478 



NATURE 



[September 15, 1898 



The latter is most likely to be the case.^ The vale of Pewsey 

 has been mentioned as a suitable locality for boring along the 

 line of the recognised axis. 



But prospectors should bear in mind the warning of Ramsay, 

 that the basins containing coal are but few in comparison with 

 the number of basins throughout the palceozoic rocks. No doubt 

 the line indicated is more favourably situated for coal-explor- 

 ation than the eastern counties ; where, for instance, the Coal 

 Boring and Development Company has lately gone into liquid- 

 ation. The unsuitability of East Anglia as a field for coal- 

 prospecting was insisted on in my second anniversary address 

 to the Geological Society ( ^;<ar/. yi7Mr«. Geol. Soc. vol. i., 1894, 

 p. 70), and the results seem to have been very much what might 

 have been expected. If coal is to be found beneath the 

 Secondary rocks, the line of search should be carried through 

 the counties of Kent, Surrey, Berkshire, and Wiltshire, though 

 the three latter counties have hitherto been content to leave 

 their underground riches unexplored. The Kent Coal Explor- 

 ation Company is doing some good work with a reasonable 

 chance of success ; though if they wish to find coal sufficiently 

 near the surface they had better adhere as much as possible to 

 the line of the North Downs, since operations on the Sussex 

 •side are only too likely to be within the influence of the Kim- 

 meridgian gulf, which was proved to exist at Battle (Nether- 

 field). Mr. Etheridge, I hope, will have something to tell us 

 as to the progress of the Kent Collieries Corporation, who now 

 carry on the work at Dover. 



Secondary or Mesozoic Rocks. — Commencing a totally different 

 subject, I must now direct attention to the "red beds " and 

 associated breccias so characteristic of eastern Devonshire. 

 These rest in complete discordance on the flanks of the 

 palaeozoic highlands, and must be regarded as forming the 

 base of the Secondary rocks of that district. 



By the Geological Survey this series has hitherto been mapped 

 as Trias, but in the new "Index -map" they are coloured as 

 Permian. There is no Palseontological evidence which would 

 connect them with the fossiliferous Permians, usually regarded 

 as of Palreozoic age, but it has been evident for some time past 

 that opinion was inclining to revert to the views of Murchison 

 and the older geologists, more especially as to the position of 

 the breccias so largely charged with volcanic rocks. The sub- 

 ject was dealt with by Sir A. Geikie in his address to the 

 Geological Society, where he speaks of some of these rocks as 

 presenting the closest resemblance to those of the Permian 

 basins of Ayrshire and Nithsdale {Quart, lourtt. Geol. Soc, 

 vol. xlviii., 1892, p. 161). 



One difficulty which presented itself to the Devonshire 

 geologists in accepting the Permian age of the "red beds" was, 

 that the whole of the lower Secondary rocks appeared as an 

 indivisible sequence, proved by its fossils to be of Keuper age at 

 ■one end, and therefore inferentially of Keuper age at the other. 

 Dr. Irving, however, considered that at the base of the Budleigh 

 Salterton pebble-bed there is a physical break of as much 

 significance as that between the Permian and Trias of the 

 Midlands. In the marls which underlie this pebble-bed he 

 recognised a strong resemblance to the Permian marls of 

 Warwickshire and Nottinghamshire ; and Prof. Hull, who had 

 been studying the sections east of Exmouth about the same 

 time, ultimately acceded to this view.^ Its acceptance by 

 the Survey thus throws all the Exmouth beds into the 

 Permian ; and that formation, according to the new reading, 

 has an outcrop of some thirty-five miles from the shores of 

 the English Channel to within three miles of Bridgewater Bay. 

 The fertility of these red clays, loams, and marls has long been 

 recognised by agriculturists, and it is not improbable that the 

 abundance of contemporaneous volcanic material may in some 

 measure have contributed to this result. 



In conformity with the new mapping, the Budleigh Salterton 

 pebble-bed and its equivalents to the northwards are accepted 

 as of Bunter age, and thus constitute the base of the Trias in 

 the south-west. Like most pebble-beds, they are irregularly 

 developed between the Permians and a strip of reddish sand- 

 stone (coloured as Keuper), which runs up from the mouth of 



1 The boring at Burford, where coal was found at a depth of 1 100 feet, 

 below a surface of Bathonian beds, at a point thirty-five miles E.N.E. of 

 ihe extreme endof the Bristol Coal-field at Wickwar, is not included in 

 this category ; since it must belong to the meridional system, and is alto- 

 gether outside the prolongation of the axis of Artois. 



■^ (Cf. Irving, Quart, /ortm. Geol. Soc, vols, xliv., 1888, p. 145, xlviii., 

 1892, p. 68, and xlix., 1893, p. 79; and Hull, op. cit. vol. xlviii., 1892, 



6o)- 



NO. 1507, VOL. 58] 



the Otter to within a short distance of Bridgewater Bay. The 

 materials of the pebble-beds are not of local origin, like so much 

 of the breccia at the base of the Permian. The general resem- 

 blance, both as regards scenery and composition, to the Bunter 

 conglomerate of Cannock Chase has been pointed out by Prof. 

 Bonney, who seems prepared to endorse the recognition of the 

 Budleigh Salterton pebble-bed as a Bunter conglomerate. He 

 was not impressed by any marked unconformity with the under- 

 lying series. To some extent we may accept this view, since 

 whatever may be the age of the Devonshire breccias and " red 

 beds," they, in common with the Trias, must have been deposited 

 under fairly similar physical conditions in a sort of Permo- 

 Triassic lake basin. 



The bulk of the Trias, including the Dolomitic Conglomerate 

 of the Bristol district, is still regarded as of Keuper age, though 

 it is now admitted, as insisted on by Mr. Sanders years ago, that 

 the Dolomitic Conglomerate does not necessarily occupy the 

 base of the Keuper, but is mainly a deposit of hill-talus, which 

 has been incorporated with the finer deposits of the old Triassic 

 lake as the several palaeozoic islands gradually became sub- 

 merged. The great blocks which fell from the old cliffs were 

 formerly regarded as proofs of glacial agency, and there are 

 persons who still believe, more especially with respect to the 

 Permian breccias, that such rocks are indicative of a glacial 

 origin. 



In the "Index-map" the Dolomitic Conglomerate and the Red 

 Marl are thus included under the same symbol and colour. But 

 this is also made to include the Rhslic — an arrangement which 

 is hardly in accordance with the facts observed in the Bristol 

 area. On a small-scale map so narrow an outcrop as that of the 

 Rhsetic could hardly be shown ; yet its affinities are probably 

 with the Lower Lias rather than with the Trias. The late 

 Edward Wilson, whose recent death we all deplore, in his paper 

 on the Rheetic rocks at Totterdown {Quart. Journ, Geol. Soc, 

 vol. xlvii., 1 89 1, p. 545), showed most clearly that the " Tea- 

 green Marls," which had previously been associated with the 

 Rhaetic, represent an upwards extension of the Red Marls of the 

 Trias, in which the iron had suffered reduction ; though there 

 are indications of a change of conditions having set in before 

 the deposition of the Rhaetics. The black Rhsetic shales which 

 succeed usually have a sharp and well-defined base in a bone- 

 bed with quartz pebbles, &c., indicating a sudden change of 

 physical conditions, though perhaps no marked unconformity. 

 In the South Wales district the Rhaetic limestones are said to 

 be largely of organic origin, and, in addition to a Rhsetic fauna, 

 to abound in the lamellibranchs so plentiful in the lowest Lias 

 limestones {Ann. Rep. Geol. Survey for 1896, p. 67). 



The late Charles Moore always deplored the comparative 

 poverty of the Trias in fossils. In his last communication to 

 the Geological ?>oc\eiy {Quart. Journ. Geol. Soc, vol. xxxvii., 

 1881, p. 67), he set himself to describe certain abnormal de- 

 posits about Bristol, and to institute a comparison with the 

 region of the Mendips. He then suggested, on the faith of a 

 sketch by Mr. Sanders, that the famous Durdham Down deposit, 

 already inaccessible, might have been a fissure-deposit in the 

 Carboniferous Limestone like those at Holwell. He also stated 

 that at one time he had been inclined to regard the reptilian 

 deposit on Durdham Down as of Rhaetic age ; but the discovery 

 of teeth of Thecodontosaurus, identical with those of Bristol, in 

 a Keuper Marl deposit near Taunton, induced him to refer the 

 Durdham Down deposit to the middle of the Upper Keuper. 

 He had arrived at the conclusion that the same genera of 

 vertebrata are found in the Keuper and Rh^tic beds, though the 

 species, with few exceptions, are quite distinct. 



But it is with the Lias that the name of Charles Moore is 

 most intimately associated. Time does not permit me to do 

 more than allude to the wonderful collections of Rhaetic and 

 Liassic fossils made by him from the fissure-veins of the Carbon- 

 iferous Limestone, or of the treasures which are stored in the 

 Bath Museum. There never was a more enthusiastic palae- 

 ontologist, and nothing pleased him better than to exhibit the 

 fossilised stomach of an Ichthyosaurus, stained by the ink bag 

 of the cuttle-fish, on which it had been feeding, or some similar 

 palaeontological curiosity. Every one here knows how deeply 

 the West of England is indebted to Charles Moore for his 

 unceasing researches, and I have been thus particular in alluding 

 to them because it was under his auspices that I first became 

 acquainted with the geology of this part of the country thirty 

 years ago. 



Amongst more recent work in the Rhaetic and Lias, I might 



