C. A. Cotton — Block Mountains in Bew Zealand, 269 



northeast, folded, unaltered or but little altered, and more 

 resistant sedimentary rocks form the nndermass. The transi- 

 tion from typical greywacke to typical schist is in some places 

 quite sharp. Such junctions in*^ Otago are, perhaps without 

 exception, fault junctions. Along the boundary between the 

 main schist area and the main greywacke area the two types of 

 undermass may be distinguished at a distance of several miles 

 by the details of the relief forms developed on them, and the 



Fig. 11. 



Fig. 11. Geologic sketcli map of the block mountains associated "with 

 Central Otago chain of depressions. (Boundaries after McKay, with slight 

 modifications.) The areas in which schist undermass rocks reach the surface 

 are marked by waved north-south lines, the areas of greywacke (unaltered or 

 little altered) by straight north-south lines, and those in which the overmass 

 forms the surface, or is thinly covered by alluvium, by straight east-west 

 lines. Volcanic rocks of the overmass are shown in black. 



presence is thus indicated of a mosaic of blocks separated by a 

 system or systems of relatively ancient faults to which the 

 present relief is largely or wholly indifferent. Some of the 

 blocks of the mosaic are too small to be shown on the small- 

 scale maps hitherto published. 



The relief due to movements on these ancient fault lines 

 (together with that resulting from earlier folding) probably 



