IV. Observations on some of the Strata between the Chalk and the Oxford Oolite, in the South-east of England. BY WILLIAM HENRY FITTON, M.D., F.R.S. P.G.S., &c. [Read June 15, 1827.] (1.) IN a paper published in the Annals of Philosophy for November and December 1824*, I gave an account of the order and characters of the strata which occur beneath the chalk on the coast of part of the Isle of Wight and of Dorsetshire, and stated some reasons for supposing that a similar arrangement would be found to exist in the interior of England. The principal objects of that paper were; First, to distinguish as a separate group, the series of strata now called the Lower Green-sand ;-which had previously been confounded either with the beds containing green particles immediately below the chalk, or with the sandy and ferruginous strata conspicuously exhibited on the coast at Hastings, and then called "Iron-sand." Secondly, to indicate more clearly than had been done before, the peculiar characters of the group, which succeeds in a descending order to that just mentioned, and is remarkably distinguished by its fossils from the strata immediately in apposition with it, both above and below. For this latter group, which includes the Weald clay, the sand of Hastings, and the Purbeck limestone, and is well entitled to a separate denomination, I have adopted the name of "Wealden," proposed by Mr. Martin, in his valuable memoir on the West of Sussext. (2.) The objects of the inquiries which have produced the following pages were, to compare some portions of the series of strata between the chalk and the Oxford oolite, in different parts of the South-east of England; to ascertain the existence of the Wealden in the interior; and, if possible, to determine its boundaries. * Annals of Philosophy; New Series, 1824, vol. viii. pp. 365, 458, &c. t "Memoir on a Part of Western Sussex": 4to, London, 1828. In stating the result of this investigation, I shall give a series of sections of the strata below the chalk, at places which I have myself examined*, beginning on the coast near Folkstone, and following the outline of the chalk thence to the sea on the N. West of Norfolk. The relative situation of these places is shown in the map annexed to this papert. The intermediate country, in general, I have not examined in detail, and some points of importance I have never seen; but those who may have opportunities of continuing the inquiry, will find, I hope, no difficulty in connecting their observations with mine. (3.) The series of strata about to be described extends from the Chalk down to the Oxford oolite or coral-rag, and is composed of alternating but irregularly distributed beds of Sand, Clay, and Stone. Among the sandy strata, it is important to discriminate not only between the Lower green-sand and that of Hastings, but to distinguish both from a third group, consisting principally of sand abounding in green particles, which lies beneath the Portland stone. Clay, of several varieties, occurs in all parts of this series; but three groups, constituting the Gault, the Weald-clay, and the Kimmeridge-clay, derive peculiar importance from their generally occupying valleys, or depressions, at the foot of the escarpments of the Chalk, the Lower green-sand, and the Portland stone, respectively, and thus producing conspicuous natural features in the tracts where this succession is observable. The stone of the tracts under consideration is either limestone; indurated sand-rock; chert; or siliceous matter intimately mixed with carbonate of lime, in the form of grit,-which has commonly a concretional structure, and seems to pass into continuous beds only by the approach and ultimate union of the concretions. But the most remarkable distinction, in the suite described in this paper, arises from the great difference of character in the organized remains which the principal groups include. The fossils of the chalk and green-sands and those of the Portland stone, are all marine, and the species numerous. But in the Wealden, between the lower green-sand and the Portland stone, although the fossils are abundant as to quantity, the species are comparatively few, and by far the greater part of them belongs to fresh water. The whole of the phenomena, in short, presented by this remarkable assemblage of beds, are such as to accord with the hypothesis of their having been deposited in fresh water communicating with the sea. * Plates X. a, and X. b. Plate IX. The detail, upon a larger scale, will appear in the new edition of Mr. Greenough's Geological Map of England. (4.) Combining these sources of distinction, the following arrangement and subdivisions may be adopted, the nomenclature of which, however exposed to criticism, is now probably too well established to be changed without inconvenience*. (5.) I proceed now to describe the Sections of these strata, beginning with the coast of Kent; and I shall connect with each section a list of such fossils as I have either found myself, or obtained on good authority from the places mentioned. The whole of the shells in these lists have been examined and named by Mr. James Sowerby, by whom also the drawings of the supposed new species were made, and the annexed engravings executedt. It is right to mention this explicitly, both that I may take the opportunity of expressing my acknowledgments for Mr. Sowerby's valuable and assiduous cooperation,— and that, being myself but very slightly acquainted with Conchology, I may place the portion of the following pages which relates to that subject on better authority than my own. Vicinity of FOLKSTONE, Kent. (6.) The small map, (Plate VII. fig. 1.,) reduced from the Ordnance Survey, represents the country in the immediate neighbourhood of Folkstone and ⚫ I have stated in another place (Annals of Philosophy, vol. viii. pp. 461, 462,) some objections to the employment of names for geological strata, which refer to characters not essentially connected with the structure or position of the objects to be designated. But the term green-sand, however faulty, besides the universal use of it in England, has been adopted both in Germany and France ;-where, however, it may be regarded, in some measure, as free from the disadvantages of a significant name. Sandgate, the relative position of this tract being shown on the general map, (Plate IX.). The View (Plate VIII.), for which I am indebted to the kindness of my friend the Rev. J. D. Glennie of Sandgate, shows the actual appearance of the coast from Eastware Bay to Hythe; and the section (Plate X a. No. 1.) illustrates the succession of the strata, on a part of the shore which is not distinctly visible in the more direct view from the sea. (7.) The chalk cliffs in the vicinity of Dover have been described in detail by the late Mr. William Phillips*; and the presence of the upper green-sand which had escaped the notice of Mr. Phillips, has been pointed out by Mr. De Basterott. These, with Mr. Conybeare's more general description ‡, and Mr. William Smith's coloured map of Kent, are the only modern geological illustrations of this part of England with which I am acquainted. But there is a publication of much earlier date,-Packe's "Chart of East Kent," with its explanatory memoir entitled AгKOгPAIA, printed in 1743, which, though not strictly geological in its immediate object, points out very correctly the connexion between the external features and the disposition of the strata in the tract to which it relates, and contains such excellent views in physical geography as to demand especial notice in this place§. (8.) As the chalk rises, in proceeding from Dover towards Folkstone, the upper beds disappear; the cliffs represented in the view and section consisting entirely of the lower members of that stratum. The rise of the marly chalk above the sea level occurs about a mile and a half to the east of the escarpment of Folkstone hill, and the place is well marked by the breaking out of a very copious and perennial spring, called "Lydden Spout," which issues from the top of these marly beds || ;- -a situation probably corresponding to that of the springs which everywhere appear in the interior, along the foot of the chalk range. Near the "Spout" the cliff is about 450 feet high; the upper part consisting of very white chalk, with a bed of flint nodules, the rest of chalk without flints, gradually assuming a greyer hue as it descends. About the middle of the cliff a thick bed has acquired by exposure a rough and darker surface, by the aid of which it can be traced towards the west; * Geol. Trans., First Series, vol. v. p. 16. Geol. Trans., Second Series, vol. ii. p. 334. § A more full account of this valuable work, which had been previously mentioned by Mr. Conybeare, will be found in a tract on the Progress of Geology in England, by the author of the present paper:-London and Edinburgh Philosophical Magazine for 1832, vol. i. p. 447, &c. A new species of Tornatella, named by Mr. Sowerby elongata, was found in the chalk marl at this place, by the Rev. G. E. Smith. See Plate XI. fig. 1. |