G. S. Kinahan— On Metamorphic Rocks. 267 



altered into granite. Granites formed by metamorphism from 

 Petrosilex or any other highly silicious felstone will be more or less 

 highly silicious, while those due to Euryte or Whinstone will be 

 more or less basic, containing as essentials oligoclase, amphibole, 

 titanite, ripidolite, and such like minerals. 



From this it would appear that the rocks included in MacCulloch's 

 Granite of the first division under A and B,^ are highly silicious 

 felstone {Petrosilex) in the schistose stage, while the rocks classed 

 under D are partly metamorphosed whinstone.'^ As among the 

 original rocks of Galway, so also among the original Scottish rocks, 

 there were bedded masses of whinstone and euryte graduating 

 into tuff and agglomerate, and these, when metamorphosed, became 

 hornblende-rock (more or less basic according to the nature of the 

 origiual rock), hornblende- schist, and conglomeritic schists. This, 

 however, does not seem to have impressed itself on MacCullooh, 

 who gets over the difficulty by classing some of the hornblende- 

 rocks among the granite, and the rest among the hornblende-schist, 

 although he allows that the rocks are identical ; this will be also 

 seen from his descriptions. Furthermore, while writing of the 

 varieties (& and c) of this rock, he points out their similarity to 

 Plutonic-rocks, which only goes further to prove their metamorphic 

 origin, as such varieties in West Galway only occur among partially 

 metamorphosed sedimentary rocks. 



In his '' second division " of the Granite, MacCulloch is rather 

 obscure, as his group A^ would include both the highly silicious 

 granite and the metamorphosed or granitic-felstones of West Galway. 

 In that country the amorphous felstones at the first become a felsitic 

 mass mixed with mica ; second, a felsitic mass m. which there is more 

 or less mica, felspar, and quartz developed ; till eventually all 

 the minerals are developed, changing it into a true granite. 

 Although MacCulloch's classification is adopted by most geolo- 

 gists and petrologists of the present day, nevertheless, I believe, 

 it is incorrect, as the metamorphosed felstones generally can be found 

 graduating from a felstone through a gneissic-rock into a granite ; 

 moreover, when studied and consequently known, their make, form 

 and character are peculiar, and readily distinguishable from those 

 of the highly silicious granite. The typical highly silicious granite 

 weathers with the rough rugged aspect so characteristic of all 

 typical granites, while the granitic-felstone has a weathering not 

 smooth, like the weathering of felstone, or yet rough, like that of 

 granite, but rather partaking of the nature of both ; it moreover is 

 inclined to form a whitish crust like a felstone. In typical highly 

 silicious granite the rock may graduate from coarse to fine ; but in the 

 granitic-felstone the rock is often thin, very fine or coarse bands striping 

 the rock, like ribbon, differing not only in texture, but usually in 

 colour and composition. These bands apparently follow a structure 

 in the original rock, probably the lines of viscid fusion. Moreover, 

 the outside of large veins and masses may be quite granitic, while 

 the inside portions are very little altered. Furthermore, these rocks 

 1 MacCulloch, p. 234. ^ MacCulloch, p. 235. ^ MacCulloch, p. 236. 



