C. A, Cotton — Bloch Mountains in New Zealand. 271 



To the writer's mind conclusive evidence as to the former 

 wide extension^ of an overmass is afforded by the occasional 

 preservation of small outliers of the cover on the upland pla 

 teaus; bj the wide distribution of the " sarsen stones" (fig. 12) 

 dei'ived from the cemented quartz grit; and by the manner in 

 which planed surfaces of the older rocks emerge from under 

 beveled clay and brown coal strata, as well as quartz grits, 

 with the same inclination. 



Fig. 12. 



^tlJP^^^ 











^^__ 







WKSL 



g^^^^^*^ 



^ 





w^ 





r. ..-.«»^'i 



m^r^^m 







~ " '"''^^■HBH 



m 



!•;?,*?<- 





• .. 



1 ^ 



Fig. 12. " Sarsen stones" on the back slopes of the Rough Ridge block. 



3. Major Tectonic Features. 



As in most parts of New Zealand, the larger features in 

 Otago w^ith the exception of the volcanic massif of the Dune- 

 din district are undoubtedly of tectonic origin. The positive 

 forms fall under the head of block mountains of simple or 

 moderately complex types, and in the Central and northeastcn 

 district more than one of the types of block structure recog- 

 nized by Gilbert (1874) in the ranges of the Great Basin are 

 distinguishable. These initial forms have been also sculptured 

 in detail by erosion. 



The area is characterized by uplifts of relatively simple 

 types — uplifted masses either tilted or bounded on both sides by 

 faults forming a set of elongated blocks with a definite south- 

 west and northeast orientation and enclosing elongated depres- 



