Speight and Wild. — Weka Pass Stone and Amuri Limestone. 87 



South Side of Amuri Bluff. 



In this locality the sequence is well exposed on the finely developed 

 shore-platform on the south side of the bluff and around the coast-line as 

 far as the mouth of the Okarahia Creek. Above the nodular layer there 

 is about 15 ft. or so of limestone, and this is succeeded conformably by a 

 greenish calcareous sandstone, perhaps the equivalent of the lower part of 

 the typical grey marl, or perhaps, as is more likely, the equivalent of the 

 Weka Pass stone. The upper portion passes into a typical marl of decidedly 

 argillaceous character. Hutton considered that this locality furnished 

 strong evidence of unconformity between the grey marl and the Amuri 

 limestone, his main line of evidence being the discordance in the dip of the 

 former as it occurs in the neighbourhood of the mouth of the Okarahia 

 Creek and south of it with the limestone at the bluff. This apparent dis- 

 crepancy in angle of dip is due to folding and twisting movements 

 affecting the beds unequally in the two localities. The limestone south of 

 the creek dips at a very high angle, and the marl is in perfect accord with 

 this ; while when traced in a north-easterly direction towards the bluff the 

 beds flatten out, and nowhere present any evidence of discordance. 



Evidence that the Series is Conformable. 



This detailed account of the sections taken from widely separated parts 

 of the area gives some idea of the general nature of the contact and empha- 

 sizes the similarity of its features. Relying entirely on the evidence of the 

 borings in the upper surface of the Amuri limestone and the presence of 

 detached fragments of the limestone in the greensand matrix of the nodular- 

 layer. Hutton and Morgan came to the conclusion that it was a true erosion 

 surface, the supposition being that the erosion took place in the vicinity 

 of a shore-line. No palaeontological evidence was advanced by either in 

 support of their contention as regards the two limestones, the reason being 

 that they are both, the Amuri limestone especially, according to Hutton, 

 almost unfossiliferous ; thus in their opinion the existence of an uncon- 

 formity rests entirely on stratigraphical evidence. We, however, relying 

 on stratigraphical evidence, have come to a conclusion that the sequence 

 is conformable, the reasons for this conclusion being as follows : — 



1 . In every case there is absolute agreement in the dip of the beds above 

 and below the nodular layer. When this occurs over a region of a hun- 

 dred miles in length by some fifteen in breadth, unconformity appears 

 extremely doubtful. It means that a limestone has been laid down on a 

 deep-sea bottom, the rock has become consolidated, raised above the sea, 

 eroded, and again depressed into deep water so that another layer of 

 calcareous material may be deposited, and all this without any variation 

 in angle due to structural movements or to conditions of deposition over 

 hundreds of square miles. Such a contention appears unreasonable. 



2. Apart from the evidence furnished by the included fragments of 

 limestone in the nodular layer, and the report of the occurrence of pebbles 

 of greywacke at Stonyhurst, which can be explained as probably the result 

 of mistaken identification, there is no evidence of erosion of the upper sur- 

 face of Amuri limestone. On any present-day surface of Amuri limestone 

 there are distinct irregularities, and especially is this the case on the shore- 

 platforms where tidal channels, &c, are a marked feature, and none of these 

 are to be seen at any part of the contact, although it is exposed for many 

 miles in different parts of the area, not only parallel but at right angles to 



