C. B. Horwood S^ A. Wade — The Old Granites of Africa. 551 



tiny needles, included cMefly in the felspars and biotites. Sometimes 

 small aggregates occur, and these are especially associated with the 

 biotite flakes. Large crystals, giving well-defined hexagonal basal 

 sections (PL XXVII, Fig. 1), are also present. Epidote occurs in quite 

 large grains and aggregates, sometimes forming a fairly large proportion 

 of the section under consideration. It is of the pale lemon-coloured 

 variety, distinctly pleochroic, and possessing strong birefringence. The 

 large size and idiomorphic character of some of the grains give 

 a first impression that the mineral may be primary. It is, however, 

 always closely associated with much altered felspars, and is occasionally 

 seen as small grains enclosed in them. It is therefore much more 

 likely to be a secondary produce. Some colourless grains enclosed in 

 the micas suggest the mineral zoisite, whilst others, exceedingly 

 scarce, had two sets of cleavages at 70° with one another, and 

 extremely weak birefringence. The characters suggest fluor, though 

 on account of the very small size of the grains and the thinness of the 

 section confirmation by chemical tests could not be obtained. The 

 rock is a Biotite Granite, somewhat rich in soda, with much sphene 

 and epidote. 



An analysis of the rock, with a comparison with those of some 

 of the best known British soda granites, and with that of the New 

 Ked Bushveld Granite of the Transvaal, may prove instructive — 



Age. 



I.i Orange Grove Granite, TrausvaaL (Fresh.) .... Pre-Carboniferous. 



II.' Grey Granite of Slieve-na-Glcgh, Carliugfonl . . . Post- Carboniferous. 



III.- Soda Granite, Newry. (Mean of two analyses.) . . . ,, 



IV. 2 Soda Granites of S.E. Ireland. (Mean of nine analyses.) Pre-Carboniferous. 



V.2 Soda Granite, Croghan Kinshela, S.E. Ireland ... ,, 



VI. 3 Bushveld Granite, Eoodepoortje (149), Transvaal. (Fresh.) ,, 



' The Witiimterxraiicl and Associated Beds, by C. B. Horwood, 1905 (Essou and 

 Perkins, Johannesburg), pp. 70-1. 



2 Analyses quoted by Teall, Brit. Petrog., 1888, pp. 310-50. 



3 C. B. Horwood, loc. cit., pp. 70-1. 



