Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/85

 pears to me to be irresistible that, in this case at least, the fluid matter that escaped as lava was not connected with a melted interior of the earth, but was derived from rocks not more, perhaps, than 1000 feet below the surface. It might, indeed, be urged that the synclinal was not caused by subsidence at all, but by the elevation on both sides when the land was rising above the sea, while the centre was held down by the rivet-like form of the pipe and cone of the volcano. If such an argument should really be advanced in earnest, it would be, I imagine, sufficiently answered by the fact that the pipe of the volcano is almost entirely composed of loose ashes, and not at all equal to bear the strain necessary for such a task.

Discussion.

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 constitution was the same, and therefore that their products were derived, not from any merely local sources, but from some more or less connected 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 the new system of education of military officers was productive of such good results in a geological point of view.

3. On Dakosaurus. By J. Wood Mason, Esq., F.G.S. (The publication of this paper is unavoidably postponed.)

[Abstract.]

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 presence of specimens in various museums, the author proceeds to describe 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.

This reptile is regarded by the author as foreshadowing the form of dentition that characterizes the existing group of Varanidoe. If the materials were at hand for a complete definition of its comparative osteology, Dakosaurus would probably exhibit a combination of Lacertilian and Crocodilian characters, but with the crocodilian elements predominant.