﻿218 PEOF. S. J. SIIAND ON [vol. lxxii, 



The analytical results are tabulated below under tbese numbers: — 







a ) 



(A 0) 





A/1-S7 



RR-QK 



DO yo 



A7-79 



A 1 A 



1 K-RO 

 10 o& 





1 t;-7Q 







± Do 



1 -nj, 

 1 \j-± 





9- Kft 



9.1 Q 

 Z IB 



9-^Q 

 .3 00 





1 -77 



1 »QQ 



v yy 



CaO 



3-73 



3 - 25 



2 - 93 i 



"Mq n 









it r» 



g.no 



O.Qlr 



9-91 







n- ^1 



U Ol 



u Do 



tt r\ 





A- 1 9 



n-i 1 

 u 11 





1 -^9 



I/O 



1 --^A 

 1 00 



P 2 0 5 



0-27 



0-07 



0-11 



S0 3 



none 



none 



none 



s 



U UD 







MnO 



0-05 



0-03 



0-02 



SrO 



trace 



none 



0-03 



BaO 



0-01 



0-05 



o-oi 



CI 



trace 



trace 



trace 



Totals 



99-96 



100-22 



99-84 



Less 0 



0-02 



0-05 







99-94 



100-17 





The analysed specimen of the granite-gneiss is distinctly banded 

 in hand-specimen, the individual bands of alternately light and 

 dark colour being 1 to 2 mm. thick and neither regular nor 

 persistent when examined minutely, yet sufficiently so to give a 

 distinct grain to the rook. Both white and flesh-red felspars are 

 seen, the latter being the larger and tending to produce eyes. 

 Both orthoclase and oligoclase are present, with biotite as the only 

 dark silicate. Grains of apatite are rather abundant, with some 

 ilmenite and titanite, and large irregular patches of quartz make 

 up about a quarter of the rock. The chemical and microscopical 

 characters determine the rock to be essentially a granodiorite; but, 

 as I have already expressed the opinion that the whole mass is a 

 hybrid granite-gneiss the composition of which varies greatly from 

 place to place, there is no need to lay stress on the name. 



The analysed specimens of pseudotachylyte are of my type 2, 

 passing towards 3 — that is to say, they contain abundant horn- 

 blende-needles and magnetite-grains ; but in places, and especially 

 round the larger inclusions, felspar-laths are also prominently 

 developed. 



Comparing the figures for the two kinds of rock, it is evident 

 that they are so nearly identical as positively to exclude the 

 participation of a foreign magma in the production of the pseudo- 

 tachylyte. The greater content of potash, magnesia, and iron in 

 the pseudotachylyte, as compared witli the granite, doubtless arises 



