PRECARBONIFEROTTS ROCKS OF CHARNWOOD FOREST. 223 



base crowded with minute plagioclase crystals &c, doubtless the 

 more glassy condition of the same rock. 



Buddon- Wood Dyke. — This dyke crosses the granite pit in nearly 

 an east and west direction (the greater part of the excavation 

 being worked behind it), dipping about 70° to the south, and being 

 about ten feet thick. Above it is often a fissure filled with granite 

 breccia, but the junctions are sometimes close. It is a hard, tough, 

 heavy rock of a dull reddish-grey or purplish colour, with dark green 

 spots, and is minutely crystalline, showing occasional distinct small 

 crystals of plagioclase felspar. In appearance it approaches nearer 

 to some of the duller specimens of the compact syenite of Groby than 

 the other above-mentioned dykes. 



The microscope shows it to consist of altered plagioclase felspar, 

 magnetite, viridite, and the remains of a pyroxenic mineral, not very 

 characteristic, but rather more resembling augite than hornblende ; 

 some of the viridite looks like a pseudomorph after biotite. The 

 rock is probably an altered felspathic basalt rather than a true 

 diorite. 



The Rev. J. H. Timins gives an analysis of this rock (Q. J. G. S, 

 vol. xxiii. p. 364): — 



Silica 51-23 



Alumina '. 18-10 



Oxide of iron 4-41 



Oxide of copper 0*70 



Lime 5-72 



Magnesia 3*13 



Loss on ignition 5-21 



Alkalies and loss 11-50 (alkalies abundant). 



100-00 



Mr. Harrison (' Geology of Leicestershire/ p. 11), who quotes this 

 analysis, refers it to the felsite behind the Mount-Sorrel pit. The 

 appearance of the rock itself negatives this supposition, and the 

 silica percentage of the former places the matter beyond doubt. 

 Mr. Timins did not collect the specimen himself, and. so could give us 

 no further information than what he had printed— " a red felspathic 

 trap three quarters of a mile south of Quorndon." This, however, 

 accurately describes the above locality, and not Mount-Sorrel pit ; 

 and he kindly sent us a fragment of a rock resembling the one he had 

 analyzed (that having been lost), which was much more like this of 

 which we speak. Hence we have no doubt of the identification. 

 This dyke is the one mentioned by Professor Jukes. 



Dyke in Brazil Wood. — The peculiar sharp jointing of this dyke, 

 which is exposed in a little pit on the west side of the granite knoll, 

 distinguishes it at once from that rock, but it is hard to trace owing 

 to the character of the ground. It is a finely crystalline rock of a 

 dull greenish colour, weathering brown, faintly speckled with a 

 greyer tint, and showing a good many ill-defined spots of a some- 

 what decomposed reddish felspar. 



