Speight. — Geology of the West Coast Sounds. 259 



Petrological Notes. 



The remainder of this paper consists of notes on the petrology of the 

 region. These tend to show that the rocks are in all probabihty not truly 

 Archiiean, but are metamorphosed igneous rocks, with perhaps occasional 

 metamorphosed sedimentaries. This conclusion is based on the following 

 evidence : — 



(1.) The rocks never appear to exhibit that profound metamorphism 

 which characterizes most Archaean rocks. 



(2.) Frequently the only sign of metamorphism is the presence of strain 

 and cataclastic effects : gradations in these can be traced from rocks practi- 

 cally without them to those which exhibit them to a marked degree. 



(3.) The rocks do not show the effects of heat on their mineialogical 

 character as they would if they were truly Archsean and had experienced 

 subcrustal changes. They belong to the upper or middle zone of Gruben- 

 mann. 



(4.) Rutile is a prominent constituent of the rocks, and this suggests 

 that some may be altered sedimentaries. Mica-schists, however, are very 

 seldom met with. 



(5.) The marbles occurring at Milford and elsewhere seem to be the 

 result of alterations in igneous rocks (see Marshall), and are not due to 

 change in detrital or organic hmestone. 



It will be seen that the rocks are generally of somewhat acid character, 

 and consist of true gneisses and diorite gneisses, with oUgoclase as the 

 dominant feldspar. Quartz and epidote are prominent constituents, 

 titanite and rutile minor ones, the two latter being occasionally derived 

 from ilmenite. The ferro-magnesian minerals are chiefly hornblende and 

 biotite, although hypersthene and augite occur freely at times ; garnets are 

 very common. 



Amphibolites are of frequent occurrence, and perhaps are basic segrega- 

 tions from the hornblende gneisses, which may represent metamorphosed 

 diabases. In the northern part of the area peridotites and aUied and 

 associated rocks are strongly developed. 



Preservation Inlet. '' 



Specimens were collected at^Kisbee Bay, on the south-east side of the 

 inlet ; some from boulders on the beach. 



Diorite Gneiss (K 1). — This is a distinctly foUated rock, grey in colour. 

 Under the microscope it appears composed of tolerably even-grained ele- 

 ments, consisting of much plagioclase (andesine), a little quartz, greenish- 

 brown hornblende, biotite, grains of ilmenite, occasional titanite and epi- 

 dote, frequent needles of apatite, and a few zircons. 



Diorite (K 2). — A dark-grey rock formed chiefly of hornblende, showing 

 cleavage-surfaces plainly. In section it shows much hornblende in large 

 green crystals and plates exhibiting fibrous structure. The feldspar (ohgo- 

 clase-andesine) is in smaller proportion ; a small amount of quartz is 

 present ; biotite occurs in laths, epidote in grains and aggregates derived 

 from hornblende. There appear to be intergrowths of hornblende with 

 mica ; ilmenite is common in grains. 



Granite. — Granites of various degrees of coarseness are met with, the 

 coarser types with pink feldspar crystals ; some of the finer rock types are 

 pinkish and reddish as a whole. The Coarse-grained ones contain both 

 9*— Trans. 



