502 NEW ZEALAND SOUND (AND LAKE) BASINS, 



ii. South-Western New Zealand. 



(a) An incomplete plain of erosion was induced, by subaerial 

 agencies, in the igneous, sedimentary and crystalline schistose 

 complex. Huge "relict" mountains point to the existence of a 

 former higher plain. 



(b) An enormous differential movement closed this cycle of 

 erosion. Great faultings and flexings appear to have accompanied 

 the elevation. At Preservation Inlet a plateau some 1500 feet 

 high is seen, while apparently the same elevated plain is nearly 

 6000 feet in height* a little farther north. 



(c) Streams acted on this warped mass so as to produce a series 

 of graded valleys. 



(d) Glacial conditions supervening, the old graded water 

 channels were lowered so as to become adjusted to the new and 

 heavier burdens imposed upon them. In this way spurs were 

 removed, valley walls were straightened, hanging valleys were 

 produced, and huge basins were excavated in the valley floors 

 almost 2000 feetf below sea-level. 



THESIS. 



Streams, of whatsoever material composed, and in plateaus how- 

 ever high, attempt an early and decided approximation to main 

 base-level. At a certain stage of erosion a grade occurs along 

 which the strongest floods only obtaining in the particular area 

 under consideration can effect even slight corrasion of the channel 

 bases. Henceforth lateral corrasion gains the ascendancy over 

 vertical work. 



This stream slope may be called the transitional grade. 



In areas of homogeneous material the transitional grades, for 

 streams of varying strength, could be worked out from the 



* E. C. Andrews, (h) figs. 1, 2 and 3. See also J. M. Bell. 

 + As will be shown in this brief note, these sound and lake basins could 

 have been predicted on the assumption of an ice-flood by analogy with the 

 observed work of ordinary streams and sea-waves in respectively excavating 

 basins and cutting platforms below base-level. 



