Societies and Academies

    Article metrics


    LONDON: Geological Society, November 8.-Prof. P. Martin Dunca'n, F. R.S., president, in the chair.-Melville Attwood, San Francisco, and R. W. Moore, Whitehaven, were elected Fellows of the Society.-The following communications were read:-A short notice of a new exposure of rhostics near Nottingham, in a letter from E. Wihon, F.G.S., dated November 3, 1876.-Note on the Red Crag, by W. Whitaker, F.G.S.-On the Kessing-land Cliff Section, and the relation of the forest-bed to the Chillesfcrd Clay, with some remarks on the so-called terrestrial surface at the base of the Norwich Crag, by F. W. Harmer, F.G.S.-Observations on the geology of East Anglia, &c., by S. V. Wood, jun., F.GS., and F. W. Harmer, F.G.S., &c. The subjects discussed in this paper were threefold, viz.:-(i) The unfosdliferous sands of the Red Crag. (2) The uriconformity between the Lower and Middle Glacial deposits. (3) The mode in which the Upper and Middle Glacial were accumulated. The views of the authors unr'er the first head were similar to and confirmatory of those advanced in the previous paper by Mr. Whitaker; but they pointed out that the Red Crag, which these sands, in an altered form, represent, could not belong to the Chillesford division of that formation, by reason of the casts of shells which had been preserved not comprising any of the more characteristic Chillesford species, and of their including among them forms confined to the older portions of the Red Crag. They also pointed out that the Chillesford Clay had been removed over all the area occupied by these sands by denudation prior to the deposition of the Middle Glacial, which rests upon these sands wherever they occur. The removal of the Chillesford Clay, the authors consider, was due in part, if not in all, to the great denudation between the Lower and Middle Glacial, which gave rise to the unconformity discussed under the second head. This unconformity they illustrate by lines of section traversing most of the river valleys of Central and East Norfolk and Suffolk. These show that such valleys were excavated after the deposit of the Contorted Drift, and out of that formation and the beds underlying it. They also show that the Middle and Upper Glacial have been bedded into these valleys, as well as spread (the middle only partially, but the upper more uniformly) over the high grounds formed of contorted drift out of which they were excavated, and thus generally concealing that deposit, which manifests itself only in the form of occasional protrusions through these later formations, but which they consider constitutes, though thus concealed, the main mass of the two counties. The authors also describe a glacial bed as occurring at various localities in the bottom of some of these valleys, and which in one case they have traced under the Middle Glacial. This they regard as having been formed in the interval between the denudation of the valleys and their subsequent submergence beneath the Middle Glacial sea; and inasmuch as such valley-bed invariably rests on the chalk in a highly glaciated condition, they attribute its formation more probably than otherwise to the action of glaciers occupying the valleys during an inter-glacial interval of dry land. They also suggest that if this was so it is probable that that the forest and mammaliferous bed of Kessingland, instead of being coeval with the pre-glacial one of the Cromer coast, may belong to this inter-glacial interval- that is to say, to the earliest part of it, before the glaciers accumulated in the valleys, and when the climate was more temperate, any similar deposits in these inter-glacial valleys having been for the most part subsequently ploughed out by the action of the glaciers. In discussing the subject, under the third head the authors point out the many perplexing features which are connected with the position and distribution of the Middle Glacial formation; and while they admit that as to one or two of these the theory which they offer affords 'no explanation, they suggest that the theory of this formation's origin which best meets the case is as follows, viz.:-As the country became re-submerged, and as the valley glaciers retreated before the advancing sea, the land-ice of the mountain districts of North Britain accumulated and descended into the low grounds, so that by the time East Anglia had become re-submerged to the extent of between 300 and 400 feet, one branch of this ice had reached the borders of the counties of Norfolk, Suffolk, Essex, Herts, and Bedford, ploughing out and destroying any lower glacial beds that had been deposited over the intervening counties upon which it rested, and over which we ought otherwise, having regard to the depth of the earlier submergence under which they were accumulated, to find them, but do not. The Middle Glacial formation, consisting of sand and gravel, they attribute principally to the action of currents washing out and distributing the morainic material, which was extruded on the sea-bottom by this land-ice; that ice itself, by keeping out the sea over all the country on which it rested, which was then below the sea-level, preventing the deposit of the Middle Glacial in those parts. The termination of this current action was accompanied by increased submergence and by a gradual retreat of the land-ice northwards to the mountain districts, until Britain was left in the condition of a snow-capped archipelago, from which eventually the snow disappeared and the land emerged. To the moraine extruded from the base of this ice and into deep water they refer the origin of the Upper Glacial Clay, the moraine material remaining partly in the posi-lioii in which the ice left it, and partly lifted by the bergs which became detached from the ice. Such part of it as wasTifted was dropped over the sea-bottom, at no great distance from its point of extrusion, and ia that way the marine shells occurring in a seam of sand m the midst of this clay at Dimlington and 1'ridlingtcn on the Yorkshire coast became imbedded, the mol-iusca which had established themselves on the surface of this n oraine material having been thus smothered under a lifted mass of the same, which was dropped from a berg. The authors point out that precisely in the same way in which the Middle Glacial is found stretching out southwards and eastwards beyond the Upper Glacial Clay in Suffolk and in Herts, and is succeeded by such clay both vertically and horizontally, so does the earlier-formed part of the Upper Glacial Clay, or that with chalk débris, stietch southwards beyond the later-formed part, or that destitute of such débris and is succeeded by it, both vertically and horizontally. This, they consider, shows that the Middle and Upper Glacial deposits, which constitute an unbroken succession, were due to the gradually receding position of the land-ice during their accumulation, the sequence being terminated with the Moel Tryfaen and Macclesfield Gravels, which were accumulated during the disconnection and gradual disappearance of the ice, and while the land still continued deeply submerged.

    Rights and permissions

    Reprints and Permissions

    About this article

    Cite this article

    Societies and Academies . Nature 15, 130–132 (1876) doi:10.1038/015130b0

    Download citation


    By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.