268 G. H. Kinahan — On Metamorphic Rocks. 



occur in more or less regular protrusions and dykes, and not in the 

 irregular and tortuous intrusions and veins so common to some 

 granite. 



MacCulloch's remarks on this class prove that some at least of 

 them are not typical granites, as he distinctly mentions that all the 

 constituents are not crystallized out. 



The rocks of MacCuUoch's class B, second division of the granite,^ 

 would answer the description for some of the varieties of the horn- 

 blende-rock. These rocks in the first stage are a highly crystalline 

 compact mass, that might perhaps be called Hornblende-aphanyte, or 

 it may be for the most part a crystalline aggregate of amphibole+ 

 felspar, not orthoclase (Diorite), or amphibole+orthoclase (Syenite), 

 or ripidolite, talc or mica may replace more or less the amphibole. 

 In these rocks quartz may be present as an accessory, but eventually 

 it appears as an essential, and they merge into granite. 



In the third division,^ class A is the typical metamorphic granite 

 of the " Galway type," while C, D, and E, are varieties, and class F 

 appears not to be a normal rock. Class B is evidently one of the 

 metamorphosed felstones previously described, in which part of the 

 felsite is not developed into quartz and felspar, a not uncommon 

 rock in parts of West Galway. Of these rocks MacCuUoch makes 

 a similar remark to that in reference to those in his second division, 

 class A, pointing out that all of the constituents may not be crystal- 

 lized out, and a similar remark is applicable to these rocks in West 

 Galway. As a supplement to the granite,^ there is a rock described 

 called WTiitestone, a compound of "mica and compact felspar" (felsite). 

 Under this head apparently are classed two distinct rocks, one being 

 a felstone in the schistose stage of metamorphism, and the other 

 being a felsite-schist, a metamorphosed sedimentary rock; both 

 kinds occur in West Galway. 



In conclusion, it may be pointed out that this author, as he himself 

 allows, did not fully understand the nature of serpentine ; conse- 

 quently he has mixed up together rocks of quite different origins. 

 These rocks, however, and their origin, will be described in forth- 

 coming Memoirs of the Irish branch of the Geological Survey. 



EXPLANATION OF PLATE VII. 



Fig. 1. Diagrammatic sketch, showing flows of Hornblende-rock, interstratified with 

 schist. 



Fig. 2. A junction of Hornblende-rock with schist. 



Fig. 3. Nodular Hornblende-rock graduating upwards into Conglomeritic-schist. 



Fig. 4. Nodular Hornblende-rock graduating at the margin of a flow into Conglome- 

 ritic-schist. 



Fig. 6. Conglomeritic-schist ; showing irregular foliation in the matrix, while in the 

 enclosed blocks (most of them being some one or other variety of Horn- 

 blende-rock) there is a faint foliation developed, which is evidently 

 induced by the grain or structure of the original rocks. 



Fig. 6. Conglomeritic-gneiss changing into Granitoid-gneiss, a linear foliation having 

 been developed both in the enclosed blocks and the matrix, the texture of 

 the former being coarse and of the latter fine. 



Fig. 7. Granitoid-gneiss or Gneissoid-granite, with schistose layers or seams. 



» MacCulloch, p. 237. * MacCulloch, p. 238. ^ MacCuUoch, p. 241. 



