Thomson. — Geology of Middle Waipara and Weka Pass District. 411 



limestone is absent from part of the Piripaiian area — viz., the Malvern 

 Hills — and. according to Chapman's determination of the age of the 

 supposed Amuri limestone of the Trelissick Basin, from that area also. 

 Whether this absence is due simply to the replacement of calcareous by 

 clastic deposits on approaching the shore-line, or to local uplifts, remains 

 uncertain. If the former were the case a littoral fauna of different age 

 from the Piripauan should be found. What remains certain is that the 

 Amuri limestone sea did not appreciably widen its borders over the Piri- 

 pauan sea, though it was probably deeper, and consequently we cannot 

 speak of a Kaitangatan transgression in North Canterbury, but must 

 suppose that the Piripauan sea was deepened, without being extended, 

 by local downwarping or block-faulting. 



The succeeding Oamaruian rocks, which can hardly demand as deep 

 a sea as the Amuri limestone, transgress widely over the latter formation 

 to the, west and south, and the extension of the sea-margin thus indicated 

 was not a gradual one but a sudden one. The surface of the land before 

 this transgression is known to have been of very low relief — i.e., a peneplain 

 ■ — and the attainment of such a surface demands a period of standstill of 

 the strand-line.* This is in accord with the contact between the Weka 

 Pass stone and the Amuri limestone, which represents a period during 

 which deposition practically ceased, perhaps b}^ a shallowing due to 

 regressions, and boring and solution of the upper surface of the Amuri 

 limestone took place. The general lithological similarity of the Oamaruian 

 beds of South Canterbury with the Piripauan beds of North Canterbury 

 suggests similar conditions of coastal relief, so that, although there is direct 

 evidence for a sufficiently diversified surface during the Piripauan to admit 

 of overlap, the relief must have been small. Consequently the period of 

 time recjuired for peneplanation during standstill of the strand was probably 

 not great. The significance attached to the contact between the Amuri 

 limestone and Weka Pass stone by Hutton and Park, as representing a 

 period of uplift and great erosion, was a mistaken one, and the time interval 

 between the two rocks was very much less than they supposed. Never- 

 theless the contact was a correct one to choose for classification, and. 

 Hutton's Waipara and Oamaru systems are two well-defined natural 

 divisions of the rocks in North Canterbviry, whereas Hector's Cretaceo- 

 Tertiary formation was an unnatural one. 



The Oamaruian transgression and regression were not perfectly regular 

 eustatic movements with the Ototara limestone as the middle member 

 representing the period of maximum depression of the land. The contact 

 between the Ototara limestone and the Hutchinson Quarry greensand is 

 very similar to that between the Amuri limestone and Weka Pass stone, 

 and was probably due to a similar cause — viz., a sudden shallowing of 

 the sea, followed by a period of standstill, There is a similar contact in 

 South Canterbur}' between a lower foraminiferal limestone and an upper 

 polyzoan limestone or calcareous sandstone exhibited both at Waihao 

 and on Mount Craigmore, in the Pareora district. No palaeontological 

 evidence is forthcoming, however, for the correlation of these two phos- 

 phatic horizons, and in the Totara Valley, near Pleasant Point, there is 

 another phosphatic horizon at the top of the upper limestone. Similarly, in 

 the Waipara district, the presence of bored contact between the 'Weka Pass 

 stone and the "grey mayls," and the unconformities in the latter rocks and 

 between them and the lower Mount Brown limestone in the Weka Pass, are 

 suggestive of considerable oscillation of movement during the Oamaruian. 



* I am indebted to Dr. Cotton for calling my attention to this important conclusion. 



