3. The Volcanic Beds of TheSeries.
As the volcanic beds at Cheltenham and Parnell are the thickest, most fossiliferous, characteristic, and widely spread beds of the series, and their stratigraphical position and age have been a subject of much dispute, most of the paper will be devoted to a consideration of them. The evidence tends to show that they are distinct beds, though Mr. McKay and Mr. Park consider them identical, and Mr. Park writes that he has “conclusively proved” their identity. Sir James Hector considers the Cheltenham breccia to be Pliocene, so that it will be necessary to give in some detail reasons for supposing it to be Lower Miocene, or even Oligocene. With regard to its source, I will give evidence tending to show that it probably came from the Waitakerei vents. The chief point
of interest with regard to the Parnell grit is whether it is above or below the Orakei Bay greensand, because the latter is a fossiliferous bed which is allowed to be Miocene. Mr. Park felt inclined to place it below, although admitting the evidence inconclusive, and he has since classed it as Eocene.* But a large amount of new stratigraphical evidence will be given which leads me to think that it is really above the Orakei greensand, and therefore Miocene. Its source is an open question; it may have come from the Waitakerei, but there is evidence in favour of its having come from the Coromandel vents. There are at least two other volcanic beds. One of these really consists of a group of tuffs separated by thin layers of shale. They are well developed at Wairau Creek, and so I have called them the “Wairau tuffs.” The other bed is a feldspathic tuff, developed best at Ponsonby, and called throughout the “Ponsonby tuff.” These can be dealt with more shortly.
I consider that the thick volcanic breccias on the west of the Waitakerei Range should really be included in the Waitemata series, but I have not been able to examine them sufficiently to include a discussion of them in this paper.
[Footnote] * “Thames Goldfields”: Park and Rutley, 1897.