C. A. Cotton — Block Mountains in New Zealand. 273 



tions is northwesterly; but still farther to the northeast the 

 first-mentioned system again makes its appearance with perhaps 

 a more northerly trend. The northeasterly trending system 

 of late uplifts dne to dislocations and folds is widespread in 

 ^ew Zealand, while the northwesterly system seems practically 

 confined to Otago, making its appearance again to the south- 

 west of the schist area of Central Otago.^ The dislocations of 

 the two systems do not, as a rule, occur together so as to define 

 a regular rectilinear mosaic, but the blocks within tlie area 

 traversed by the dislocations of each system are elongated like 

 anticlinal and synclinal folds. 



Jt is noticeable that while the block boundaries along the 

 great northwest and southeast scarp that forms the boundary 

 between the depressions and the northern highland coincide 

 more or less exactly with the lines of junction of greywacke 

 and schist areas of the undermass, the metamorphics, which 

 presumably were originally the more deep-seated rocks, occupy 

 the downthrown side. That is to say, the dislocations have 

 followed the lines of more ancient faults of even greater throw, 

 but have displaced the crustal blocks in the reverse direction. 



The Central Otago System. — Confining our attention to the 

 blocks somewhat directly connected with the Central Otago 

 chain of depressions, we find that the most westerly of these — 

 the Manuherikia depression — is bounded on the northwest by 

 a highland block, the Diinstan Mountains, with an average 

 height on the crest of 5,000 feet, or 4,000 feet above the floor 

 of the Manuherikia depression. The even crest of the block 

 indicates that its upper surface is fiat, and any cover that for- 

 merly lay on the planed surface of the undermass has been 

 stripped from it. The southeastward slope from the crest to 

 the depression is a fault scarp, probably not of the simplest type. 



The fioor of the Manuherikia depression (fig. 14) has an 

 average height of about 1,000 feet above sea-level. It is about 

 40 miles long and 8 miles wide. It contains a great thickness 

 of the overmass, the beds of which are cut into terraces and 

 dissected into residual hills, a relief that reaches a height of 

 about 600 feet. The overmass is much obscured by a veneer 

 of postdeformational alluvium. 



The depression is bounded on the southeastern side by a 

 narrow, elongated upland block 3 or 4 miles wide, which a 

 transverse stream divides into two portions. The southwest- 

 ern portion is called the Raggedy Eange and the northeastern, 

 Blackstone Hill. The whole may be termed the Raggedy- 

 Blackstone block. Its somewhat undulating crest line is gener- 

 ally about 2,000 feet above sea-level, but rises to 3,200 feet in 



*In a recent paper, Speight (1916) ascribes the courses of some of the 

 rivers of Canterbury to dislocations with a northwesterly trend. 



