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PKOF. T. G. BONNEY 02T THE 



conglomerate consist, as may be seen with the unaided eye, of 

 various kinds of rocks ; some have evidently been derived from more 

 than one species of holocrystalline rock, others from fine-grained 

 quartzose clastic rocks. In the sMes which I have examined, 6 in 

 number, I recognize the following : — granitoid rock 3 varieties, mica- 

 schist 1, quartz-schist 4, quartzite 2, halleflinta ? 2. 



Of the granitoid rocks the coarsest (a pebble about 3" diameter) 

 consists of quartz, felspar, and mica ; the felspar (chiefly orthoclase 

 with some plagioclase) is in fair perservation, but the crystals are 

 often broken across, slightly displaced, and at the edge have a some- 

 what crushed appearance. The quartz occurs in " nests of grains," 

 and as chalcedonic quartz in cracks in the felspar &c. ; the mica, of a 

 rich brown colour, but becoming greenish by alteration, together 

 with a little colourless mica, also occurs in nests of flakes about 

 •01" long. The rock appears to me to have undergone considerable 

 mechanical disturbance, which has cracked the felspar crystals and 

 the original quartz grains, and has crushed the mica fl akes, afi^ecting 

 especially the latter two ; and that then a certain amount of re- 

 crystallization and recementation has taken place. This, however, 

 has not produced any definite orientation in the fragments. It has 

 made it difficult to pronounce as to the true nature of the original 

 rock, but I incline to regard it as a granite rather than a gneiss. 



Another specimen consists of quartz, of rather decomposed felspar 

 (2 species) and a very little dull oHve-coloured mica. Here also I 

 suspect some mechanical modification of the original rock, so that it is 

 hard to say whether it is from a vein-granite or one of those granitoid 

 hands wluch we meet sometimes among rocks apparently not of 

 igneous origin. I incline, however, to the former view. 



The quartz-schists are exceedingly fine-grained rocks containing a 

 fair proportion of brown mica. The quartz grains and the mica 

 flakes do not as a rule exceed about '001". One has rather more 

 mica, and in it the materials are more parallel in arrangement than 

 in the other. The mica- schist is a little coarser and has more mica 

 than quartz. It is a brown mica more or less changed to green, the 

 structure being moderately fohated. The quartzites are coarser 

 rocks, the grains being near -01" in diameter ; they call for no 

 special remark beyond the fact that the quartz grains are rather 

 full of cavities containing small bubbles, and there is here and 

 there a flake of a green mineral, chlorite or altered biotite. I 

 believe these to be true quartzites, but two or three smaller frag- 

 ments more resemble a vein-quartz. The rock to which I have given 

 the vague name halleflinta has a ground-mass consisting apparently 

 almost whoUy of very minute granules of quartz of somewhat chal- 

 cedonic aspect, associated with still more minute microhths of brown 

 mica ; in this are occasional larger quartz grains, not seldom in 

 aggregates of four or five, nests of flakes of brown mica, and felspar 

 crystals, whole or broken. The general aspect of this rock recalls 

 to my mind those halleflintas of TrefiPgarn and Eoche Castle, for 

 long so great a puzzle, and it is possible that, like some, at least, of 

 these, we may have before us here old and altered volcanic glasses. 



