242 Geology of 



point of the North Island. This great mountain chain, broken through 

 by Cook's Straits, falls rather abruptly towards the west, having 

 from the divide, only a breadth of about eight to ten miles. Towards 

 the east it slopes down more gradually, a breadth of 50 miles not 

 being uncom m on. This remarkable chain, of which the geological 

 structure is generally uniform throughout, is only the eastern wing 

 ©f a huge anticlinal arrangement, of which the western portion has 

 either been destroyed, or submerged below the Pacific Ocean. It 

 has thus the same one-sided arrangement, so conspicuous in almost 

 every alpine chain of which the geological structure is known. The 

 axis of this anticlinal consists of granite and other plutonic rocks, 

 which still, in some localities in "Westland, are open to our inspection. 

 This granite area is mostly confined to the northern portion of "West- 

 land between Lake Erunner and the "Waitaha, rising in isolated moun- 

 tains from the West Coast plains, and being generally detached from 

 the Southern Alps, so that it is exceedingly difficult to find any contact 

 between the plutonic rocks and the lowest beds which form the 

 western slopes of the Southern Alps ; a low saddle, if not a valley or 

 broader depression, separating them from each other. 



In the chapter on the Physical Geography of Canterbury, I have 

 referred to Mr E. Dobson's interesting observations that all the principal 

 valleys from the Hurunui in the north to the Makaroa in the south, 

 radiate as it were from a common centre situated about 50 miles 

 to the north of Mount Darwin, or about 40 miles west of Hokitika. 

 It is a remarkable coincidence that the granitic zone, stretching 

 from the south of the "Waitaha round Lake Brunner to the west 

 coast, 20 miles north of the Eiver Grey, forms a segment of a circle 

 round that point. A similar segment of a circle is formed by the 

 eruptive and volcanic zone on the eastern slopes of the Southern Alps 

 round Banks' Peninsula. An examination of the Geological Map of 

 the two provinces, attached to this Report, will show that the different 

 principal formations, according to their age, and the metamorphic 

 action they have been subjected to, follow each other from west to 

 east, while the general sections across the Island show this still more 

 convincingly. Thus, beginning at the western slopes of the Alps, we 

 find invariably, where open to our inspection (the deep gorges of 

 the rivers, generally offering us clear sections) that the lowest 

 beds consist of gneiss granites in many varieties of composition 

 and texture. Sometimes they appear in hand specimens, and even in 

 small exposed sections as true granites, but invariably when examining 

 these sections over a larger space, we observe that the rock always 



