C. A. Cotton— Block Mountains in JVevj Zealand. 267 



and other rivers is perhaps an example (Speight, 1908).^ It is 

 equally probable that this dissection has been the result of a 

 disturbance of the nicely balanced proportion of water to waste 

 brought about by some climatic change. 



Dissection may be caused at a much earlier stage of the cycle 

 by coastal retrogradation or by regional uplift. A good exam- 

 ple of deep dissection of piedmont plains occurs in an aggraded 

 tectonic depression which extends inland in a southwesterly 

 direction along the base of the Seaward Kaikoura Eange and 

 is followed by the coach road from Kaikoura to Waiau. It 

 has been described by Park (1911) as the Waiau "Glacial" 

 Valley. The streams which supplied the alluvium forming the 

 floor of the depression descend from the mountain range, some 

 of them uniting and reaching tlie sea as the Kahautara River, 

 which leaves the depression at its northeastern end, and others 

 uniting and flowing inland to join the Conway Eiver, Owing 

 to recent uplift the streams are now all deeply entrencheS 

 below the aggraded surface which is being rapidly destroyed 

 by the headward erosion of insequent ravines. 



Paet II. The Block Mountains of Central Otago. 

 1. Historical Sketch. 



The origin of the relief of Central Otago has been studied 

 by various writers, and various theories of origin have resulted. 

 Hector (1862, 1869, 1881, 1890) considered the structural fea- 

 tures as the result of normal erosion affected by later regional 

 earth movements. One of Hector's publications (1870) includes 

 an indefinite statement assigning a tectonic origin to the major 

 topographic features. Beal (1871) ascribed the smooth ridges 

 and hillsides to the work of ice and the depressions to stream 

 erosion. Hutton (1875) also believed that the rock-bound 

 depressions of Central Otago, " old lake basins," had been 

 excavated by ice. McKay (1881, 1881^) recognized the oro- 

 genic movements to which the present relief is due and formu- 

 lated a hypothesis which agrees in some essentials with the 

 views presented in this paper. In 1897 McKay recognized a 

 number of great faults in this region, and called attention to 

 the importance of these movements in determining relief. He 

 apparently did not recognize the evidence of tectonic origin in 

 the forms of the mountains and described the depressions as 

 ^' lake basins " and the higher fluviatile gravels as *' lake ter- 

 races." 



Park in 1890 and Gordon in 1893 noted the high inclination 

 •of some of the beds of the covering strata and appear to have 



* In a recent publication, Speight (1911) ascribes the building of the Can- 

 terbury Plains to a postglacial pluvial period and the deep incision of the 

 rivers below the plains surface to a later period of dry climate. 



