G. A, Cotton — Block Mountains in New Zealand. 275 



Farther south, however, it is complex and relatively wide, two 

 broad splinters descending towards the northeast and formincr 

 offsets on the lowland level between the northeast-trending 

 fault-scarp portions of the boundary line between the Rough 

 Ridge block and the next depression to the east. 



This depression, about 250 square miles in area, includes 

 the Upper Taieri plain and the Maniototo plain— the whole 

 being termed here the Maniototo depression. The lowest part 

 of its floor is about 1,000 feet above the sea; the mean height 

 of the Upper Taieri plain is about 1,200 feet and of the Mani- 



FiG. 15. 



C.O.CoM-on.l'dlS-. 



Fig. 15. The scarp or front face of the Raggedy-Blackstone block (Black- 

 stone Hill portion). 



ototo plain about 1,500 feet. Considerable portions of the sur- 

 face are covered by a layer of postdeformational alluvium, but 

 at many points the beds of the overmass appear, among which 

 on the eastern side are sheets of basalt. At the northwestern 

 side low islands of the undermass emerge througii the cover, 

 the largest being almost continuous with the first splinter from 

 the Rough Ridge block. To the south, as in the neighboring 

 Ida Yalley depression, the stripped surface of the undermass 

 emerges, aud the line of division between the depression and 

 the southern highland plateau is not simple. 



A high block southeast of the Maniototo depression forms 

 the Rock and Pillar Range, about 8 miles broad. Its western 

 boundary is in part a fault scarp replaced towards the north 

 by a steeply dipping " fold-surface," which passes under a 

 sheet of cover preserved by basalt. The top of the range, 

 presumably a stripped plateau, is gently inclined towards the 

 northwest. The whole drainage of the highland surface is 

 led away in that direction, and profound gorges are cut in the 

 western scarp. In the highest portion of this block, the 

 southeastern edge is about 4,500 feet above the sea, more than 

 3,000 feet above the floor of the depression on the western 

 side and nearly 4,000 feet on the eastern side. At its north- 



