124 Proceedings of the Royal Irish Academy. 



In structure elvanytes vary ; some are finely crystalline, so as to be 

 nearly compact, wliile others are granular or granitoid, the latter gra- 

 duating into typical granite. Elvanyte graduating into granite is -well 

 exemplified in the neighbourhood of Kylemore. Here, south and south- 

 west of Bengooria or Diamond Hill, are protrusions, in part scarcely 

 distinguishable from tjrpical granite, nevertheless, in all of it blebs or 

 crystals of quartz that were developed before the other rock consti- 

 tuents can be detected, more or less, while toward the margins of the 

 masses the rock is a typical granitoid-elvanyte. Moreover, from the 

 tracts extend numerous dykes, some being large and others small ; all 

 the former are more or less granitoid, while the latter are finely crys- 

 talline or nearly compact, some apparently merging into quartzitic-f el- 

 stone. Part of the rock in mass, although granitoid, has the typical 

 weathering of elvanyte, which seems due to all the quartz and felspar 

 not being crystallized out, parts of these remaining undeveloped ; and 

 from this peculiar weathering the Cornish name seems to be derived 

 (el, oil rock, ban or van white), as the white smooth crust has a marked 

 contrast when compared with the rough weathering of granite. 



Some rocks like elvanyte are gTieissoid. This stracture may possibly 

 be due to metamorphism ; as in the neighbourhood of Galway, in one 

 or two instances it has been proved that some of the elvanjrte is older 

 than some of the typical granite, but as a general rule the elvanytes 

 are newer ; and in the country north of Elillary Harbour, where the 

 rocks are only slightly altered, there are large dykes of foliated 

 elvanyte ; moreover, they were only observed in the neighbourhood of 

 protrusions of granite, and may possibly be connected with them.* 



My fi'iend and colleague, R. Gr. Symes, F. R. G. S. I., &c., seems 

 to have been, one of the first who pointed out the graduation of granite 

 through elvanyte into felstone. While examining the rocks adjoining 

 the north shore of Galway bay, I suspected such must be the case, 

 and mentioned my opinion in the Geological Survey Memoirs. Since 

 then I have seen the gradation in variou.s localities. 



Granite. — Of tyj^ical granite the principal varieties in composition 

 will be found in the following list. There are others, some being very' 

 remarkable, not only in composition, but also in structure ; however, 

 they are only varieties of the rocks enumerated. 



Typical Granites. 



-n • T 1 • -J. ( Metamorphic (Galwav-type-granite). 



Jiasic oligoclasic-gi'anite \ ^ , ■ r\ t. " -i. \ 

 ° '^ ( Intinisive Omey-type-granite). 



Highly siliceous ortholasic- ( Metamorphic. 



granite. ( Intrusive (Oughterard-type-granite). 



* The country between these dykes and the granitic masses is covered with 

 drift. It appears remarkable that these foliated rocks should only have been found 

 hereabout associated with other granitic dykes. This foliation can scarcely be due 

 to metamorphism, on account of the unaltered condition of the associated rocks. 



