Wild. — Geology of the Bluff. 



32y 



down the nearer they are to the plutonic mass; (2) the decomposition 

 of the feldspar phenocrysts corresponds to an increase in the amount of 

 hornblende in the rock. 



These facts will be made use of when we discuss the origin of rhe 

 hornblende schists (p. 3*34). 



Chemical Composition . — A sample of specimen No. 4, series A, was 

 submitted to chemical analysis, with the result given in the following 

 table. This analysis probably represents the average composition of the 

 schists, though microscopical examination of sections leads one to expect 

 more acid results in the case of the outer members of the series, and 

 more basic results in the case of those neai-er the norite. 



Si0 2 . . 



TiO 



Al 2 6 3 .. 

 Fe 2 3 .. 

 FeO . . 

 MnO . . 

 CaO . . 

 MgO . . 

 K 2 .. 

 Na 2 . . 

 Loss on ignition . 



61-00 



Total 



Specific gravity, 256. 



100-33 



Class II. — Basic Metamorphic Rocks. 

 1. Amphibolite. 



Parallel with the series of hornblende schists just described is a band 

 of coarse hornblende rock. The outcrop commences at a point 330 ft. 

 from the shore-line measured along the line CD on the map, and extends 

 below the level of low water a distance of 27 ft. 



Hand-specimen (specific gravity = 2'94). — A coarse-grained black or 

 dark-green rock. The weathered surface is rough on account of the 

 exposure of large crystals of hornblende. A freshly broken specimen 

 shows the bright cleavage surfaces of the hornblende. The rock appears 

 to be almost wholly crystalline, there being but a small quantity of a 

 dark-coloured matrix. There is no appearance of schistosity. 



Under the Microscope. — The rock contains a very little feldspar in 

 small grains in granular masses of dark hornblende. The rest is horn- 

 blende, a pale watery-green variety, feebly pleochroic, and fibrous in 

 structure, all of which characters identify it as the form known as 

 uralite. Where the fibres of uralite are packed together into large 

 groups it is easy to recognize some of the edges of former crystals of 

 pyroxene, but more commonly the fibres have broken away from the 

 mass, inducing a schistose character. 



That uralitization has taken place in the amphibolite can be proved 

 in a most satisfactory manner. At Green Point several dykes of a 

 diabase, a rock mineralogieally and chemically similar to but less meta- 

 morphic than this amphibolite, are found, striking north-west to south- 

 east. One of the dykes has suffered to a very considerable extent from 

 the effects of weathering. Tn consequence of this, crystals are found to 



