Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/284

190 Folkestone, in the limits between 30 feet and 70 feet above the top of the Lower Greensand, and still at some distance beneath the Upper Greensand, can be found all the Ammonites and Nautili given in the previous list, together with the Belemnites and the whole of the other species mentioned as peculiar to the Red Chalk, excepting only the Amorphozoa, the Corals, Bourgueticrinus rugosus, Torynocrynus canon, Pseudodiadema Brongniarti, P. ornatum, Salenia Wiltshirei, Holaster suborbicularis, Serpula cristata, S. rustica, Terebratula capillata, Rhynchonella sulcata, and Spondylus striatus. The presence of the varietal form of Inoceramus sulcatus (which I have ventured to name subsulcatus) and the extreme rarity or total absence of Inoceramus concentricus are marked features in the upper part of the Gault at Folkestone, define a particular zone, and correspond with what is observed at Hunstanton. That a few species may not be common to both localities is to be expected, seeing that the two places are 150 miles apart, and that the strata must have been deposited at those spots under somewhat different conditions, and in a manner which might not be equally favourable to certain forms of life.

According to the statements of persons resident in the district adjoining Hunstanton, and who have seen inland sections opened for agricultural purposes, the blue Gault with its characteristic Belemnites rests on the Cars tone at Flitcham, 10 miles south of Hunstanton, but rather nearer the latter place, and still close to Flitcham, a red clay occurs immediately under the white chalk, thus connecting the Blue Gault with the "Red Chalk." From Sandringham, 8 miles south of Hunstanton, the outcrop of the Red Chalk can be traced without difficulty and continuously to its last appearance on the surface of the ground near the Lighthouse.

The lithological difference between the Red Chalk with its stony hardness and accompanying minute pebbles, and the Blue Gault with its soft clay, is no argument against the two being geologically equivalent; for as great a dissimilarity exists in the Carstone. At Hunstanton the Carstone stratum is dark yellow and very full of pebbles; at Sandringham, at the corresponding portion, it is a pure white sand. But the evidence which organic remains and local position supply in favour of the Red Chalk being a northern equivalent of the Gault of Kent is singularly strengthened by testimony of quite another kind. Chemical analysis shows that the strong contrast in colour which exists in the case of the Red Chalk and the Gault, and which apparently places them apart, is a combining link between them, the upper part of the Kentish Gault being as ferruginous (only under another aspect) as the Red Chalk itself. This fact, for which I am indebted to Mr. David Forbes, is described in the following extract from a letter written by that gentleman to myself, referring to a comparative chemical analysis of the Gault and Red Chalk, the part of the Gault selected for the experiment having been taken from the Folkestone beds, about 50 or 60 feet above the top of the Lower Greensand, where, for some vertical distance, the deposit is very homogeneous.