402 R. Lydekker — Teeth of Hycenodon. 



"A. "When the Chanter's Seat conglomerate was formed the following rocks were 

 undergoing denudation : — 



(1) Granitoid rocks, identical with the existing Dimetian. 



(2) Trachytic rocks, among which were probably true lava-flows. 



(3) Quartzites and schists, the latter resembling those which in many districts 

 occur rather high in the Archsean series. 



(4) Ordinary sedimentary rocks. 



Hence there was in this district a series of rocks, some much older than others, 

 which contributed to the formation of the Cambrian conglomerate. 



B. The conglomerate above the Trefgarn series is formed from rocks which occur 



in the latter. 



C. The peculiar characteristics distinctive of certain members of the Trefgarn 



series had been assumed by them when the conglomerate was formed. 



D. Either the Dimetian is a member of an old gneissoid series or, if it is the core 



of a volcanic group from which the trachytic lavas had been ejected, this 

 had been laid bare by denudation before the Cambrian conglomerate was 

 formed. Hence in either case both the Dimetian and the felstones are 

 Pre-Cambrian." 



In the Q.J.Gr.S. vol. xl. Mr. T. Davies, in addition to describing 

 numerous slides prepared from pebbles of felsites, quartz-felsites, 

 basic volcanic rocks, porcellanites, etc., derived from the Cambrian 

 Conglomerates and proved to be identical witb the rocks of that 

 character in the Pebidian series, makes the following statement, 

 at p. 555, concerning the fragments of Dimetian in the con- 

 glomerate : " The view that the Cambrian conglomerate of St. 

 Davids incloses much waterworn debris of the Dimetian is, I 

 think, fully justified by the evidence now adduced from the examina- 

 tion of many slides of this rock, few of which have failed to afford 

 evidence of the presence, not only of pebbles of a rock, which under 

 the microscope could not be distinguished from it, but also of its 

 individual mineral constituents. The slides examined and described 

 here are not selected ones, but have been taken as they were cut. 

 The peculiar quartz of the Dimetian, thronged as it is with extremely 

 minute inclosures other than fluid, causing its well-known dirty 

 aspect, is abundant. The felspars of both rocks are of the same 

 character and habit, although necessarily more fragmentary in the 

 conglomerate. Though not abundant, they are there, and can be 

 most distinctly recognized. In some cases they are not more altered 

 than in the Dimetian ; but in others the structure has entirely 

 disappeared, leaving a kaoline-like mass which feebly depolarizes 

 light." 



I may add that I am quite ready to submit the slides on which the 

 above statements were founded, along with others since prepared, if 

 possible containing still more conclusive evidence, to any unbiassed 

 petrologist. 



VI. — Note on certain Teeth referred to Et^nodon indicvs. 

 By B. Lydekker, B.A., F.G.S., F.Z.S., etc. 



IN the " Paleeontologia Indica," ser. 10, vol. ii. p. 319, fig. 21, I 

 described and figured a lower premolar from the Siwaliks of 

 the Punjab, under the name of Hytenodon indicus ; the figure being 

 reproduced in the accompanying woodcut (Fig. 1). 



