Now as to Grays: That very pleasant place does give some approach both in soil and contour to the water from the north. It is just on the edge of the chalk, just above the old limit of high water, and its original nucleus, though not actually on the stream, would require but a short causeway to reach it. But Grays is in the same bad topographical case as Purfleet, only rather worse. It is still less of a terminal for any road from the north. It connects with the east only through Stanford and the Horndon roads. To the north of it lay, completely cutting it off from any communication, the belt of marsh of which Mordyke is now the drainage line, and of which Orsett Fenn is the principal survival. We have, then, on the north, only Purfleet and Grays; and both must be rejected. On the south, however, there is a series of isolated natural wharves which approach the main tidal stream, and not only stand fairly steep-on to its rise and fall, but are further of a soil upon their surface which permitted travel and an easy approach to the river in early times. These are, counting from the sea-reaches upward: Gravesend, where the chalk comes right down to the Thames; Greenhithe, where a tongue of the chalk juts out and touches the water; Erith, the point where the gravels, which some mighty stream laid down when the rivers of Northern Europe were discharging ten, twenty, or a hundred times the flood they have to-day, first approach the existing stream. At Woolwich sand and gravel closely approach the river and line it for so considerable a distance as to afford the platform for a fairly large town. Next up-river the same formation of gravels gives at Greenwich a hard along the stream, and immediately above another spit of the same actually touches the river at the point where used to stand the isolated village of Deptford. [Illustration: GREENWICH] Now any one of these natural hards along the south bank of the Thames between London and the sea would have afforded an excellent platform for the crossing of the river. It is true that the Thames is somewhat wider in its lower reaches than at the pool, but the difference was not so considerable as to balk those who first instituted the ferry and later the bridge of London. If one could cross the half-mile of water which lay before one at extreme high tides under the earliest conditions at Southwark, or bridge (as was done so long ago) the four hundred yards of the mainstream, there would have been no difficulty in dealing with the quarter of a mile at Deptford or at Greenhithe, nor even with the rather broader stream opposite Woolwich.