced upon the ground 

 between the silky phyllites and green grits, above mentioned, and the 

 coarse grits and black slate near Westport ; and this line seems 

 continuable westward to separate the rocks of the ridge from those 

 nearer to the sea at its foot, though the persistent band of serpentine 

 which invades the two sets of rocks greatly obscures the geological 



following in apparently unbroken succession upward those along the coast north- 

 west of Louisburgh, which, in my opinion, are of Ludlow Age, then it is probable 

 that the overfolding and metamorphism of the rocks at Croagh Patrick took place 

 in Old Red Sandstone times. A provisional boundary is drawn on the map 

 between the Old Head rocks, which are largely conglomeratic, and those south- 

 westward of that point, which consist of red shale and shaley sandstone. 



