Thomson. — Flint-heJs associated irifli Aiiikii /.uittsfone. 49 



reached by Hector (1890), McKay (1891), and Cotton (1913). In thickness, 

 however, it is very variable, being less than 300 ft. in the "Waipara district, 

 and, together with the flint-beds, over 2,500 ft. in the Middle Clarence 

 Valley. At Amuri Bluff, roughly half-way between these places, the thick- 

 ness is estimated by Hector (1877) at 780 ft., and it probably increases 

 gradually between this point and the Middle Clarence Valley. Near Keke- 

 rangu the limestone appears to be divided into two or three parts by mud- 

 stone intercalations, but it is possible that this appearance is deceptive, 

 and is due to faulting or sharp folding, since a mudstone overlies the lime- 

 stone. A somewhat similar phenomenon occurs in the hills north of the 

 Lower Ure River. The thickness of the formation decreases again in the 

 Cape Campbell district, but it is still considerable. Apparently the typical 

 Amuri limestone reappears on the north side of Cook Strait in the Cape 

 Palliser district, but it has not been personally investigated in that area by 

 the writer. 



The age of the Amuri limestone is approximately fixed by the fact that 

 it always overlies beds containing Cretaceous fossils, and is always followed 

 by beds containing a Tertiary (Oamaruian) fauna. In all localities where 

 a continuous section can be traced the limestone follows the Cretaceous 

 beds with complete conformity of bedding ; and in localities south of 

 Amuri Bluff there is also a lithological gradation between these two sets of 

 rocks, proving that the apparent conformity is there a real one. The 

 Amuri limestone is thus much older at its base, even where it is thinnest, 

 than any beds in the Oamaru district ; and the diastrophic correlation of 

 the Amuri and Ototara limestones by Marshall, Speight, and Cotton (1911) 

 is in conflict with the' palaeontological evidence. The Cretaceo-tertiary 

 problem in New Zealand owes much of its complexity to an earlier false 

 correlation of these rocks, which, it may be noted, was never accepted by 

 Hutton. Within the central part of New Zealand, where the Amuri lime- 

 stone is developed. Cretaceous beds always underlie the limestone con- 

 formably, while it is followed by physically conformable beds containing 

 an Oamaruian fauna. Outside this area — at any rate, to the south of 

 it — the sequence generally commences with Oamaruian coal-beds, and. in 

 the few areas where Cretaceous rocks are developed, there is probably 

 unconformity. 



In the Waipara district the Am'uri limestone is followed by a calcareous 

 sandstone, the Weka Pass stone, and this in turn is followed by more or 

 less calcareous mudstones, the " grey marls." In places the Weka Pass stone 

 is glauconitic at the base, and in such places there is the peculiar and often- 

 described junction which gives the appearance of an erosion of the lime- 

 stone prior to the deposition of the glauconitic bed. Whether or not 

 this is a correct explanation of this peculiar contact, it is certain that no 

 such contact is present at places within the same district where the base 

 of the Weka Pass stone is not glauconitic, but that there is a passage so 

 gradual between the two rocks that one cannot say within a foot of rock 

 where the one ends and the other begins. It is, therefore, evident that 

 even if there has been some erosion of the Amuii limestone prior to the 

 deposition of the Weka Pass stone, it is a purely local phenomenon, and 

 not indicative of a non-sequence of any extent. The argument that 

 an unconformity between the two limestones may well be present from 

 the analogy of similar well-proved unconformities in other parts of the 

 world entirely overlooks the facts that in these other places the apparent 

 conformity of the two limestones in question is local, and that in New 



