Marshall. — The Tawhiti Series, East Cape District. 109 



Art. XVIII. — The Tawhiti Series, East Cape District. 



By P. Marshall, M.A., D.Sc, F.G.S., F.N.Z.Inst., Hector and Hutton 



Medallist. 



[Read before the Wanganui Philosophical Society, 3rd December, 1919 ; received by 

 Editor, 31st December, 1919 ; issued separately, 10th June, 1920.] 



The true geological position of the strata that are exposed on the coast- 

 line between Tokomaru Bay and the East , Cape has never been definitely 

 ascertained, for we have had to rely on rather incomplete statements of 

 McKay. Fossils of a true Cretaceous nature were reported as occurring 

 in some abundance near Awanui. I visited the district in January, 1919, 

 in company with Mr. J. A. Bartrum, with the primary object of making 

 collections of fossils from the localities that were mentioned by McKay, 

 in the hope that study of them would be of assistance in unravelling some 

 of the debated points in regard to the relationship of the Cretaceous rocks 

 to those of Tertiary age in New Zealand. 



We spent two days on the coast near Awanui, but failed to find any 

 of the ammonites and other fossils that were mentioned by McKay.* 

 The only fossil remains that we found were some fragments of Inoceramus 

 near the wharf at Awanui and a number of small worm-tubes a little to 

 the north of that place. Inoceramus was very abundant in the con- 

 cretionary boulders on the north side of Tuparoa Bay, and there were also 

 fossils in the marls on the south side of the bay. These, however, were 

 badly preserved, and seemed to be of a distinctly Tertiary nature. The 

 stratigraphy is extremely involved, and the strata have slipped so much, 

 while the sections are so discontinuous, that in the limited time at our 

 disposal we were quite unable to come to any detailed conclusions on the 

 question of the relationship of the strata. 



At Tawhiti Point, on the north side of Tokomaru Bay, fossils are 

 quite numerous, and they are also abundant in the shell conglomerate 

 which occurs on Tawhiti itself at an elevation of 500 ft. or more. From 

 ■the former of these localities over a distance of about a mile along the coast 

 from Kotunui Point a representative collection of fossils was made. McKay 

 collected from these beds in 1872, and he made a further reference to them 

 in 1886, when he classed them of Upper Miocene age.| 



Hutton,J in his paper on the geology of New Zealand, places the Tawhiti 

 beds in the Pareora system, which is regarded by him as the equivalent 

 of the Miocene of Europe. 



No list of fossils that were found in these- rocks has yet been published. 

 The rocks are described by McKay as soft brown sandstones. We found 

 that in their unweathered state they are of a grey colour and fine-grained. 

 They are formed partly of small grains of quartz, with a good deal of 

 partly-weathered feldspar, and black grains which seem to be volcanic 

 glass. It is almost certain that the sand is of volcanic origin. The 

 strata are considerably inclined, and strike 41° and dip 37° north-west. 

 The thickness of the strata of which Tawhiti is composed is very consider- 

 able. Tawhiti itself rises to a height of 1,670 ft., and if the strike and 



* A. McKay, '^ep. Geol. Explor. dur. 1873-74, 1877, p. 124 ; 1886-87, 1887, p. 214. 

 t A. McKay, Rep. Geol. Explor. dnr. 1873-74, 1877, p. 147 ; 1886-87, 1887, p. 210. 

 X F. W. Hutton, Quart. Journ. Geol. Soc, 1885, p. 209. 



