14 



PEOF. T. G. BONNEY ON THE HOENBLENDIC AND OTHEE 



microliths of haematite and magnetite) an alteration-product from 

 it ; the third, which gives beautiful tints with crossing Nicols, rather 

 resembles paragonite, and is no doubt one of the hydrous soda- or 

 potash-micas. An earthy-looking granular felspathic constituent is 

 occasionally present, as well as several small garnets. These are 

 almost colourless, but often rather crowded with dirty-looking 

 enclosures, and sometimes decomposed ; a little kyanite (?) occurs. 



(8) The lustrous greenish schist, at Porthalla, associated with 

 the granitoid band (p. 8), consists mainly of a colourless mica, gene- 

 rally similar to that just described, with a fair amount of a green 

 mineral, most of which resembles a mica, or possibly a chlorite, more 

 than a hornblende. Quartz, sometimes certainly interstitial, is pre- 

 sent in fair quantity, containing occasionally minute enclosures of 

 the nature of which it is difficult to be certain. We note also some 

 ferrite and impure epidote, sometimes in grains about *01 inch in 

 diameter. 



(9) Compact-looking schist, not far trom the last (p. 8). This 

 consists of films and belonites of green mica or hornblende with 

 quartz, the last generally clear, occasionally with filmy pale brown 

 microlithic enclosures : scales of haematite and, perhaps, some very 

 small garnets are also present, with one or two grains which may 

 be zircon ; transverse cracks with infiltrations, as described above. 



(10) The granitoid rock near the fault, Porthalla (p. 8). The 

 slide consists of quartz, felspar, white mica, tourmaline, chlorite, with 

 iron peroxide. The quartz frequently occurs in irregular patches of 

 aggregated granules of variable size as in a quartzite ; they contain 

 microlithic enclosures of extreme smallness, often much less than 

 •001 inch in diameter, many being cavities apparently empty. The 

 felspar, often much decomposed, occurs sometimes in grains of very 

 irregular outline up to about \3" diameter ; orthoclase and oligo- 

 clase (?) are present. Of the tourmaline, which is not common, there 

 are one or two crystals about the above size, the rest being micro- 

 lithic. I note also a little cluster of garnets. The rock has 

 evidently been crushed, which obliges one to be cautious in pro- 

 nouncing on its structure ; but I think we may safely regard it as 

 a gneiss, not a vein-granite. 



B. Hornblendic Groujj. 



The hornblende schist, of which I have had several slides prepared 

 representing different varieties, is macroscopically a rock consisting 

 of almost black hornblende, with more or less of a whitish fel- 

 spathic mineral, quartz, and often yellowish epidote, the last some- 

 times occurring abundantly. The crystalline grains usually do 

 not exceed about -05" in diameter. It varies from a massive rock, 

 difficult to distinguish in hand-specimens from a diorite, to one 

 distinctly foliated, finely banded, and obviously of stratified origin, 

 sometimes even showing lenticular and still more minute current- 

 bedding structures. Occasionally there is an approach to a por- 

 phyritic structure, denoted by the presence of eyes or spots of a 



