390 Transactions. — Geology. 



boundaries. Twinned repeatedly according to albite and 

 pericline laws, as well as Carlsbad. Lamellae generally broad. 

 Extinction angle in sections perpendicular to 010 bigb in a 

 few instances, proving the mineral to be anorthite olivine 

 with rounded boundaries. Irregular cracks penetrating it, 

 bordered by magnetite, and occasionally serpentine. A few 

 grains of hypersthene showing strong pleochroisrn associated 

 with the olivine. A few scattered grains of magnetite. 



Of the rocks described above, syenites have been men- 

 tioned in the Geological Survey reports as occurring in many 

 distinct localities within the drainage-basin of the lake as in- 

 trusive rocks. The diorites, granites, gneiss, and forellenstem 

 are similar to some of the types classified together by the 

 Survey as crystalline schists. These rocks are particularly 

 characteristic of the Sounds region, though the distribution of 

 the different types has not yet been ascertained in any of the 

 districts where they occur. The porphyrite is a type that 

 has not been recorded within this district by the officers of 

 the Survey. 



From the descriptions given it will be seen, on reference to 

 a geological map, that these rocks must have been derived 

 from various sources. In the "Reports of the New Zealand 

 Geological Survey, 1879-80," p. 129, a map is given illus- 

 trating the results of an examination of the country to the 

 north and w 7 est of Lake Wakatipu by Mr. A. McKay. In this 

 map the nearest outcrop of crystalline schists to the lake is 

 that in the Hollyford Valley. It is stated in this report that 

 the depth of the Hollyford Valley is the cause of the appear- 

 ance of these rocks. The report states that syenites occur as 

 intrusive masses in many places between the Maitai and Te 

 Anau series, and as several junctions of these two series are 

 shown within the present drainage-basin of the lake their 

 presence in the moraine was to be expected. 



The country further to the north and east was examined 

 by Professor Park in 1886-87 (" Geological Survey Reports, 

 1886-87," p. 121). The map accompanying the report shows 

 crystalline schists on the west side of the Humboldt Moun- 

 tains, again outside the present drainage-basin. These are 

 the only notices I can find of these rocks near the lake. 



A specimen of a rock quite similar to the porphyrite was 

 brought me from the Kawarau gravels, and, as this rock is 

 from its nature certain to be local in its occurrence, it must, in 

 the absence of other evidence, be taken as probable that the 

 two rocks come from the same locality. 



These results are of some interest, for the presence of the 

 "crystalline schists" shows that, if the occurrence of these 

 rocks is correctly mapped, the ice of the Wakatipu glacier 

 must have been partly derived from an area now beyond the 



