C. A. Cotton — Block Mountains in Neio Zealand. 287 



ridges of Table Mountain sandstone in southeastern Cape 

 Colony (Davis, 1906, fig. 6). 



.Details of the Surface on Schist Bloclcs. — The same genei*al 

 tjpe of relief is found on the schist and on the greywacke 

 blocks. The surfaces of the latter are smooth and soil-covered 

 (fig. 24) ; on the former are many residual tors — great castle- 

 like, joint-bounded masses of bare schist (fig. 25). Tors are 

 characteristic of a Central Otago landscape, and they have sug- 

 gested the names given to many of the schist mountains — as, 



Fig. 24. 



Fig. 24. Youthfully dissected stripped surface of a small greywacke 

 block in the larger fault angle between the northern end of the Raggedy- 

 Blackstone block and the scarp of the northern highland. 



Rough Ridge and Raggedy Range. In the humid area towards 

 the coast, tors are not found ; they are largest and most abun- 

 dant in the most arid districts, a gradual transition being trace- 

 able from the humid to the arid area. The development of the 

 schist tors is, therefore, controlled by climate. They are found 

 on both horizontal and sloping block surfaces, and their form 

 is most characteristic and regular where the schist lies nearly 

 horizontally. 



The uneven resistance of the schist to erosion .is probably 

 not due to differences in composition, as suggested by Rickard 

 (1893, p. 419). Finlayson (1908, p. 73) and Park (1908, p. 12) 

 have noted that the tors are bounded by joint planes. It 



