Uttley. — Geology of llit Oamaru-Papakaio District, 



121 



diatomaceous earth, and the latter is altered in places to a hard flinty 

 rock. There are inclusions of quartz in the dolerite, this being a notice- 

 able feature of the earlier intrusive rocks associated with the Waiareka 

 tuft's. The quartz has probably been incorporated during the passage of the 

 molten rock through the quartz grits that lie at the base of the Tertiary 

 series. The limestone is poor in fossils, and is similar to the building-stone, 

 but in parts it becomes chalky. A peculiar nodular surface marks the 

 junction of this rock with the overlying greensand, although it is not so 

 conspicuous in this locality as in other parts of the district. The green- 

 sand (c) overlying is glauconitic, casts of Foraminifera being plentiful. 

 Some distance above the base Pachymagas parki (Mutt.) occurs in abund- 

 ance, other fossils being scarce. The brown sands (d) are also glauconitic 



a 2 

 Fig. 



a, 



h C nL 



2. — Section (diagrammatic) W.N.W. -E.S.E. through the Devil's Bridge. 

 (a) Tuffs and diatomaceous earth, intruded by dolerite (fflj); (ft) lime- 



stone ; (c) greensand ; (d) Awamoa beds ; (e) gravels. 



and very fossiliferous. The nodular band contained Terebratula sp.. Aetheia 

 gualteri (Morris), Hemithyris sp., and stems of Isis. The greensand (c), in 

 addition to Pachymagas parki (Hutt.). contained Pecten huttoni Park. The 

 fossils from the brown sands (d) have been recorded by Marshall and Uttley 

 (1913, p. 303) and clearly indicate that the beds are Awamoan. 



Park (1905, p. 518), in describing the beds here, placed the limestone 

 above the Hutchinsonian and Awamoan ; but the greensands lie hard upon 

 the surface of the limestone, which is undoubtedly the Ototara stone. The 

 rocks are conformable throughout, and dip towards the coast at an angle 

 of from 10° to 16°. 



2. Grant's Stream. Ardgowan. (Fig. 3.) 

 At Ardgowan, near the junction of Grant's Stream with the Oamaru 

 Creek, a small section is exposed on the roadside. The lowest beds (a) 

 consist of a brecciated pillow-lava, which can be traced in a continuous 

 section along the banks of Oamaru Creek to the town of Oamaru. This 

 bed is overlain by a limestone (b) 10 ft. 

 thick, containing occasional water-worn 

 masses of decomposed vesicular basaltic- 

 rock. This passes into an indurated 

 limestone (c), which becomes nodular 

 at its junction with the greensand (d). 

 The nodular portion contains many 

 fossils, but chiefly as casts. Stems of 

 Mopsea also occur. The actual junc- 

 tion with the overlying greensand (d) 

 is not seen, as the latter occur sepa- 

 rated from the main exposure. From the nodular surface of the lime- 

 stone I obtained the following forms: Turbo sp., Polinices sp., Turritella 

 sp., Lima lima (L.), Ostrea sp., Cardium sp., Liofhyrella boehmi Thomson, 

 Terebratulina suessi (Hutt.), Aetheia gualteri (Morris), Hemithyris sp. The 

 section is interesting as it indicates clearly the horizon of the volcanic 

 rocks, which are here about 20 ft. below the nodular bed. 



Fig. 3. — Section at Ardgowan. (a) Brec- 

 ciated pillow-lava, &c. ; (ft) limestone 

 (with rounded boulders); (c) limestone; 

 (d) greensand ; (e) gravels. 



