Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/280

186 gracilis, Terebratula semiglobosa, and Plicatula inflata. The band b, in thickness about 1 foot 2 inches, is conspicuous for a meandering and many-branched sponge, Siphonia paradoxica, specimens of which are visible in the cliff only in short lengths, but on the fallen blocks washed by the sea are seen to extend continuously and horizontally over many square feet of surface. The underside of b departs from the general arrangement in the other courses; for its base, instead of forming a flat or approximately flat floor, is broken up into a series of irregularly rounded ridges and hollows, which undulate perpendicularly within the limits of a few inches, and are represented in the section. The fossils from this bed, b, are not so many (numerically speaking) as those in a; the chief forms are Siphonia paradoxica, Terebratula biplicata, Terebratula semiglobosa, var. undata, Kingena lima, Avicula gryphoeoides, and Inoceramus latus.

Next in succession, in descending order, is the red stratum, locally called the "Red Chalk," marked by an abundance of organic remains, some of which, as Bourgueticrinus rugosus and Terebratula capillata, are, in England, special to this deposit. Lithologically, it is unlike the beds above it from the fact of its abounding in great numbers of rolled and subangular pebbles of quartz, slate, &c., which for the most part are of small size and insignificant, though occasionally assuming larger dimensions. In appearance it is divisible into three almost equal portions, of which the first (A) has towards its base a large quantity of fragments of Inocerami, the second and thickest division (B) is rich in Belemnites, and the third and lowest (C) yields many Terebratuloe. The bands A and B are exceedingly hard and stony, and sufficiently tabular in character to have offered a plane of resistance to former upheaving forces, and to have afforded great support to the overlying white beds; thus, although the whole cliff was evidently, in ancient geological times, much disturbed, the perpendicular fissures, which rise out of the yellow bands (X, Y), cease just before reaching the layer B, affect the red beds to the right and left of the points of application, and then start upwards through the white stratum in new positions and in greater number. The colouring-matter in A is less equally distributed than in B and C, and seems to have been accumulated as an envelope around irregular spheroidal masses; in B the tint is of a lighter, and in C of a darker shade than in the highest division. The middle bed (B) is in substance the hardest and most homogeneous of the three; the last (C) is the least compact. Viewed in the cliff, A wears a mottled aspect, B a nodular facies, and C a plane surface. Towards the base of the bottom bed (C) the hard limestone character of the Bed Chalk is lost, and the stratum degenerates into a somewhat sandy incoherent mass, hardly differing from the underlying yellow division except in colour. On account of the less compact nature of the last of the three red beds, fossils are more easily procured from it, have their surfaces in better condition, and are more readily seen when of small size. Resting on the top of A and filling the undulations on the underside of the lowest white bed (b), is a bright red argillaceous substance, very friable.