454 Transactions. — Geology. 



than the preceding one ; and they mark, I believe, the gradual 

 dying-out of volcanic activity along the Waitakerei Eange. 



The general evidence for the age of the beds is of a three- 

 fold character. In the first place, there are the fossils con- 

 tained in the beds themselves — the palseontological evidence. 

 This alone would show that the Cheltenham breccia cannot 

 be Pliocene, as the Geological Survey contends. In the 

 second place, there is the composition of the contained lava. 

 In New Zealand, as in other places, there seems to be fre- 

 quently a regular succession. The earlier eruptions are 

 sometimes basic. These, however, are succeeded by acid 

 lavas, and these again by more basic, the lava of a " petro- 

 graphical province " growing more and more basic till the 

 cycle is completed. The lavas of Pliocene age in Auck- 

 land are olivine basalts. The lavas of the volcanic beds of 

 the Waitemata series are pyroxene-andesites ; and, since the 

 Eocene lavas are generally rhyolites, the evidence seems at 

 least favourable to a Miocene or Oligocene age for the Waite- 

 mata lavas. The exceptions to this rule make it impossible, 

 however, to rely on the lithological evidence alone — or, indeed, 

 to lay much stress upon it. The last line of evidence is the 

 position of the beds — the stratigraphical evidence. At Orakei 

 Bay there is a very fossiliferous greensand of whose Miocene 

 age there can be little doubt. It will be shown that the vol- 

 canic beds are all below the greensand, with the exception of 

 the Parnell grit, which is above it. 



Generally the beds of the Waitemata series are either 

 horizontal or dipping in long gentle anticlines and syn- 

 clines ; but in places they are distorted and dislocated, and 

 may even be thrust over each other. It has been generally 

 supposed that these strains and the numerous faults are due 

 to the volcanic forces which produced the basalt puys, 

 scattered in scores round the Waitemata. Sometimes, per- 

 haps generally, the distortions occur in proximity to a puy. 

 At other times no such apparent connection is visible, and 

 the strata may be disturbed far from any basalt cone, or may 

 lie horizontally quite close to one. It may be that the small 

 puvs are no true measure of the magnitude of the volcanic 

 forces that formed them, and that, as in Scotland, when 

 denudation lays bare the underlying rocks great sills will be 

 found whose contents never reached the surface.* 



In working out the stratigraphy of the Waitemata series 

 the volcanic beds are invaluable. They are widespread, and 

 their lithological characteristics are much more distinct than 

 those of the sandstones and shales. Moreover, some of the 



* Sir A. Geikie : "Ancient Volcanoes of Great Britain," vol. i., 

 p. 458. 



