1868.] MASON DAKOSAURFS. 15 



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 consti- 

 tution 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 the new system of education 

 of military officers was productive of such good results in a geological 

 point of view. 



3. On Dakgsatjrtjs. By J. Wood Mason, Esq., E.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, cre- 

 nulated, 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 Varanidce. If 

 the materials were at hand for a complete definition of its compa- 

 rative osteology, Dahosaurus would probably exhibit a combination 

 of Lacertnian and Crocodilian characters, but with the crocodilian 

 elements predominant. 



