The evidence of so unexpected a fact as the infra-position of a dense mass of purely freshwater origin to a deep-sea deposit (a phenomenon with which we have since become familiar, in other chapters of the earth's autobiography), was received, at first, with no small doubt and incredulity. But the relative position of the beds is unequivocal; the Weald Clay being distinctly seen to pass beneath the Greensand in various parts of Surrey, Kent, and Sussex; and if we proceed from Sussex westward to the Vale of Wardour, we there again observe the same formation, or, at least, the lower division of it, the Purbeck, occupying the same relative position, and resting on the Oolite (see fig. 228.). Or if we pass from the base of the South Downs in Sussex, and cross to the Isle of Wight, we there again meet with the Wealden series reappearing beneath the Greensand, and cannot doubt that the beds are prolonged subterraneously, as indicated by the dotted lines in fig. 229. [Illustration: Fig. 228. Cross section. O, Oolite. G S, Greensand, or Lower Cretaceous.] [Illustration: Fig. 229. Cross section.] The minor groups into which the Wealden has been commonly divided in England are, as before stated, three, and they succeed each other in the following descending order[227-A]:-- Thickness. 1st. Weald Clay, sometimes including thin beds of sand and shelly limestone 140 to 280 ft. 2d. Hastings Sand, in which occur some clays and calcareous grits 400 to 500 ft. 3d. Purbeck Beds, consisting of various kinds of limestones and marls 150 to 200 ft. _Weald Clay._