564 Transactions. 



Alps," has described facts that are point for point repeated 

 time and again in the glacial regions in the south-west of Otago. 

 It is inconceivable to me that earth-movements, sudden or 

 gradual, could account for the many peculiar physiographic a 1 

 features which have been alluded to in the previous pages. 



The general geological structure of the district is indicated 

 in the small sketch-map on p. 566. It is here advisable only 

 to state that the district is one of mica-schist and phyllites, 

 with a dip and strike that varies little throughout the area. 

 Their age is still doubtful, for while Captain Hutton has lately 

 classed them as of Archaean formation, Sir James Hector has 

 classed them as Silurian, and other divergent statements are 

 not wanting. Through this schist there is intruded an igneous 

 mass which outcrops at the Olivine Saddle, as afterwards de- 

 scribed. 



The following rock-types have been distinguished, and their 

 petrographical characters are described : — 



Diorite. — Bryneira Saddle, between Olivine Creek and Lake 

 Alabaster. Hand-specimen medium-grained. Hornblende and 

 feldspar can be distinguished. Section : All the feldspar is 

 completely saussukitised, and the hornblende is uralitic. The 

 exact original nature of this rock can only be guessed at. 



Gabbro. — Cow Saddle. A coarse-grained rock showing de- 

 composed feldspar and large cleavage-surfaces of diallage. In 

 section the diallage is fairly fresh, but the feldspar is completely 

 changed into saussurite. 



Pyroxenite. — Cow Saddle. Cleavage surfaces of diallage nu- 

 merous and conspicuous. The mineral appears to constitute 

 nine-tenths of the rock. In section the spaces between the 

 diallage-grains are small, and are entirely filled with serpen- 

 tine, mingled with which is some pyrite. 



Lherzolite. — Cow Saddle. A pale-yellow rock showing many 

 cleavage surfaces of a pyroxene imbedded in the olivine. Sec- 

 tions show large irregular grains of olivine nearly fresh. Pyrox- 

 ene, both monoclinic and orthorhombic, is present. The former 

 is a very pale-green, and is referred with certainty to diopsicle. 

 The orthorhombie pyroxene is quite colourless, and is certainlv 

 enstatite. In addition there is a fair quantity of a yellow mine- 

 ral with a high index of refraction. It is far more transparent 

 than the chromite of the dunite of Nelson and of Milford Soun ■!. 

 and is probably a chrome picotite. The mineral has not yel 

 been separated for analysis. This description of the rock will 

 be found to agree satisfactorily with the description of rocks 

 from the Red Hill by Professor Ulrich.* In this description, 



* Quart. Jom-n. Geol. Soc, vol. xlvi, 1890, p. 627. 



