This idea receives some countenance from the fact of the tertiary strata, at their junction with the chalk and the London and Hampshire basins, often consisting of dense beds of sand and shingle, as the Addington hills, near Croydon. They also contain occasionally fresh-water shells, and the remains of land animals and plants, which indicate the former presence of land at no great distance, some part of which may have occupied the centre of the Weald.' The very facts which Lyell here adduces to prove these beds to be the result of his favourite submarine denudation, I think prove them to be beds of drift, deposited on dry land, from subaerial denudation, that is, the wash of rain.

This subject, under the head of drift and alluvium, will be considered in the fourteenth chapter. But as mistakes are constantly made between drift, alluvium, and tertiary strata, and as it is perhaps impossible strictly to distinguish between them, I will state here the sense to which I shall endeavour to confine myself when I use the words. Drift is coarser alluvium, driven along the surface by strong floods, and deposited on land, or left in valleys, where the finer materials have been washed away, in both cases unstratified. Alluvium is finer drift, partially stratified, deposited on land, from materials

held in suspension by water running or standing for a time. The deposits of alluvial plains are alluvium, though enormous quantities of drift may be mingled with them. Tertiary strata are deposits from water in water; but so are all new alluviums in the sea and in lakes. Nay, in lakes the deposits near the shores partake very much of the character of drift, beyond this of alluvium, and in the centre they are perfectly stratified. Where are we to draw the line in these cases? and especially where are we to draw the line between new alluvium in the sea and tertiary strata? There is, however, a clear line between deposits on land and deposits in water; and to deposits on land I confine the words drift and alluvium. The enormous beds of drift and alluvium deposited on land, contiguous to river-courses, and resulting from the formation of valleys, &c., are constantly quoted as tertiary strata.

I contend, however, that the lips of the pink tertiary strata must have joined over the chalk, making these strata of the London basin and the Hampshire basin continuous over the Wealden ridge (not valley). The Alton hills, which form the west border of the Wealden region, are still capped with the last remains of tertiary strata. And doubtless the so-called Druidical sandstones

and conglomerates of this otherwise chalk district are remnants of these tertiary beds.

In the horse monument at the foot of Brookwood Hill, I brought the largest of the sandstones from the top of the clay-capped chalk ridge north of the road between East and West Meon. The next largest flat one I dug out from two feet below the surface of the drift-gravel on the east side of Bramdean. It may, perhaps, have never moved horizontally, or very slightly, but have been gradually and constantly undermined during the excavation of the valley, and so let vertically down. A large stone so situated may be rounded by the passage of water, sand, and small stones in floods, and by the action of the atmosphere, and so assume the form of a huge boulder without having been itself moved. And where extensive regions of soft strata vanish by denudation, they will leave any accidental rocks or hard parts of their contents behind them in the form of huge boulders.

To illustrate this in a small way: the drift at the bottom of one of our Hampshire deans or valleys may contain a sifted assortment of the contents of the whole mass which once was above the valley, as well as the run of the hills' which now form its sides; so that, of two flints there lying in contact, one may be the untravelled,

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