TKANSACTIONS OF SECTION C. 613 



great beds of breccia, so finely exposed on the South Devon coast, are crowded 

 with fragments, sometimes of large size ; these have clearly been derived from the 

 older rocks which are stiU in part exposed to the west and south-west, and probably 

 had once a much greater extension in the latter direction. Fragments of Devonian 

 limestone, grits, and slate, together probably with other Palseozoic rocks, earlier 

 and later, are mingled with granites, resembling those of Cornwall and Devon, 

 and many varieties of more compact igneous rock. The fossiliferous quartzite 

 pebbles which occur mingled with others in the Trias at Budleigh Salterton, have 

 been discussed by the late Dr. Davidson in an exhaustive memoir.' He refers the 

 majority of the fossils obtained from them to the Lower Devonian age, but a few 

 are Caradoc, and four occiu* in France in beds which are either Llandeilo or 

 perhaps a little older. As the first two formations are represented, lithologically 

 and palfeontologically, on the opposite side of the Channel in France, and the 

 third is at present only known to occur in the Gres Armoricain of that country, he 

 thinks it probable that these pebbles have been derived from rocks which are now 

 concealed beneath the waters of the Channel. It may then, I think, be taken for 

 granted that laud to the west and south-west has supplied the materials of the 

 Lower Trias of the southern district of England, and I may add that there is every 

 reason to believe that outliers of the formation itself still exist beneath the sea. 



The so-called dolomitic conglomerates, which occur chiefly in Somersetshire, have 

 been so fully worked out by INIi". Etheridge and Mr. Ussher as to require but a passing 

 notice. It is evident that they differ somewhat in date, though probably all may 

 be referred to the age of the Keuper, and that they are local breccias or con- 

 glomerates formed around the margin of islands or on a continental coast-line during 

 a gradual subsidence and in comparatively quiet waters. 



Jurassic. — Coarse detrital material is not very common in the Jurassic series. 

 The limited Rhsetic beds indicate a transition from the peculiar physical conditions 

 of the Keuper to the marine conditions of the Lias, and the sediment in them was 

 probably derived from the same source as the Keuper marls. Great clay beds also 

 occur, as is well known, throughout the Jurassic series ; and the sandstones, so far 

 as I have been able to examine them, do not enable me to ofter any suggestions as 

 to their origin. Probably some of the grains were originally derived from 

 granitoid rocks, but they may have been directly obtained from other sandstones. 

 A grit, however, in the estuarine series of the lower oolites of Yorkshire (Mr. 

 PhUipps's collection) looks as if it might have been partly derived from a schist, but 

 as this is the only rock from the northern area which I have had the opportunity ' 

 of minutely examining, it would be imprudent to speculate. 



Neocomian- Cretaceous. — I have examined very few specimens from the fresh- 

 water Neocomians of the South of England, but, so far as I have seen, I should 

 think it probable that the quartz had been derived from old crystalline rocks, 

 though perhaps not immediately. The same remark applies to the sands of the 

 upper and marine series, which, in one instance at least, exhibit exceptionally 

 rounded contours.'- Among these, however, conglomeratic beds occur which 

 have already attracted some attention. It is obvious that no small part of the 

 materials, as at Farringdon, Potton, and Upware, has been derived from fossiliferous 

 secondary rocks of earlier date. There are also pebbles of vein-quartz and quartzite 

 which, however, may have been obtained by the denudation of Triassic rocks. The 

 * Lydian stone,' which is abundant in angular or subangular fragments at Potton 

 and Upware, is for the most part chert from the Carboniferous Limestone, or in 

 some cases from Jurassic rocks, but a few specimens may be flinty argillites, and thus 

 of greater antiquity. One or two pebbles of older Palaeozoic rock have been found, 

 and a hard quartz grit has occiu-red, containing among its grains minute acicular 

 crystals, probably of tourmaline. Potton has furnished one or two pebbles which 

 appear to be a devitrified pitchstone, and a large pebble of porphyritic quartz- 

 felsite has been sent to me by Mr, Willet from Henfield (Sussex). These conglo- 



' ' British Fossil Brachiopoda ' (Mem. Palteont. Soc. vol. iv. p. 317). 

 - Professor Eupert Jones has called attention to sand-worn pebbles in the Upper 

 Tunbridge Wells sandstone of the Weald (Geol. Mag. Dec. 2, vol. v. p. 287). 



