1868.] HIITTON EXTINCT VOLCANO. 13 



Mr. Babbage suggested that, assuming an eruption of lava at the 

 bottom of the ocean, there might be such an amount of steam gene- 

 rated, 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 ITga Tutuea, an extinct Volcano in New Zealand. 

 By Captain F. W. Hutton, E.G.S. 



On the west coast of the JS'orth Island of New Zealand, between 

 Raglan and the mouth of the river AYaikato, there exists an extinct 

 volcano, called Nga Tutura, which, owing to its position on the sea- 

 cliif, is of considerable interest. 



The south head of the Waikato is composed of a series of indu- 

 rated shales and sandstones, containing Belemnites AucMcoidicus, 

 Hauer, Ancella plicata, Fitt., and many fossil ferns. This series 

 is supposed to be of Upper -Mesozoic age, and has here aj^dip of 

 about 35° JSr.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 E-aglan, 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. Fii-st comes a coarse-grained lime- 

 stone, six or eight feet thick, often passing almost into a conglomerate 

 at its base, but more j)ure 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 sand- 

 stone, about 100 feet thick, containing jSchizaster rotundatus, Fitt., 

 Scalaria lyrata, Fitt., Pecten Williamsoni, Fitt., &c. This bed gets 

 coarser-grained and more siliceous to the north, and more calca- 

 reous 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, con- 

 tain the remains of existing plants ; and therefore their age is, pro- 

 bably, 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. 



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



