MoROAX. — Oil tht Struci lire of the Southern A/j>i<. 277 



Hill nortlivvurd,''' is seen at Lake Kanieri, and forms a considerable area east 

 and south-east of Ross. Greenland rocks appear near Lake Mapourika, 

 and probably have some development farther south. The breaks in the 

 buttress are attributed by the writer to down-faulting, which also is thought 

 since Miocene times to have caused the disappearance of an ancient land- 

 mass to the seaward of the present coast-line (3, pp. 26-28). 



Suess distinguishes two types of overthrust mountain-ranges — the 

 Atlantic, with its outer or overthrust face directed away from the nearest 

 ocean ; and the Pacific type, with its outer face directed towards the nearest 

 ocean. As judged by these definitions, the Southern Alps, though of the 

 Pacific type with respect to the Tasman Sea, are of the Atlantic type with 

 respect to the South Pacific Ocean. This has already been indicated by 

 Marshall (11, p. 445). 



If, as has been assumed throughout this note, the folding of the Green- 

 land rocks from north-west to south-east is older than the folding of the 

 Arahura or alpine rocks from north-east to south-west, then in the alpine 

 region the former folding has been superimposed on the latter. Confirm- 

 ation of this view is afforded by field evidence. According to observations 

 made by Mr. E. Dobson many years ago, the average strike of the strata 

 forming the Southern Alps is N. 22° E., whilst the trend of the range itself 

 is N. 55° E. (1, p. 485). More recently the New Zealand Geological Survev 

 has noted considerable irregularities in the strikes of the alpine rocks in North 

 AVestland (8, p. 42 ; 10, p. 78). These irregularities increase from the in- 

 tensely folded western schists in which the supposed older folding has been 

 almost obliterated towards the main divide, and are very marked on the 

 eastern, or Canterbury, side. Practically all the irregular strikes, except one 

 or two that are nearly east-and-west, fall in the N.E.-N.W. quadrant, and 

 are therefore such as might be expected to result from a folding-force acting 

 from the south-east on strata with an original north-Avest to south-east 

 strike. 



Similar irregularities in strike are very apparent in north-west Nelson 

 in rocks of the Aorere series (9, p. 34). It is here suggested that a similar 

 cause to that indicated above may be assigned for the strike-irregularities 

 in this area and in other parts of New Zealand — for example, the Wha- 

 ngaroa Subdivision (Bull. No. 8, N.Z. Geol. Survey, p. 42). 



This note refers mainly to that part of the Southern Alps with which 

 the writer is acquainted — namely, from the Otira district for about a hundred 

 miles southward. Thus the Southern Alps as they pass north-eastward 

 through Nelson to the shores of Cook Strait, the interesting central knot of 

 Mount Cook, and the comparatively unknown southern portion of the range 

 are not discussed. Before an authoritative opinion concerning the structure 

 of the whole range can be given, a detailed geological survey of practically 

 its entire length, and more especially of the district south of Mount Aspiring, 

 where the Alps begin to lose their identity in the mountain complex of 

 western Otago, must be undertaken. 



In conclusion, it may be said that a full and correct statement of the 

 structure and history of the Southern Alps will be of great importance in 

 aiding the solution of several problems in New Zealand geology, and possibly 

 of still greater value in connection with the elucidation of the wonderful 

 but baffling geophysical problems presented by the Pacific Ocean. 



• * This district, however, is outside the scope of the present note. See last para- 

 graph but one. 



