president's address — SECTION c. 97 



rocks, of whicli the oldest series is possibly " Eocene," and consists 

 of unfossiliferous shales, sandtones, and locaLy conglomerates with 

 fragments of the underlying Senonian beds ; but m the absence of 

 visible contacts with these, there is no other evidence of their un- 

 conformity thereon. The sucoDeding group of beds (the Te Arai 

 Series), referred to the " Lower Miocene," does, however, rest 

 with unccnfoi'mity upon the "Eocene" bods. It is composed of 

 grits and cwiglomerates passing up into claystone and standstone, 

 and may be as much as 8,000 feet thick. The foraminifer Amnhi- 

 stegina and ten molluscs, two of which belong to recent species, 

 are the only fossils known in these beds. The overlying (Tawhiti) 

 formation is much more fossiliferous, and the 'C/vidence of its un- 

 conformity on the "Lower Miocene" beds is seen in sections where 

 gently dipping "Upper Miocene" sandstones rest on strongly 

 crushed "Lower Mioooine" rocks, though beyond those regioins of 

 shattering of "Lower Mioceme" rocks, the "Upper" and "Lower 

 Miocene" beds appear to be quite conformable. (Compare Fig. 5.) 

 Out of a collection of sixty-nine molluscs from this series 25 per 

 cent, proved to belong to' recent species. The brachiopod Pachyma- 

 ga^ {Waiparid) ahnorvris (Thomson) occurs among these. A very 

 similar series of sandstones and calcareous or pumiceous beds, 

 which are probably a conformable and shallow-water transgressive 

 (Ormond) Series on the Tawhiti series, occupies a portion of the 

 area in which the typical Tawhiti beds are not developed. They 

 show a marked unconformity on the Te Arai "Lower Miocene" 

 series when resting on their denuded surfaces. Out of ever 

 100 molluscs therein 50 per cent, belong to recent species. 

 Marshall's (1920) collection of ^fty-two forms from the 

 "Tawhiti" series of Tokomaru, north of the Gisborne 

 district, yielded tha same percentage of recent forms. 

 This striking divergence in percentage of recent forms 

 from those of the Tawhiti series of the Gisborne district, sup- 

 ports the conclusion of Henderson and Ongley that the beds of 

 Tokomaru, placed by McKay (1874), in the Tawhiti series, should 

 rather be grouped with the " Lower Pliocene " Ormond beds. The 

 Ormond beds were apparently elevated, eroded, and depressed before 

 the deposition on them of the "Upper Pliocene" plant-bearing 

 pumiceous silts, &c. Evidence of volcanic activity throughout the 

 Tertiary sequence is to be seen in the tuff beds in the " Lower 

 Miocene," to a less extent in the " Upper Miocene," and in 

 the abundant pumice of both divisions of the " Pliocene" beds. 

 As has been indicated before, Henderson and Ongley hold that 

 this region is divided up into a number of blocks separated by 

 zones of crushing in, which movement occurred at different periods. 

 Some of the faults traversing Cretaceous strata have not affected 

 later beds, and others which made great crush zones in "Lower 

 Miocene" rocks have not effected the "Upper Miocene" beds. 



