Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/182

88 tificial excavation, if other sections, such as fig. 19, did not exist close by. The gravel (c) fills up the inequalities in the sand.

Fig. 20.—Section in Erith Pit.

Rearranged Thanet sand is frequently met with in these gravels, which were formed out of materials derived from this bed during the excavation or deepening of the Thames valley and its tributaries at this period. The large bull's-head flints from the basement-bed are carried down to lower levels (owing to their weight) and deposited on the new surface of the chalk.

The pebbles from the Woolwich bed are most abundant in the middle part of the Thames Quaternary series, and have been carried a great distance from and below the escarpment before they were redeposited in the gravel.

Fig. 21 is from a drawing on wood by Mr. S. Skertchly of a mass

Fig. 21.—Erith Pit.

of Thanet sands (b) 38 feet in length by 7 feet 10 inches in width, with a portion of the Woolwich pebble-bed attached to it, lying upon and against one piece of the Woolwich shell-bed 12 feet by 6 feet