^{page 99 note 2} It has been contended that the Thames was once a tributary of the Rhine, but this argument can only have been supported by those who have not studied the structure of the valley, and of the East of England, with the minuteness that would show such I a view to be at variance equally with the mode in which the valley was first formed, and with the conditions which it subsequently underwent, i.e., with its excavation through the Drift by denudation on emergence from the Upper Drift sea, and its subsequent history as given here in outline.

^{page 100 note 1} As the Ordnance Sheet, No. 1, which comprises the entire valley of the Thames, from London to the sea, has not yet been mapped by the Geological Survey, I subjoin the eastern and northern boundary of the Thames gravel through it: all the names of places being those on the Ordnance sheet. Starting from a point about midway between Cheshunt and Broxbourne, the eastern boundary of the Thames gravel follows the course of the Lea on its eastern side very closely, and at a distance varying from a furlong to one mile from that stream itself as far as Walthamstow, at which place it turns abruptly to the east, and passing through Forestside, bends for two miles up the Roding valley, for a mile above Woodford Bridge, whence it descends due south for an equal distance; then, turning round Clay Hall, it stretches E.N.E. to Fairlop plain. Then sweeping S.E., the boundary curves round Lawn Farm at a distance of six furlongs on the west and south sides of it, and bending E.N.E. again to (the northernmost) Collier Row, it curves from that place southwards passing through “Priests,” eastwards, but with a slight northerly curve, to Hare Hall. It crosses the railway at Hare Lodge to New Readingcourt; then, turning abruptly, it runs S. by E, to Upminster Bridge, whence it stretches E.S.E. to (Orsett) Fengate, passing in its course, and immediately south of them, the villages of Upminster, Cranham, and North Ockendon. It then bends close round the north side of Orsett to Rotten Row, whence it turns north to Horndon-on-the-Hill, which it touches on the south side, then trending east, it crosses the Yange Road half a mile N.E. of Stanford-le-Hope; then bending N.E. for a mile it curves again, and crossing the road from Corringham to Laindon, six furlongs W.N.W. of Corringham, passes to Fobbing, crossing that village one furlong north of the church, when it abruptly bends south, and keeping close to the village, passes in a S. by E. line to the Marsh, a furlong east of Fobbing Wharf, where it stops; but as it appears at the bottom of the dock there, it is probably continued under Corringham Marsh to the river, a mile west of Thames Haven. This boundary, which I have tested minutely, will, after quitting the Lea, be found to be almost identical with the line of the Thames River, except in those reaches which have ueen formed subsequently to the gravel by the faults described in the text, viz., Sea Reach, Gravesend Reach, Erith Rands, and Woolwich Reach, with the lines of which, however, it shows not the remotest coincidence. The Geological Survey Sheets, Nos. 7 and 8, purport to show part of the formation west of London; the gravel of Wimbledon and Richmond Hills, however, is not included as any part of it; but sheet No. 13, which should contain the westerly extremity, including the great expansion of the formation around Reading, has been published without any delineation of the grtater portion of the formation comprised in it.

^{page 103 note 1} Although when the gravel at Beddington or Carshalton is compared with that near the Thames the contrast is considerable, yet from the flatness of the intervening country it is impossible to say where one begins and the other ends; indeed, if the partial continuity with the sea remained, the two must have blended. The railway cutting at Peasemarsh, near Tooting, shows the same coarse gravel as the Mitcham cuttings; but it is too shallow to disclose whether this rests on any different gravel.

^{page 104 note 1} If the places of the Plumstead fault in Section 3, and of the Cliffe fault in Section 5, be marked on the map, and a ruler laid through them, it will indicate the direction of a rectilinear line of throw extending from the Cliffe fault, and passing exactly through the faults of Little Thurrock, Purfleet, Erith, Plumstead, and Lower Charlton.

^{page 104 note 2} The extensively-spread gravel of the Middle Drift, which partially underlies the Boulder-clay, lies without the brow of the Thames Valley, except for a small distance in the western part of it.

^{page 105 note 1} I confine the term Drift to the English Glacial beds that are older than the valleys existing in strata which are newer than the Trias, and lie south of Flamborough Head; using the term Post-glacial for such as are newer

^{page 105 note 2} That the climatic conditions producing gravel were not changed, is shown by the formation of the later gravels (x 5); and I have seen in the Upper Brickearth at Wanstead large angular chalk flints, apparently ice-borne.

^{page 106 note 1} It would incumber the paper to show why, since the original valley was cut through the drift, no outlier of drift should occur on the top of Shooters' Hill, corresponding to that on Havering Hill; but it is capable of a very clear and interesting explanation. To give it, however, would require a description of the position which the Upper and Middle-drift occupies in Essex, Middlesex, and elsewhere.

^{page 106 note 2} To make this view intelligible, it is perhaps necessary to explain that I regard the gravel of Southend (which, separated from the Thames gravel hy several miles of gravel-less country, extends in the form of a narrow strip behind the marshes bordering the North Sea for nearly 20 miles in a NN.E. direction along the coast of Essex, and is capped in places by Upper Brickearth, and which, although it is the same as that fringing the estuary of the Medway between Rochester and the Nore, I will distinguish as the “East Essex gravel”) as a remnant of a great sheet of gravel that was deposited in an estuary whose mouth joined (near Rochester) the sea, then extending over the Wealden area prior to the excavation of the Weald Valley. This estuary, starting from the point where its mouth, inosculated with that of the Thames gravel channel, south-west of Rochester, extended in a NN.E. direction through what is now the mouth of the Medway, and traversed a land-tract, of which the greater part occupied the area now represented by the mouth of the Thames, and by that part of the North Sea which is known as the Swin, such tract having been submerged by the convulsions giving rise to Sea Reach. The mouth of this estuary discharged into the sea over the Weald, in contiguity to the south-eastern mouth of the channel of the Thames gravel, the subsequent elevation of the Weald and submergence of the North Sea having reversed the direction of the drainage through the valley of the Medway, so that it now flows northwards into the North Sea, instead of southwards, as it did during the Thames gravel period, and for several stages subsequent to that period, into the Weald. To show the grounds for this view, however, it would be necessary to describe the condition of the valleys of the Aide, Deben, Orwell, and Stour, and especially the condition and structure of the valleys of the Blackwater and Crouch. It must be obvious, however, that if the Thames gravel were the deposit of the present valley at a time when the country generally stood at a lower level (whether accompanied by floods or not), then, not only should that gravel extend to the Thames mouth, but these six valleys, which open, like that of the River Thames, into the North Sea, and are all, in some part of them, cut either through the Boulder-clay, or else the Middle Drift, should, like the Thames valley, contain a sheet of gravel similar to x 4″; whereas, although the four first-named valleys contain occasional patches of gravel analogous in position to that described as x 2, nothing in any way corresponding to the Thames gravel (x 4″) exists in them, while, in the case of the gravel-less valleys of the Crouch and Blackwater, it can be distinctly shown that both of these valleys, for two or three miles of their course (but in the case of the Blackwater on its iouth side only), cut like the Thames mouth at right angles through the “ East Essex gravel.” The terracing down of this East Essex gravel into the valley of the Weald; first to beds analagous to x 5 and x 5', then to the gravels of the Lower Green Sand terrace, around Maidstone, and, lastly, to the gravels of the Weald Clay bottom, prior to the reversal ensuing on the formation of Sea Reach, may be distinctly shewn; as the terracing of the Thames gravel, may, in like manner, be traced through the Darent and Cray Valley beds, to the gravels of the Lower Green Sand terrace near Sevenoaks.