45 



THE SOUTHERN ALPS. 



The Southern Alps are usually considered to extend from Mount 

 Aspiring (9,975 ft.), west of Lake Wanaka, to about the head of the 

 Grey River, in north Westland. The mountains of western Otago, 

 however, should be included in the alpine system ; and, so far from 

 terminating in north Westland, the range continues north-eastward 

 through Nelson and Marlborough to the southern shore of Cook 

 Strait. North of the Grey River the range is known first as the 

 Spenser Mountains, next as the St. Arnaud Mountains, and then, 

 although still of considerable height, is for many miles without a 

 definite geographical name. 



The mountains of western Otago, with Earnslaw (9,200 ft.) and 

 Tutoko (9,042 ft.) as their highest points, form a congeries of ranges 

 separated by deep valleys, some of which are occupied by lakes, and 

 others, the fiords, by the waters of the sea. They seem to owe their 

 present height to simple uplift rather than to the operation of folding 

 forces, and are therefore to be regarded as belonging to a block- 

 mountain system. 



From Mount Aspiring northwards the Southern Alps appear on 

 the western side as a definite, deeply dissected, but unbroken range, 

 dropping steeply to the moraine-covered lowlands of Westland. On 

 the eastern side, broken into somewhat irregular ranges by the river- 

 valleys, &c., they extend many miles towards the Canterbury Plain. 

 Greywackes and argillites of Trias-Jura age, strongly but irregularly 

 folded and clearly much faulted, form almost the whole of the Canter- 

 bury mountains. West of the main divide these rocks gradually pass 

 into schistose greywackes and phyllites, and finally into closely folded 

 mica-schists, on the whole striking north-north-east, or somewhat to 

 the west of the trend of the range. On the extreme western margin 

 of the Alps there is some gneiss, which, like the schists, may repre- 

 sent highly metamorphosed sedimentary rocks. Separated from the 

 Alps proper and from one another by deep valleys, several mountains, 

 formed wholly or mainly of granite, overlook the Westland lowlands. 



Hochstetter, Haast, and Hutton explain the Southern Alps as a 

 folded mountain-range, forming a huge geanticlinal, of which only 

 the eastern half has been preserved. The western half, according to 

 Hochstetter, is " buried in the depth of the main " (? downfaulted), 

 or, according to Hutton, has been removed by erosion. The geological 

 studies of recent years show that the western side of the Southern 

 Alps is bounded by a great fault, and that, as it now stands, the 

 range is an uplifted block, tilted slightly south-eastward, and probably 

 somewhat, but not greatly, modified in structure by a compressive 

 force acting from the south-east. The writer thinks that uplift 

 occurred in the Pliocene and perhaps also in early Tertiary times. 

 The folding of the rocks is conceived as belonging mainly to an earlier 

 period, probably the late Jurassic or early Cretaceous. The Spenser 

 and St. Arnaud mountains have the same structure as the Southern 

 Alps, and, as previously indicated, are essentially one and the same 

 range. 



Among the higher alpine peaks are the following : Mount Aspiring 

 (9.975 ft -)' Mount Cook (12,349 ft.), Mount Tasman (11,497 ft.), Mount 



