Geological Society of London. 27 



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 Nga Tutura, an Extinct Volcano in New Zea- 

 land." By Capt. F. W. Hutton, F.G.S. 



This volcano is situated on the west coast of the North Island of 

 New Zealand, between Eaglan and the mouth of the Eiver "Waikato. 



A section of 15 miles is exposed along the coast, which trends in 

 a north-west and south-east direction, showing beds of Mesozoic age 

 forming a synclinal trough between the south head of Waikato and 

 Otehe Pointj and descending below the sea-level at Waikawau. 

 Upon them lie Tertiary strata, following the same synclinal curve as 

 the older rocks, and broken through, nearly in the centre of the 

 curve, by the basaltic cone of Nga Tutura. This volcano is about 

 600 feet high, and is chiefly composed of basaltic lava-streams, with 

 but little tuff. The eruption is considered by the author to have 

 been submarine. 



Captain Hutton then stated his conviction that the fluid matter 

 which escaped was not connected with a central molten interior of 

 the earth, but was derived from rocks not much more than 1000 

 feet in depth, and that the synclinal in question was caused by a 

 subsidence into the cavity thus formed. 



Discussion. — Prof. T. Eupert Jones would be glad to hear Dr. 

 Hector's opinion on the subject before Mr. Heaphy's views were 

 entirely condemned. 



Mr. David Forbes could not see that the author had brought any 

 conclusive proof that the lava was derived from so inconsiderable a 

 depth. From his examination of the lavas of Polynesia, of Europe, 

 and of other localities, he was satisfied that their chemical constitu- 

 tion was the same, and therefore that their products were derived, 

 not from any merely local sources, but from some more or less con- 

 nected extensive internal reservoir. In answer to Sir C Lyell. he 

 showed, from the eruption of Santorin, that the trachytic and basaltic 

 lavas came from the same source, inasmuch as they issued from one 

 and the same crater. 



Mr. W. W. Smyth was gratified that one of the results of the new 

 system of education of military officers was productive of such good 

 results in a geological point of view. 



3. " On Bahosaurus." By J. Wood Mason, Esq., F.G.S. The 

 Kimmeridge Clay of Shotover Hill has yielded five specimens of the 

 teeth of this reptile, now for the first time represented as a British 

 genus. After noticing the bibliography of the subject, and the pre- 

 sence of specimens in various museums, the author proceeded to de- 

 scribe the characters of the teeth. They are large, conical, incurved, 

 and slightly recurved, having two sharp, prominent, crenulated, 

 longitudinal ridges, which are situated midway between the convex 

 and concave curvatures. 



