Dr. Henry Hicks — Rocks of St. Davids. 401 



extinct, while others of Neozoic origin, now living, coexisted with 

 them ; and this is not to he wondered at, for in the more ancient 

 geological systems many genera and species ranged from the older 

 to the newer, and were for a time contemporary with more recent 

 forms of life. In the newer stage of the Post-tertiary epoch ( l/olocene) 

 are classed the deposits in which no extinct species have been found. 

 This group is divided into Historic and Pre-historic sub-groups ; and 

 to the latter belong the polished implements of Neolithic age, while 

 the unpolished weapons belong to the older stage of Post-tertiary 

 time (Pleistocene) known also as the Palaeolithic or ancient stone 

 period, to distinguish it from the Neolithic, or new stone period. The 

 more recent of these periods, however, may be divided into an 

 older and a newer stage, indicating an advance in culture, as illus- 

 trated by the relics found on the shores of the Danish islands. 



V. — The Eocks of St. Davids. 

 By Henry Hicks, M.D., F.R.S., F.G.S. 



IN a characteristic article by Prof. Blake, "On the Base of the 

 Sedimentary Series in England and Wales," in the July Number 

 of the Geological Magazine, amongst other erroneous statements, 

 there is one which I must beg leave to correct. At page 310, in 

 referring to the rocks of St. Davids, he makes the following state- 

 ment : "While accepting the later petrological descriptions of Dr. 

 Hicks, he (Dr. Geikie) minimized the separation between this [the 

 Pebidian] and the Cambrian conglomerate, and challenged Dr. 

 Hicks to prove his statement that the latter is chiefly composed of 

 fragments of the rock on which it lies. This Dr. Hicks has never 

 been able to do, seeing that the most marked feature of the con- 

 glomerate is that it is not composed of such fragments ; instead of 

 doing so, he now attempts to show that the matrix might have been 

 derived from granitoid rocks." 



One would never have supposed that any geologist who had made 

 even a most imperfect examination of the district, and had but a 

 slight acquaintance with the literature of the subject, would have 

 ventured to make such a reckless assertion, especially after the pub- 

 lished notes by such eminent petrologists as Prof. Bonney and Mr. 

 Davies in the Q.J.G.S. vols. xl. and xlii., which give abundant 

 examples to show that the Cambrian conglomerates contain fragments 

 identical with the rocks underlying them. Moreover, at Kamsay 

 Island, Trefgarn, and elsewhere, three-fourths of the pebbles in the 

 conglomerate must have been derived from the rocks immediately 

 below. In the Q.J.G.S. vol. xlii. p. 358, Prof. Bonney says, "The 

 sections contain numerous fragments of felspar, very similar to that 

 in the Dimetian ; in short, they present every appearance of an 

 'arkose' to which granitoid rocks have largely contributed. Six 

 out of the seven slides include well-marked fragments of granitoid 



rock In all respects the section of this fragment curiously 



resembles the slides of ' Dimetian ' rock." Again, at p. 362, he gives 

 the following as his conclusions : — 



DECADE III. VOL. VII. — NO. IX. 26 



