Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/83

 Mr. Babbage suggested that, assuming an eruption of lava at the bottom of the ocean, there might be such an amount of steam generated, or even such a decomposition of water, as would originate waves of enormous volume.

Sir C. Lyell was inclined to the same opinion, and not to limit the causes of these waves to oscillations of the surface of the earth. 2. Description of Nga Tutura, an extinct Volcano in New Zealand. By Captain F. W. Hutton, F.G.S.

On the west coast of the North Island of New Zealand, between Raglan and the mouth of the river Waikato, there exists an extinct volcano, called Nga Tutura, which, owing to its position on the sea- cliff, is of considerable interest.

The south head of the Waikato is composed of a series of indurated shales and sandstones, containing Belemnites Aucklandicus, Hauer, Ancella plicata, Fitt., and many fossil ferns. This series is supposed to be of Upper -Mesozoic age, and has here a dip of about 35° N.E. As we follow these beds along the coast in a south- easterly direction, we find their upper surface remaining tolerably level for about four miles, when the dip changes to the south-east, and in half a mile more they have descended below the sea-level, not to be seen again until we arrive at Otehe Point, about halfway between the Waikato and Raglan, where they just make their appearance dipping north, and are immediately cut off by a fault.

Upon these beds Tertiary rocks lie unconformably, the lower portion being considered of Miocene age. First comes a coarse-grained limestone, six or eight feet thick, often passing almost into a conglomerate at its base, but more pure and consisting of fragments of shells and corals and rolled pieces of limestone at the top, and containing Fasciculipora mammillata (Fitt.). This limestone thins out to the north, and is covered by a bed of argillaceous and calcareous sandstone, about 100 feet thick, containing Schizaster rotundatus, Fitt., Scalaria lyrata, Fitt., Pecten Williamsoni, Fitt., &c. This bed gets coarser-grained and more siliceous to the north, and more calcareous to the east. Upon it rests a bed of red or yellow sandstone, sometimes 300 feet thick, interbedded in places with seams of blue clay. These clay beds, and occasionally the sandstone itself, contain the remains of existing plants ; and therefore their age is, probably, Newer Pliocene. This series of Tertiary rocks is horizontal at the mouth of the Waikato ; but further south, where the older rocks begin to dip to the south-east, these newer beds partake also of the same movement, dipping strongly near Waikawan to the south-east, then becoming horizontal, but again dipping 10° S.E. when they reach Kawa. From this point they keep nearly horizontal, broken once only, near Makeo, by a fault, until, on reaching the Otehe Point, they rise up again at the same angle as the upper surface of the Secondary rocks, and are traversed by the same fault.

Very nearly in the centre of this synclinal, the rocks are broken