THE GEOLOGY OF NEW ZEALAND ii 



region were still unreduced, and a great thickness of conglomerate 

 was laid down prior to the formation of the coal-measures, which 

 in turn are succeeded by marine mudstones, the fossils of which 

 contain less than 5 per cent of recent forms. On the other hand, 

 in the southeastern portion of the South Island, the Upper Cre- 

 taceous coal-measures are succeeded by soft mudstones or impure 

 limestones, which Marshall found to contain less than 10 per cent 

 of Recent forms in rather extensive faunas, including also some 

 characteristic early Tertiary genera. In the northeastern part 

 of the South Island a series of marly rocks overlying the above- 

 mentioned Danian limestone may represent this epoch. 



Oligocene and Miocene. — By the close of "Eocene" times the 

 mountains formed during the Cretaceous crust-folding had been 

 reduced approximately to a peneplain and the marine trans- 

 gressions of "Oligocene" and "Miocene" times submerged the 

 greater portion of the South Island, and much of the North Island, 

 and a very rich molluscan fauna was present. There was, however, 

 considerable local variation in the development of such marine 

 rocks, a discussion of which would necessarily lead into much 

 detail, with the difficulties of conflicting correlations and a con- 

 fused nomenclature. It should, however, be noted that in the 

 central region of Otago in the South Island, where, it is suggested, 

 the recumbent folds of the Cretaceous orogeny were most highly 

 piled, reduction by erosion and subsidence seems to have been 

 retarded, so that this region remained above the level of the Tertiary 

 sea, but in "Miocene" and perhaps also in "Pliocene" time was 

 largely covered with fluviatile and lacustrine deposits, often richly 

 auriferous. 



Pliocene. — Crust- warpings at the close of "Miocene" times 

 caused the sea to retreat from the greater part of the South Island, 

 though it transgressed on to its northeastern angle. The North 

 Island, however, was largely if not completely submerged, except 

 for the great volcanoes which now commenced their activity. In 

 this transgressive sea "Phocene" beds were laid down, in some 

 cases with quite noticeable unconformity upon "Miocene" beds. 

 One district calls for special mention, that of Wanganui in the 

 southwestern portion of the North Island which must surely 



