Wales, Gloucestershire, and Somerset, and also to some portion of the higher part of the old red sandstone of Herefordshire and adjacent districts."* Professor Haughton, still more heretical, says, "I do not believe in the lapse of a long interval of time between the Silurian and Carboniferous deposits-in fact, in a Devonian period. The same blending of corals has been found in Ireland, the Bas Boulonnais, and in Devonshire, where Silurian and Carboniferous forms are of common occurrence in the same localities."t The truth of this assertion is, perhaps, more than doubtful. It is known that the eminent authorities, Mr. Lonsdale and M. Milne Edwards, differ somewhat widely respecting our fossil corals; they agree, however, that there is not a single Carboniferous coral in our Devonshire rocks. In 1862, I ventured into this discussion, and stated, on palæontological evidence, that "there are in Devon and Cornwall no representatives of the Lower and Middle Old Red rocks of Scotland, but that the Lowest beds of the former are on the horizon of the Upper division of the latter."t The following is very briefly the evidence on which this opinion was based: Of the 347 supposed species of invertebrata then found in both North and South Devon and in Cornwall, 8 were believed to belong also to the Silurian system, and 58 to the Carboniferous; hence the connexion of the Devonian with the latter was more intimate than with the former. In addition to this, I had recently found, between Meadfoot Sands and Hope's Nose, in Torbay, a scale of the fossil fish Phyllolepis concentricus-the only known Old Red ichthyolite yet met with south of the Bristol Channel. It occurred in the Lowest Slates of Devonshire-known to be so from the unquestionable test of superposition-where are also found specimens of the coral Pleurodictyum problematicum: that is, a fossil characteristic of Sir R. I. Murchison's Upper Old Red, in the same group with another fossil peculiar to his Lower Devonian. In accordance with the foregoing opinion, I suggested, in 1863, that the Old Red and Devonshire beds collectively, but not separately, fill the Siluro-Carboniferous interval; and that if this interval were, in consequence of established usage, to be still called the "Devonian period," it would be * Mem. Geol. Survey, vol. i., page 103. 1846. "Voyage of the For." Appendix, No. 4, page 387. convenient to divide it into sub-periods-the Old Red, or more ancient; and the Danmonian, or more modern. The succession being as in the following scheme:* In 1866, Mr. Page said, "We have examined the strata of Devonshire from north to south and from east to west, and instead of finding the equivalents of the Scottish Old Red we discovered in the Northern division one set of rocks that should be ranked with the lowermost Carboniferous, and in the Southern another that perhaps was contemporaneous with portions of the middle and upper Old Red. At all events, the rocks of Devonshire as a whole do not represent the Old Red Sandstone of Scotland, of Northern Europe, and North America as a whole."† Mr. Beete Jukes has recently brought forward a opinion, which, from his great experience as a geologist, and from his official position, has received a large amount of attention, and is not unlikely to attract still more, for authority has branded it as a heresy. In order to a clear idea of this opinion, it may be desirable to state that the Carbon Davidson's "Devonian Brachiopoda," Pal. Soc., pages 44, 45. 1864. The following are further localities in Devon and Cornwall: (a) Baggy Point, Pilton, Tintagel, &c. (6) Ilfracombe, Barton, Woolborough, Hope's Nose, Babbacombe, Dartington, Berry Head, Plymouth, and other limestone districts. (e) Mudstone, Linton, Looe, Polperro, Fowey. + "Geology for General Readers," page 93. 1866. iferous system of deposits is frequently divided into three groups: : The Upper, or Coal Measures. The Middle, or Carboniferous Limestones. The Lower, or Carboniferous Slates. The Slates are well developed in the south-west of Ireland, where, Mr. Jukes thinks, the readiest solution of the problem of Devonshire is to be found. He contends that "the Carboniferous Slate is absolutely contemporaneous with the Carboniferous Limestone."* He admits that where, in the South-west of Ireland, "the Carboniferous Slate and Carboniferous Limestone are both present together, the Carboniferous Limestone is uppermost; but that where the Carboniferous Limestone has a thickness of 2000 feet or upwards, the dark slates between it and the Old Red Sandstone are very thin, rarely more than 200 feet in thickness; while, where these dark slates thicken out to more than 2000 feet, there is no great thickness of Carboniferous Limestone over them. Where the Carboniferous Slate attains a still greater thickness, and swells out to three, four, or five thousand feet, it has never any Carboniferous Limestone over it at all; but there appear here and there patches of black slate upon it, which, both lithologically and palæontologically, resemble the Coal-measures. If so, the Carboniferous Slate occupies, there, the whole interval between the top of the Old Red Sandstone and the base of the Coal-measures, with a perfectly conformable and continuous series of beds to the exclusion of the Carboniferous Limestone. Dark grey mud and sand were at first deposited over the whole area, but were subsequently restricted to a part of it, where they continued to be deposited in great quantity; while in the rest of the area clear water prevailed, in which limestone was formed from the Crinoids and other animals that flourished in that part." Mr. Jukes has carried on his studies of the Devonshire rocks almost exclusively in the northern division of our county. In his paper, read in August, 1866, he says, "As I shall have to maintain that all the first geologists of the day, including Professor Sedgwick, Sir R. I. Murchison, Mr. Weaver, Sir H. De la Beche, and Professor Phillips, have misunderstood the structure of the country, let me hasten to avow my belief that nobody, whose observations were confined to Devon and Somerset, could have arrived at any other "Notes for a Comparison between the Rocks of the South-west of Ireland and those of North Devon," p. 5. 1865. + Quar. Journ. Geol. Soc., vol. xxii., pages 344-5. 1866. than their conclusions. I fully admit that the rocks near Lynton appear to be the lowest, and that there appears to be a regular ascending succession of rocks from Lynton to the latitude of Barnstaple. I am, however, compelled to dispute the reality of this apparent order of succession, and to suppose that there is either a concealed anticlinal, with an inversion to the north, or, what I believe to be much more probable, a concealed fault running nearly east and west through the centre of North Devon, with a large downthrow to the north, and that the Lynton beds are on the same general horizon as those of Baggy Point and Marwood."* After giving minute petralogical, lithological, and palæontological details respecting the deposits under consideration, in various localities in this and the adjacent county, Mr. Jukes says, "The following are the conclusions, respecting the Paleozoic rocks of North Devon and West Somerset, to which my previous experience in Ireland has led me:— There are three areas of Old Red Sandstone 1st. (a) "The Quantock Hills. (b) "The Porlock, Minehead, and Dunster area. (c) "The Morte Bay and Wiveliscombe ridge. The These have an irregular anticlinal form. Quantock Hills anticlinal is partly concealed on the western flank. . . . . . The Porlock, Minehead, and Dunster anticlinal has its south-eastern termination tolerably well shown in Croydon Hill, but is obscured on the North and North-east. .. The Morte Bay and Wiveliscombe anticlinal has its northern arm broken down by a great longitudinal fault running along its crest. 2nd. "Each of these three areas of Old Red Sandstone dips under a great mass of Carboniferous Slate. . . . . . The Carboniferous Slate of the two northern areas, that spreading S.E. from the Quantock Hills, and that stretching through Exmoor Forest to Morte Point, is thrown into numerous undulations, and thus spreads over wider spaces than it would otherwise occupy. The beds of the southern area, running from the country south of Wiveliscombe to Baggy Point, have a much more steady strike, and dip at a higher angle to the south, ... and therefore soon become covered by the Coal-measures. 3rd. "These three groups-the Coal-measures, the Carboniferous Slate, and the Old Red Sandstone to the south of the Bristol Channel, are contemporaneous with the three * Quar. Journ. Geol. Soc., vol. xxii., p. 321. 1866. groups-the Coal-measures, the Carboniferous Limestone, and the Old Red Sandstone to the north of the Bristol Channel." So far as it affects our own county, this new doctrine, on which I have dwelt at some length, amounts to this: The rocks at the Foreland Point are Old Red Sandstones, having over them Carboniferous Slates, which, with numerous undulations, are continued from Lynton to near the central shores of Morte Bay. Here there occurs a gigantic fault running a little south of east to Wiveliscombe, and bringing to the surface, along that line, the Foreland Old Red Standstones, which, before reaching Baggy Point, are again overlaid with Carboniferous Slates. These Slates, in their turn, dip, at Barnstaple, southwards under the Carboniferous beds or Coal-measures. As previously stated, this unqualified disbelief of accepted opinions has called forth a reply. Mr. Etheridge, in April last (1867), read to the Geological Society a paper "On the Physical Structure of North Devon, and on the Palæontological Value of Devonian Fossils," in which "the Lower, Middle, and Upper groups of sandstones and shales were described as occurring in a regular and unbroken succession from north to south; namely, from the sandstones comprising the promontory of the Foreland at the base, to the grits and slates, etc., overlying the Upper Old Red Sandstone of Pickwell Down to the south. The author was unable to see any traces of a fault of sufficient magnitude to invert the order of succession, or that would cause the rocks of the Foreland at Lynton to be upon the same horizon as those south of a line of high ground that passes across the county from Morte Bay on the west, to Wiveliscombe on the east. Arguments were also brought forward to show the probability of the Carboniferous Slate (in part) . . . . being the equivalent of the English Upper Old Red Sandstone, or Upper Devonian, and that the North Devon beds only are to be regarded as the true type, to which the Irish must be compared, and not vice versa. The author compared the whole of the Devonian fauna of Britain with that of the Rhine, Belgium, and France, . . . . . . . . the result being the conclusion that the marine Devonian series, as a whole, constitutes an important and definite system."+ This contrariety of opinion manifested by two distinguished officers of the Geological Survey, very forcibly brings before * "Additional Notes on the Grouping of the Rocks of North Devon and West Somerset," pages 13, 14. 1867. + Geological Magazine, vol. iv., pp. 272-3. 1867. |