into a large round knob, further downward growth being prevented by this indurated formation. This oxide of iron also pervades the sandy soil, in parts, to a depth of four or five feet, impregnating the water with ferruginous properties, so that it “ferrs” bottles, or vessels, in which it is allowed to stand for any length of time. In consequence, the water frequently has a dull appearance, although the iron may probably make it a wholesome tonic.
The surface sand, which is of a still lighter character on the moor ground in Woodhall, and in Martin, Roughton, and Kirkby, contiguous to Woodhall, is what is technically called the “Old Blown Sand,” borne by the winds from the whilom salt marshflats of the Witham, when it was much wider than at present, and a tidal arm of the sea. It is comparatively a recent formation, yet abounding in fine particles, or pebbles, of quartz, and other elements of far earlier date; the larger of these are often rounded by tidal action. Below this surface sand we find, in many parts, a blue clay of varying depth. In a pit called Jordan’s pond, in an abandoned brickyard on the east of the road to Stixwould, it is at least 16ft. thick; also, in a large pit in Kirkstead, near Hogwood, some half-mile south-east of the Abbey Inn, which was dug to procure this clay, for “claying” the light super-soil, otherwise almost barren, it is many feet thick. Ammonites and other fossils are plentiful in it, often cemented together with veins of gypsum. Both these pits are mentioned in the Government Geological Survey (pp. 152, 153) of “The country around Lincoln.” Close by the latter pit the writer once found a curious fossil, which was for some time a puzzle to all who saw it. It is now in the British Museum, and was pronounced to be an Echinus crashed into an Ammonite.
The Kimeridge clay, named as the next stratum in the bore of the Woodhall well, crops up first about Halstead Hall in Stixwould, and continues through Woodhall to Horncastle, and so on to Wragby and Market Rasen. It abounds in fossils. Mr. Skertchly [92] found in the first of the pits just named, that this clay was divided into three layers, the upper being a line of Septaria (or nodules) full of serpulæ one foot in depth, then soft dark-blue clay, 6ft.; and below that another course of Septaria; and
Professor J. R. Blake records from this pit the following fossils[93a]:—Belemnites nitidus, Ammonites serratus, Rissoa mosensis, Avicula ædiligensis, Cyprina cyreneformis, Ostrea deltoides, Lima ædilignensis, Thracia depressa, Arca, Serpula tetragona. In other pits in the neighbourhood several other fossils have been found. [93b] [For a list of fossils found about Woodhall see Appendix II.] A peculiarity of this stratum is that the upper part of it contains bands of “inflammable shales,” being blue, laminated, bituminous clays, which burn readily. It was the presence of these which has tempted explorers to throw away their money in search of coal; as in the case at Donington on-Bain, where Mr. Bogg drove a bore to the depth of 309ft., but only found clay and thin bands of inflammable schist. [93c] In the case of Woodhall Spa, the money thrown away on one purpose has brought health and wealth to others, from a source then undreamt of in man’s philosophy. We cannot leave the Kimeridge clay without noting that its presence at Woodhall, in the position where it is, as the first geological formation below the surface drift, opens to us a vista—reveals to us a yawning hiatus—which embraces a vast expanse of time.
In the normal order of geological strata, the whole series of cretaceous formations have to be passed through before reaching the Oolite formation, of which the Kimeridge clay forms almost the upper layer. But at Woodhall and the surrounding district the whole of this series of rocks and soils is wanting. Their absence is eloquent, and tells a tale of widespread destruction. Standing near the Tower on the Moor we can see in the distance, stretching from north-west to south east, the range of hills called the “Wolds,” which, with a “cap” of marls, or sandy and flinty loams, are composed almost entirely of chalk; from them, near Cawkwell Hill (the hill par excellence of chalk), comes the water supply of Horncastle and Woodhall. They extend for a length of some 45 miles, with a width of some six miles to eight. The actual depth of the chalk is not exactly known, but a boring made through it, near Hull, reached the
Oolite beneath at 530ft. We may perhaps, therefore, put the average at 500ft. [94a] Doubtless, at one period, this cretaceous formation extended over the whole tract of country, but southward and westward from the foot of the present wolds it has since been swept away. And this must have taken place before the glacial period, because the glacial boulder clay lies upon the Kimeridge clay, which normally underlies the chalk. Mr. Jukes Brown (“Geological Journal,” No. 162, p. 117) says: “The Boulder clay is bedded against the slope of the chalk, shewing that this escarpment had retired to its present position in pre-glacial times.” By what precise process this was effected must be left to our savants to decide; but the remarkable fact remains, that a solid stratum, or rather series of allied strata, from 500ft. to 1,000ft. in thickness, has, by one process or another, been wiped out of existence, over the large area now coated by the Kimeridge clay. Through ages of enormous length the chalk was forming as the bed of a sea; a deposit consisting of inconceivable myriads of beautiful minute shells, mainly of the foraminifera, which can be detected by the microscope; and its destruction probably occupied as long a period as its formation.
Mr. Jukes Brown, whom I have just quoted, says: “The Wold hills must have been, in some way, exposed to a severe and long-continued detrition, when erosive agencies were very active.” Active, indeed, they must have been, to efface from an area so extensive a solid formation from 500ft. to 1,000ft. in thickness. And this boulder clay, as Mr. Jukes Brown further observes, has forced its way up the sides of the chalk, in places, to a height varying from 300ft. to 400ft.
The Oxford clay, which lies next below the Kimeridge, is a deep sea deposit, dark blue, with brown nodular stones; some of the fossils found in it are Nucula Ornata, Ammonites Plicatilis, A. Rotundus, Cucullæa, Gryphæa Dilatata, Leda Phillipsii, Annelida Tetragona, and A. Tricarinata, Avicula inequivalvis. [94b]
Kellaway’s rock, which lies just below, so called from a village in Wiltshire, near Chippenham, is a mixture of yellowish and buff sands, with brown and buff sandstone. The
chief fossils are Gryphæa Dilatata, and G. bilobata, Belemnites in abundance, and Avicula Braam-buriensis. [95a]