Speight and Wild. — Weka Pass Stone and Amuri Limestone . 77 



A well-defined fault-scarp runs along the eastern face of the mountain in a 

 north-west and south-east direction in a line with the western margin of the 

 depression which continues towards Heathstock and the Upper Waipara 

 basin. On the western side of this, in the vicinity of Mount Mason and 

 elsewhere, there is evidence of deformation where the limestones abut against 

 the older rocks. This line of deformation evidently belongs to the series of 

 north-west and south-east earth-fractures which are characteristic of the 

 mountain region of Canterbury. As a result of this and related movements 

 the Mount Brown beds and the underlying limestones are bent round till 

 on the divide between Boby's Creek and Kowai Biver they strike north- 

 west and dip to the north-east at high angles, about 70°. The edges of the 

 beds are thus exposed, and the relations of the Amuri limestone to the beds 

 immediately overlying it are well seen in one or two places. The sequence 

 is here as follows : — 



(1.) Amuri limestone, of the usual type, well jointed, and not more 

 than 25 ft. thick ; it thus shows the characteristic thinning- 

 out as it approaches a shore-line. In its upper layers it is glauco- 

 nitic, and deeply bored, with the borings filled with greensand. 

 (2.) Nodular layer : This is about 4 ft. wide, with pieces of limestone in 

 a matrix of greensand. This bed is closed with a fairly well- 

 defined layer of fragments in which limestone predominates over 

 greensand, as if there were a partial reversion to limestone con- 

 ditions when this part of the bed was being deposited. The 

 calcareous nodules are distinctly bored, and show a marked 

 qualitative reaction for phosphoric acid. There are occasional 

 small, rounded, dark-greenish nodules, up to f in. in diameter, 

 but these are more important in the next bed. 

 (3.) Calcareous greensand, strongly glauconitic. It appears that the 

 Weka Pass stone takes on this decidedly glauconitic facies as 

 it approaches a shore-line, and also the phosphatic nodules are 

 apparently more numerous under these conditions, suggesting a 

 resemblance to the conditions obtaining on sea-bottoms of the 

 present day where greensands and green muds are associated 

 with these nodules. 



South Branch of Omihi Creek. 



South-east of the Omihi Valley, and dividing its drainage area from that 

 of the slopes facing seaward, lies the prominent limestone escarpment of the 

 Cass, or Limestone, Bange as it is sometimes called. On its northern side 

 there are excellent exposures of the limestones and the underlying sands 

 and sandstones resting unconformably on the Trias-Jura beds. Owing to 

 a fault which runs approximately north-east and south-west, with a throw 

 of some 1,000 ft. to the north-west, the outcrops are repeated, and we thus 

 get two sections which show the horizon of the nodular layer. They exhibit 

 a striking difference, however. One section has a facies which shows the 

 proximity of a shore-line, in agreement with the fact that the Trias-Jura 

 beds are in evidence but a few hundred yards away in the direction of the 

 rise of the beds, whereas the other section, about a mile and a quarter to 

 the south-east, has a facies which is characteristic of deeper water. 



The first of these sections is well displayed near a small waterfall on 

 the east side of the road which runs south past the shepherd's hut in the 

 direction of the limestone escarpment. The typical Amuri limestone is here 



