CKYSTALLINE SCHISTS INTO IGNEOUS EOCKS IN CO. GALWAY. 519 



places finds its way along the joints, forming a cementing matrix. 

 The mixed rocks thus present a superficial resemblance to a con- 

 glomerate. It appears from this section that the diorite is intrusive 

 in the gneiss, and the granite in the diorite. It would also seem 

 as if the diorite had consolidated and acquired a jointed structure 

 previous to the introduction of the granite. How this ground affords 

 evidence of a passage from granite into schist, I am unable to 

 understand. 



Ground south-east of Glenddlough. 



The singular phenomena I am about to describe occur at the 

 eastern end of a long band of " hornblende-rock," which runs in an 

 east and west direction for a mile and a half. We here see all the 

 steps of the process by which igneous rocks have been converted 

 into a pseudo-conglomerate. 



The prevailing rock is diorite, with a very distinct jointing. On 

 the weathered surfaces the material along the joints has yielded to 

 degrading influences, so that the blocks between stand out in relief. 

 These joint-blocks have a diameter varying between a few inches 

 and perhaps two feet. In shape they are sometimes roughly oval or 

 ovate, but frequently they are partially angular or subangular. 

 Some of them are represented in figs. 1-3. 



There are in this locality several outcropping masses, some of 

 which consist of unbroken diorite. In others, the following appear- 

 ance is observed. For some yards, we pass the jointed diorite; 

 then we see a gradual coming in of the granite. Thin veins find 

 their way along the joints, in one place coming to an end against a 

 joint-block (fig. 1), and in another, where the joints narrow, termi- 



Fig. 1. — Section of Granite in Jointed Diorite. 



nating between adjacent blocks. Wot far off we see veins creeping 

 along each side of a block, but failing to force their way entirely 

 round (fig. 2) ; while close at hand the granite has succeeded in 

 entirely isolating the blocks from the main mass, so that diorite is 

 immersed in granite. It is therefore clear that these pseudo-con- 

 glomerates are merely agglomerations of -joint-blocks imbedded in a 



