226 Transactions. 



tions. As time went or. more and more of the loose sediments was re- 

 moved, and the original form of the land-surface completely altered. 



The existing Tertiary deposits are in all probability but a small part 

 of those originally laid down, for isolated fragments of these rocks are 

 found in various places high above the present valley-floors, and in such 

 positions that they may well have formed part of an extensive sheet. I 

 think that this is the best explanation of the evolution of the land in the 

 district, as well as of the anomalous courses of the rivers. A similar 

 explanation was also indicated by Captain Hutton in a short paragraph 

 contained in his paper on " The Formation of the Canterbury Plains ' 

 (Trans. N.Z. Inst., vol. 37, 1905, p. -167). 



It is quite possible, however, that the presence of the Lower Waipara 

 Gorge in the peculiar situation in which it now occurs may be due to a 

 small coastal stream cutting back its head through the escarpments of 

 harder rocks, capturing the headwaters of other small streams, and finally 

 tapping the Waipara itself; but the explanation based on the fact that 

 it is a case of " superimposed " drainage fits the case best. 



Stratigraphy. 



The question of the stratigraphy can naturally be elucidated by a 

 comparison with other known localities. Fortunately, the Mid-Waipara 

 and the Weka Pass (in close proximity) have become classic in the history 

 of New Zealand geology, having been reported on by nearly all those 

 who have done field-work in this country. In these typical localities the 

 following is a representative sequence, starting from the top, of the beds 

 that have been recorded : — 



8. Motunau or Greta Beds. — Sands and conglomerates, mostly calcareous, 

 with shells of Mollusca in varying states of preservation, but 

 usually fragmentary. The beds are generally loose and incoherent, 

 but at time concretionary. 



7. Mount Brown Beds. — Rough calcareous sandstones with harder con- 

 cretionary bands, markedly fossiliferous in places. 



6. Grey Marl. — Grey and greenish sandstones and blue sandy and cal-* 

 careous clays. 



5. Weka Pass Stone. — Glauconitic and slightly arenaceous limestone. 



4. Amuri Limestone. — Foraminiferal and argillaceous limestone. 



3. Greensands. — Markedly glauconitic in the upper portions, and with 

 concretions full of saurian remains in the lower part. These beds 

 arc often argillaceous, ferruginous, and calcareous, and at times 

 exhibit marked efflorescence of sulphur. 



2. Oyster - beds, containing shells of Ostrea, Gonchothyra parasitica, 

 fragments of Belemnites, Inoceramus, and other shells. 



1. Sands and clays with brown coal and impure limonite. 



The lower portion of this series is more completely developed further 

 to the north-east, in the Omihi Creek and at Amuri Bluff. According 

 to Hector, Haast, Hutton, Park, and perhaps McKay, the sequence is 

 broken by unconformities, placed in different positions by the different 

 authors, but it is very probable that it is quite conformable throughout. 

 However, it is only the upper part of the sequence with which this paper 

 is specially concerned — that is, with the Motunau and Mount Brown beds, 

 and the Grey Marls and Weka Pass beds, which underlie them. The 

 whole of the banks and terraces bordering the Waipara River as it passes 

 through the lower gorge consist of the sands and conglomerates forming 



