Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/173

Rh at Kessingland for a distance of 1200 paces towards Pakefield, terminating abont 500 paces south of the Lighthouse gorge.

It is composed of an unstratificd tenacious clay of a slate-blue colour, occasionally mottled with brown, and sometimes containing patches of brownish stratified sand. It is shown in places to be underlain by sand and indurated gravel; and its upper surface is throughout penetrated perpendicularly by rootlets. It contains minute particles of chalk, specks of carbonaceous matter, and a few small stones; and from it, and from the underlying gravel, mammalian remains are obtained. At its northern termination, where bed No. 3 rests upon it, freshwater shells, chiefly Unio tumidus, occur at its base, and in the gravel-bed below it. Its upper surface is remarkably even; and it is occasionally overlain by a few inches of sand or indurated gravel. Its greatest thickness seems to be about 8 feet.

No. 3, which is about 6 feet at its greatest thickness, fills a lenticular hollow, cut out of beds Nos. 1 and 2, as shown in the accompanying sections. It is not penetrated by roots, as is No. 2, but contains at its base an accumulation of wood debris. It is finely laminated, and extends about 250 paces from end to end, being shown in places to be underlain by sand and gravel. It varies in colour and composition, resembling at its southern end the black unstratified clay on which it there rests, while northwards its colour changes to a rusty brown. Unfortunately the section is now (March 1876) much obscured by talus, especially at the point where in November 1874 I saw the junction between beds Nos. 1 and 3 so clearly exposed. The view has been consequently advanced that the laminated clay, No. 3, is merely the continuation of the Chillesford Clay, No. 1. To this I reply, that the two beds differ widely from each other in appearance and composition; that the Chillesford Clay being a deposit remarkably sui generis, and easily recognizable, the supposition that the laminated bed is a local modification of it cannot be admitted. In 1874, as I have observed, the section showed most clearly the one bed resting on the other, as shown in fig. 1, which is a copy of the sketch made at the time in my note-book.

Moreover the palæontological agrees with the physical evidence. Wherever the sand and gravel at the base of the Chillesford Clay, or that Clay itself, yields molluscan remains, they are those of marine species, except that in some localities a small admixture of fresh- water forms imparts a slight fluvio-marine aspect to the formation. In the gravel, however, which underlies the laminated bed in question the mollusca are entirely of freshwater species, being principally Unios with both valves united and clustered together nearly as they lived.