Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/468

 oblique lamination, without permanent or definite order of succession in the beds, and the upper by more persistent horizontal bedding. Shells abound in the lower, and are rarer in the upper division.

The general features of the Red Crag are too well known to require more than brief mention. In the central area there occurs at the base of the lower division a bed of phosphatic nodules (the so-called " coprolites "), varying in thickness from a few inches to one or two feet. This bed is slightly developed between Manningtree and Harwich. At Dovercourt I have found remains of it with its characteristic fossils on the top of the cliff ; but it is in the district between the rivers Orwell, Deben, and Aide that it is most largely developed, and most profitably worked *. This bed often has an underlie of large blocks of London-clay Septaria, and of large, entire, and fresh-looking flints derived from the Chalk. In this shingle are also found a considerable number of the larger shells entire, particularly an abundance of Cardium edule, Pectunculus glycymeris, Cyprina islandica, Trophon antiquum, &c, whilst the Septaria are drilled by boring mollusks, and both Septaria and flints are covered with Balani. Large pebbles of siliceous sandstone, balls of concretionary dark fossiliferous sandstone, rolled and worn bones or teeth of Cetacea, Sharks, &c, and occasionally fragments of the older rocks, are also met with in this bed. At a pit at Trimley, near Felixstow, I found subangular fragments of Lower Greensand chert, a large fragment of red granite, and fragments and pebbles of siliceous sandstones. Although this shingle and accompanying fragments of the older rocks are generally confined to the base of the lied Crag, large blocks of angular flint and seams of phosphatic nodules occasionally occur in the overlying beds. Quartz pebbles are met with in the Red Crag, but they are rare.

This basement bed sometimes thins out†, and at other times divides into two beds separated by a foot or two of shelly crag. Sometimes also thin seams of phosphatic nodules occur 3 or 4 feet above the lower bed, and separated from it by a bed of comminuted shells, as at Foxhall, Waldringfield, and, in places, at Sutton. Dispersed nodules may, in fact, be found through the whole of the Red Crag.

Above this basement bed are a series of beds more or less fossiliferous, forming with it the lower division of the Red Crag, which is generally from 10 to 15 feet thick, and rarely attains a thickness of from 20 to 25 feet. These beds are very irregular, not persistent for long distances, often mere lenticular masses, and are marked by the more or less constant occurrence of oblique lamination. This lamination has not a constant direction. It varies to almost all points of the compass. The dip is generally from 12° to 32°. A common dip is about 22°, N.W., and N.E. It is in the upper part of the lower division that false bedding is most general.


 * Particularly in the district which surrounds the central mass of the Coralline Crag of Sutton.

† In the cliff at Bawdsey this basement bed is altogether or almost wanting, whereas half a mile inland it attains a thickness of from 2 to 3 feet.