Thomson. — Stage Names applicable to Divisions of Terfiari/. 33 



Tliere is a great escarpment of limestone, first described, by \V. Mantell 

 (1850), and by ]iim named the Ototara limestone, which runs from the 

 neighbourhood of Kakanui for several miles in a northerly and then north- 

 westerly direction towards the Awamoko River. The escarpment overlooks 

 the Waiareka Valley opposite Alma and at Enfield, and the rock dips in 

 an easterly direction towards Weston and Totara, where the Oamaru lime- 

 stone quarries are situated. The Oamaru building-stone, the Oamaru 

 limestone of Park (1905), is thus the Ototara stone, although Park in 1910 

 calls his supposed upper limestone the Ototara stone and the lower lime- 

 stone the Oamaru stone. The dip of the beds does not remain long constant 

 to the east, however, for the limestone reappears at numerous points in 

 the triangle of country between the main escarpment, the sea-coast, and 

 the AVaitaki Valley. In all clear exposures the overlying beds are found 

 to consist of calcareous greensand, often crowded with brachiopods, and 

 generally known as the Hutchinson Quarry beds. The junction between 

 the greensand and the limestone is not a simple one, for the upper surface 

 of the limestone is often very irregular, and in many places covered with 

 a brown varnish which has proved to be phosphatic {e.g.. All Day Bay, 

 Kakanui, Deborah, Devil's Bridge). In the upper layers of the limestone 

 there are frequently rounded calcareous concretion-like masses, varying 

 in size up to 3 in. or 4 in. in diameter, and containing tissue-like com- 

 partments within, suggesting an algal growth. The basal layers of the 

 greensand are crowded with segments of Mopsea hamHtoni (Thomson), 

 often in a phosphatized condition, while both unaltered and phosphatized 

 brachiopods may be obtained. This peculiar junction has some analogies 

 with that between the Weka Pass stone and the Amuri limestone, and 

 seems to correspond to an abrupt change of conditions. It almost cer- 

 tainly denotes a non-sequence, though not in most places physical uncon- 

 formity ; but there is no reason at present for believing that the non-sequence 

 is of any great extent. At Hutchinson's Quarry the greensands rest on 

 a concretionary conglomerate consisting of rounded pieces of basalt and 

 concretions similar to those described above, set in a calcareous cement ; 

 this bed, several feet thick, rests conformably on a thin band of hard white 

 limestone, which has recently been determined by Morgan to be phos- 

 phatic, and this latter rests quite unconformably on a series of tuffs 

 containing thin limestone bands. The formation of the limestone at this 

 and other points seems to have been nearly prevented by the amount 

 of volcanic material strewed into the sea, so that the limestone is 

 represented by calcareous tuffs and thin bands of limestone. 



Wherever the greensands of the Hutchinson Quarry horizon can be 

 traced upwards they reveal less and less glauconite, and finally pass into 

 shell-bearing sands and blue sandy mudstones — the Awamoa beds. No 

 higher Tertiary rocks are seen in the Oamaru district. 



In a few localities to the east of the main outcrop of the Ototara lime- 

 stone, notably in the neighbourhood of Kakanui, Deborah, and Cape 

 Wanbrow. exposures of older beds are seen. In all cases these are of 

 volcanic origin, and it is evident at Kakanui, at any rate, that the upper- 

 most of these must represent a replacement of the lower part of the 

 Ototara limestone, since the Kakanui limestone is much thinner than the 

 former and shows no characters which would lead one to suppose it formed 

 at a slower rate, but rather the reverse. 



To the west and north of the main outcrop of the Ototara limestone 

 lies the broad low valley of the Waiareka River, on the far side of which 



2— Trans. 



