• Abstract and Figures
• Public Full-text

Downloaded from http://trned.lyellcollection.org/ at University of Georgia on June 18, 2015 332 EDINBURGH GEOLOGICAL SOCIETY. XLVIII. The Subdivisions of the Carboniferous Series in Great Britain and some of their European Equivalents. By WHEELTON HIND, M.D., B.S.Lond., F.E.C.S., F.G.S. (Read 20th January 1898.) IT is a well recognised fact " that the sequence of the Carboni­ ferous series of beds, as found in Scotland, differs essentially from that which obtains in central England," and the correlation of the two groups has been attended with difficulty, mainly due, as I have pointed out in the Geological Magazine for April and May 1897, to a misconception of the succession of carboni­ ferous rocks in Yorkshire, and to the fact that Professor Phillips established a purely local succession as typical of the carboni­ ferous sequence in central England. The main evil-which has resulted from this classification, is that in other districts where the succession is totally different, an altogether artificial and arbitrary set of divisions has been made, which can neither be followed in the field nor identified by palseontological evidence, so as to bring it into line with the so-called typical section. Several systems have been proposed for the classification of the carboniferous rocks, all more or less based on lithological characters, for, up to the present, little or nothing has been accomplished in establishing life zones for the carboniferous rocks of Great Britain ; but the great mistake in all of them is the establishment of the millstone grit and Yoredale series as essential subdivisions, and the attempt to make artificial equivalents for them in Scotland and Ireland, where the succession of rocks is often entirely different from that which obtains in central England. Would the terms millstone grit and Yoredale series ever have arisen if the carboniferous succession in Scotland had been chosen as the type ? I would emphatically protest that these so-called subdivisions are only extremely local conditions, and due to local causes, which prob­ ably were not acting in other districts, and I propose to show that such is the case by tracing the sequence of the carboni­ ferous beds from Derbyshire to Scotland and noting the gradual series of changes which they undergo in passing from the English to the Scotch type of succession. In Derbyshire we have not yet been able to reach the base of the carboniferous limestone, which exists as practically one mass, for though composed of various beds—crinoidal, detrital, Downloaded from http://trned.lyellcollection.org/ at University of Georgia on June 18, 2015 SUBDIVISIONS OF CARBONIFEROUS SERIES IN GREAT BRITAIN. 333 siliceous, organic—the limestone is not divided up, as in Scotland, into beds by masses of shales; and we only find thin partings of 1 to 6 inches at rare intervals. Lower Limestone Shale, Basement Beds, etc.—Although not exposed, we have every reason to believe that beds of Carboni­ ferous age may exist below the limestone, for such a bed is known to be 660 feet thick in the Avon section, near Bristol, and in North Wales the basement beds, consisting of bastard limestone, conglomerates, and shales, etc., with pebbles con­ taining Silurian fossils, reach about 500 feet. In the Pennine area, the basement beds are only exposed at the foot of Ingleboro, in King's dale and Eibblesdale. Here the beds are very thin and patchy, resting unconformably on the upturned edges of Silurian slates, and at Thornton Force only attain to about 5 feet in thickness. Here the beds consist of a brecciated conglomerate with quartz pebbles and rolled Silurian rocks and occasional carboniferous corals. Further north, Mr Good- child has described the basement beds in Hebblethwaite gill; and these are succeeded by about 130 feet of shales and impure limestones which occur immediately below the great Scar lime­ stone. The following section of these beds is given by the Geological Survey (Mem. Geol, Mallerstang, p. 50):— Feet. J Grey calcareous sandstone with green partings and white nodules 40 Bed and green shale with hard sandy bands and numerous con­ cretionary white nodules at the top 12 Lower limestone Purple and white mottled sandstone 3-4 shales and base- / Bed conglomerate.... 3 ment beds. 1 Bed sandstone .... 2-4 Bed conglomerate..... 20 Conglomeratic grey and purple sandstones with bands of red conglomerate interstratified . 17 Bed conglomerate of Hebblethwaite ^ gill estimated at about . 900 Some of these beds are seen again in Eavenstonedale, but the basement conglomerates are not seen and are probably absent. In the neighbourhood of Ash Fell and Boman Fell, Mr Goodchild has drawn attention to the presence of an interesting series of sandstones with plant remains, limestones of tolerable thickness, conglomerates and shales which is developed below the great Scar limestone. Further north still this series VOL. VII. PART IV. Z Downloaded from http://trned.lyellcollection.org/ at University of Georgia on June 18, 2015 334 EDINBURGH GEOLOGICAL SOCIETY. expands into the Tuedian beds of Northumberland, which are subdivided by the officers of the Geological Survey into lower freestones, cement limestones, and an upper set of Fell sandstones. The lower group, also consisting of two divisions, thus:— j , [ With freestones, dark-grey and greenish UpperT or cement , , .' f s « 6 , stone ou 1 s^ales W1^^ impure bands ot limeston v e [ and cement stone. Lower. Freestone f Freestones with purple, lilac, green and group. \ red shales. At the base of the latter occurs occasionally a pebbly base­ ment bed, and in some places a conglomerate. The upper division or Fell sandstones consist of thick beds of quartzose sandstone of various colours with beds of shale, sometimes marine. The fauna of the Tuedian beds is largely non-marine, and is characterised by the presence of Modiola Macadamii, but it differs markedly from the fauna in the beds above, called The Carboniferous Limestone Series, which contains Productus giganteus at several horizons, a fossil never found in the Tuedian or calciferous sandstone series. I regard these Tuedian beds as the Homotaxial representatives of the basement beds of Ingleboro and the Calciferous Sandstone Series of Scotland. In the field there is abundant evidence that deposits which are the results of land denudation increase in thickness and importance as they pass northwards, where there is no doubt the continent existed whence they were derived. On the Fifeshire coast Mr Kirkby has shown that these beds contain occasional marine bands, and if the fauna of the bands and that which the officers of the Survey have found in the Tuedian beds be compared they will be found to be very similar. Carboniferous Limestone Series.—In the Mendips, Derbyshire, and the south of Yorkshire the Carboniferous Limestone is in one mass, made up, it is true, of various beds, encrinital, detrital, etc., but the beds are not separated from each other by any extent of shales. Occasionally in Derbyshire thin partings may occur which rarely attain a thickness of 6 inches. Between Castleton in Derbyshire and Clitheroe in S.E. Lanca­ shire the limestone is not exposed, but as far north as this, it still maintains the same massive structure as further south. The uppermost beds in Derbyshire are highly fossiliferous and are largely made up of well rolled shells and fossil fragments, with pebbles of hard limestone and an occasional one of white quartz. This bed was evidently laid down between tidal limits and I have been able to trace it for miles across country, always Downloaded from http://trned.lyellcollection.org/ at University of Georgia on June 18, 2015 SUBDIVISIONS OF CARBONIFEROUS SERIES IN GREAT BRITAIN. 335 at. the same horizon, where it marks the line of a retreating sea-beach. This condition of things also occurs in the neighbourhood of Grassington at Hill Bolton and the series of several dome- shaped limestone hills, a characteristic form of weathering both in Yorkshire and Derbyshire, but here the shells afford less evidence of rolling. It was these dome-shaped hills and the shell beds in them which were remarked upon by Mr Tiddeman in a paper read before the British Association, 1890, and pub­ lished at p. 600 of the Beport. He speaks of the hills "as suggestive of the idea of reef-knowls," which he speaks of as " growing up on a slowly sinking sea bottom "; and goes on to say: " Moreover, at the foot of these mounds or reef-knowls, as I would call.them, we have in many places a breccia formed of fragments of the limestone, which, I take it, have been broken off the reef between wind and water and have subsequently been covered up by the mud of the Bowlancl shales and compacted into a breccia." Now in the first place there are no reef-build­ ing Corals in the Carboniferous Bocks and no other organism which is capable of constructing reefs, so that this theory falls to the. ground at once ; but further, the peculiar conformation of the country at that place is due to the natural weathering of a rock soluble in water, and the same shaped knolls of weathered limestone occur frequently in Derbyshire, N. Staffordshire, the Isle of Man, and notably in the upper beds of limestone north of Malham Cove. In fact, the breccia of limestone and rolled fragments is the contemporaneous beach which occurs, just as it does in Derby­ shire, at the top of the limestone, and is overlaid by the Bowland shales. Of all the wild speculations of geologists, this, I think, is based on as little actual fact as any, and Mr Tiddeman cuts the ground from beneath his feet when he adds as a postcript: " In speaking of the mounds as knowl-reefs, I do not neces­ sarily wish to imply that they were coral reefs.

Load more

  29

Copy Link