Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/495

 Sutton (and possibly the Sudbourne) reef, and scattered over the bed of the Red-Crag sea (fig. 23). The circumstance of the occurrence of large masses of flint, covered with Balani, and of pebbles derived from distant formations indicate transport, probably by ice-action; for the flints are of considerable size and perfectly unrolled. They seem to have been dropped where they are found ; and it is a question whether the Balani with which many of them are covered may not have been attached on the coast before their removal. This removal necessarily requires a certain depth of water, as also would the accumulation and reconstruction by sea-currents of the mass of sand and comminuted shells forming a great portion of the Red Crag. The character of the fauna of the Red Crag is in accordance with these conditions. Littorina littorea, Purpura lapillus, Cardium edule, Pholas crispata, Teredo norvegica, and Mytilus edulis clearly indicate shore-lines ; whilst the several species of Astarte, Trophon, Turritella, Cardita, Nucula, together with the common Pectunculus glycymeris, Pecten opercularis, Mactra ovalis, and others, are confined to the laminarian and deeper zones.

If we suppose a shoal to have been formed in one part of this sea-bed, and subsequently, owing to a change in the currents, to have become subject to a scouring action in another direction, the top of this shoal would be thrown forward in successive laminae, steep in proportion to the velocity of the water, and thus form oblique lamination, such as is so common in the Red Crag. Fresh currents may afterwards have removed other shoals and spread them over these obliquely laminated beds in a series of horizontal layers, which, in their turn, may have been scooped and hollowed out, and the depression filled by a newer accumulation — a case not at all uncommon in the Red-Crag district. This, again, may have been planed down and re-covered obliquely by a fresh removal of adjacent shoals. In this way we may have an infinite number of repetitions of the same materials. This constant shifting and readjustment of materials would, at the same time, lead to the heavier portions, such as the bones, the pebbles, and the phosphatic nodules, being thrown down and left behind when the lighter materials were removed, and would thus tend to accumulate them in the basement beds where we now generally find them.

The consequence of these reconstructions is that a large proportion of the shells are worn or broken, and the mass of them are finely comminuted. The presence of some entire and double shells shows that there were more sheltered places. That there were also intervals of repose and quiet is evident from the circumstance that thin horizontal seams of very finely laminated clays and sand were occasionally formed ; these we find interstratified at places with the beds of shelly crag.

I have mentioned that, at Bawdsey, I found a bed of micaceous sandy clay with laminae covered by ripple-marks, which laminae were continued in regular succession for a thickness of several feet. They were formed probably in shallow water (fig. 7). In some cases beds of clayey sands seem to have been raised above the sea-level,