4. On the RHETIC BEDS near GAINSBOROUGH. Ar the Meeting of the British Association at Nottingham in 1866, I announced the discovery of the Rhætic beds at Lea (a village about two miles to the south of Gainsborough), which the lowering of the gradients of the Great Northern line from Gainsborough to Lincoln had laid bare. At the time this announcement was made, the cutting at Lea was only partially worked out. Now, however, that the line is in a more complete state, I am enabled to give more accurate sectional and stratigraphical details than I could then. The following is a section of the various beds in the order in which they occur. No. of bed. Section of the Rhætic Beds at Lea, near Gainsborough. Lithology. 02 1 6 0 0 1 0 0 2 1 0 2 0 1 5 8 Black fissile pyritous shale A. contorta, S. cloacinus, &c. 2 4 highly fossiliferous, with septarian nodules. 7 Hard fine-grained mica- A. contorta, teeth, scales, 06 Bones, teeth, scales, and 04 0 1 3 Bone-bed imbedded in a Coprolites, worn bones, small pebbles, scales, and A. contorta, S. cloacinus, co- A. contorta, portion of jaw 8 0 1 0 25 10 The first traces of this Rhætic tract, for it can boast of only a very limited surface-area, occur a little beyond the third bridge, about a mile and a quarter from the new station at the south end of the town of Gainsborough, where the lowest bed of the series, No. 1 in the section, is seen resting unconformably, though with parallel stratification, on the blue marl of the Keuper beneath. This bed consists of a rather loose micaceous sandstone of a greenish grey colour, containing a few specimens of Avicula contorta, with worn bones, teeth, and coprolites, and is (where not affected by the unevenness of the underlying Triassic marl, the hollows of which it fills up) on the average about a foot in thickness. In one part, near the outcrop of this lowest bed, lying directly on the blue marl beneath, I found part of the right ramus of the lower jaw of a large Saurian, probably that of Pliosaurus. This sandy bed, as a commencement of the Rhætic series, does not seem to be elsewhere of usual occurrence, the lowest stratum below the bone-bed, in most other localities, being the well-known black shale, of a character more or less indurated, which at Garden Cliff, Wainlode, Coombe Hill, Penarth, and elsewhere, as described by Dr. Wright in vol. xvi. of the Society's Journal, and at Batheaston and Westbury, as de scribed by Mr. Moore in vol. xvii. of the same publication, forms the base. At Beer Crowcomb, however, as described by the latter, we find a pale-blue stone, 1 foot 2 inches thick, with vegetable-like markings, followed by blue shaly marl, given as the lowest bed of the series, which may be taken as the equivalent of the lowest Gainsborough bed; and perhaps at the well-known Aust Cliff locality, where the bone-bed is described by Dr. Wright as lying abruptly on the Keuper, the stratum of pale arenaceous marl, 1 foot in thickness, which, though placed by him on the top of the Keuper, in texture apparently resembles the lowest Rhætic bed of Gainsborough, may be another of its equivalents. This, however, I hazard only as a conjecture, and on the slight supposition that the fossils of the Rhætic type, should it contain any, are so few as to have hitherto escaped observation. Following the line in a southerly or south-easterly course towards Lincoln, which coincides with the direction of the dip, we find in corresponding order the various beds of the series laid bare, the next of which, No. 2 in the section, consists of a stratum of black fissile shale, 8 feet in thickness, containing nests of pyrites, and having several thin, non-continuous Fig. 1.-Section of the Rhætic Beds near Gainsborough. Keuper Marls. ΟΙ Horiz. scale do. 50 Vert. veins of grey pyritous stone imbedded in it. The main bulk of this deposit seems to be entirely wanting in fossil remains; but, after a minute search, it has yielded a few coprolites and specimens of Avicula contorta and Schizodus cloacinus lying close above the lowest bed No. 1, the presence of these bodies being indicated by layers of iron pyrites, with which mineral the entire series is thickly studded. This black shale is succeeded by the coprolite- or bone-bed (No. 3), a narrow band about an inch thick, entirely composed of worn bones, teeth of various kinds, scales and coprolites, imbedded in a hard cement of sulphuret of iron. Amongst the fossils found in this bed are a portion of the jaw of Lepidotus Giebeli, Alb. ?, teeth of Hybodus minor, H. plicatilis, Sargodon tomicus, Saurichthys apicalis, Acrodus minimus, Gyrolepis Alberti, Termatosaurus Alberti, and Ichthyosaurus, with scales of Gyrolepis, spines, and other animal remains, for the naming of which, as well as of most of the other fossils mentioned in this paper, I am indebted to the kindness of Mr. R. Tate, F.G.S. The unbroken condition of the soft coprolite bodies in this deposit points, so far at least as the Gainsborough bed is concerned, to its formation in a moderately deep sea, or, more likely, in a quiet lagoon or semi-inland sea, where the attrition of the waves was not great; and the curious nature of the contents of the bed seems to denote it as simply of fæcal origin: nor is this view irreconcileable with the invariably fragmentary nature of the harder animal portions imbedded in it; for, mixed with the fæces, would naturally be found the teeth, scales, and other insoluble fragments of the animals preyed upon and the idea of its being simply a fæcal deposit is borne out further by the occurrence, here and there in the bed, of small smooth pebbles, principally quartz, which in all probability the fishes of those days, like the cod and other fishes of our own, that take their food off the ground, had swallowed, either by chance or purposely (for the sake of the zoophytes and other substances incrusting them). Resting upon this bone-bed we find a stratum of loose grey micaceons sandstone (No. 4 in the section) about 4 inches thick, which is by far the most productive bed for fossils in the series, literally abounding in bones, teeth, scales, and coprolites, with spines of Hybodus and Nemacanthus, and casts of Modiola minima, Pullastra arenicola, and other well-known Rhætic fossils. Above this richly fossiliferous bed lies another narrow band of animal débris, No. 5 in the same section, about an inch thick, which may be regarded as a second bone-bed, similar to those found in various other localities. The remains in this band are chiefly coprolites; and, unlike those in the bone-bed below, they are not consolidated in a matrix of pyrites, but lie loose and free in a sandy coating of a composition similar to that of the bed last described, though of a slightly darker colour. This second bone-bed is succeeded by another band of black shale (No. 6), 2 feet thick, containing Avicula contorta and other fossils, and that again by a rather hard finegrained micaceous sandstone (No. 7), 6 inches in thickness, the mica in some parts lying in large loose scales. This bed is highly pyritous throughout, and contains a few teeth, scales, and coprolites, with abundance of Avicula contorta on its upper surface. Above this comes another bed of black pyritous shale (No. 8), 2 feet 4 inches thick, containing immense numbers of compressed Avicula contorta, Schizodus cloacinus, and other fossils, and having at wide intervals large, flat-shaped, concretionary nodules, of homogeneous texture throughout, imbedded in its mass. In the more fossiliferous parts this bed is very flaky, and separates easily; and the flakes, which may be split up into the thinnest slices, seem to be composed of nothing but dead organisms, of which the shells of Schizodus cloacinus form the bulk. These last-mentioned shales are capped by a band of very hard, compact, laminated, micaceous sandstone (No. 9), 1 foot 5 inches thick, of a light-grey colour, containing numerous casts of Avicula contorta, Pullastra arenicola, Modiola minima, and Perna, sp., with teeth, bones, coprolites, and drift-wood. This band forms by far the most important of the stone-beds, and has been used largely for the roadways round the new station at Gainsborough. The fossils in it have not uncommonly a bright pyritous covering, rendering them very distinct and clear in the surrounding matrix of grey. The markings on this stone-bed are most singular, many of the slabs presenting apparently traces of the mollusks and annelids that crawled over and burrowed in them, with smooth wave-ridges and hollows, the latter filled with shells and fish-remains, just as may now be seen on any sandy shore which the retreating tide has laid bare. This is followed again by a bed of shale (No. 10), 4 inches thick, similar in composition to the other shaly strata, containing Avicula contorta and Schizodus cloacinus in great numbers, above which comes another narrow band of rather dark sandy stone (No. 11 in the section), 2 inches thick. Then another bed of fissile shale (No. 12), 1 foot 6 inches thick, containing the same fossils as before; above which is another band of stone (No. 13), similar to No. 11, 2 inches thick, and above it shale, as before, 1 foot thick (No. 14). Then comes a remarkable narrow band of highly pyritous stone (No. 15), an inch thick, apparently unfossiliferous; and succeeding it is another bed of shale (No. 16) 1 foot 6 inches thick, similar to all the preceding. Then a band of stone (No. 17), 2 inches thick, much broken, resembling in this respect the beds of rubble found at the top of Oolite cliffs. This band, which, so far as I have observed, is wanting in fossils, is followed by another bed of shale (No. 18), 3 feet thick, containing, like No. 8, immense numbers of compressed Avicula contorta and Schizodus cloacinus, with here and there noncontinuous veins of black fibrous gypsum running horizontally through the mass, and having near its surface large oval-shaped nodules of septaria, differing from those in No. 8 (which are of solid and homogeneous texture throughout) in being partly hollow, and having their interstices filled with small crystals of carbonate of lime. It is worthy of remark that, where these septaria occur, the black shales directly beneath them dip for a certain distance, and are rounded and compressed by their weight, while the stone-bed above bulges out in a dome-shaped mass, apparently showing that the concretionary action to which these bodies owed their growth |