only be existing now, but greatly widening. Yet there are no more fissures there than in any other system of valleys. It is needless to remark, that a rise of four feet in a century would in no way disarrange the drainage of the country. And it has required all the sagacity of the greatest philosophers to ascertain that this vast operation has taken place, and is still progressing.

6

I must confess that I have not had an opportunity of examining these mathematical methods' of Mr. Hopkins's. But according to my mathematics, if the valleys of the river-courses of the Weald are igneous fissures, they should grow wider as they ascend. They should be widest at the top of the Forest Ridge, and should narrow off to nothing at the sea on the south, and at the Thames on the north, and this irrespective of comparative hardness of ground. The reverse of this is the case. Like any other waterslopes, these valleys start without any fissures at all; that is, the run of the whole surface of the high grounds is first received into an infinity of coombs, which have no permanent streams; and all these coombs, running from every direction, slope into a multiplicity of narrow valleys with rivulets, also running

in

every direction. And, like any other waterslope or system of valleys, instead of narrowing,

they widen as they descend, except where the

The sea is eroding the coast of Sussex.

ground is harder than the ground above it, that is, up stream of it. The reason for this will be given immediately.

Lyell says: It is evident that these openings, so far at least as they are due to aqueous erosion, have not been produced by the rivers, many of which, like the Ouse, near Lewes, have filled up arms of the sea, instead of deepening the hollows which they traverse.'

As these rivers have filled up arms of the sea, I have given a reason why they never can deepen their channels at the mouths as long as the sea and land keep their present relative level. More than this instead of deepening their channels, they will build their banks and beds up higher than they are, as the rivers in alluvial parts of valleys always must at every overflow. But this subject will be considered in the last chapter.

According to Lyell the sea is at present eroding the coast of Sussex. The following is from the 'Principles.' 'About a mile to the west of the town of Newhaven the remains of an ancient entrenchment are seen on the brow of Castle Hill. This earthwork, supposed to be Roman, was evidently once of considerable extent, and of an oval form, but the greater part has been cut away by the sea. The cliffs, which are undermined here, are high; more than 100 feet of chalk being

covered by tertiary clay and sand from 60 to 70 feet in thickness. In a few centuries the last vestiges of the plastic clay formation on the southern borders of the chalk of the South Downs on this coast will be annihilated, and future geologists will learn, from historical documents, the ancient geographical boundaries of this group of strata in that direction. On the opposite side of the estuary of the Ouse on the east of Newhaven harbour, a bed of shingle, composed of chalk flints, derived from the waste of the adjoining cliffs, had accumulated at Seaford for several centuries. In the great storm of November 1824, this bank was entirely swept away, and the town of Seaford inundated. Another great beach of shingle is now forming from fresh materials.

6

The whole coast of Sussex has been incessantly encroached upon by the sea from time immemorial; and although sudden inundations only, which overwhelmed fertile or inhabited tracts, are noticed in history, the records attest an extraordinary amount of loss. During a period of no more than eighty years there are notices of about twenty inroads, in which tracts of land of from twenty to four hundred acres in extent were overwhelmed at once.'

With this devastation going on in these days, one would suppose that if in former days the sea

Yet the rivers

are filling

their estuaries.

made the valleys of the Ouse and the many other rivers in its neighbourhood, if it did not continue to erode and enlarge these valleys, it would at least keep them open.

But the sea erodes the outside of the land, not the inside of it. Instead of eroding the inside, the sea, which is devouring the outside of the land, has allowed the rivers to dam it out of the inside of it, to fill up arms of the sea. And with what materials have the rivers filled these arms of the sea, since they have not produced the openings,' and are not deepening the hollows which they traverse ?' But parvis componere magna: let us ask this question on a larger scale. If the sea made the valleys of the Rhone, Po, Mississippi, Ganges, and Niger, why does it yield to these rivers now, and allow them to protrude deltas of thousands and thousands of square miles? One answer replies to both questions.

Though the Ouse must cease to deepen its channel where it is level with the sea, at this present time there is not a heavy rain falls on the upper valley of the Ouse, but it deepens, lengthens, and widens that valley. And this is the case, not only with that valley and the valleys which I have enumerated, but with every valley in the wide wide world. And hence the materials which fill arms of the sea, and form alluvial plains and

deltas, unless the land is rising, or alongshore currents and tides interfere by sea, or lakes catch the alluvium by land. The gradient of a valley is never permanent in any part. Every valley is always lengthening at the upper end or decreasing in height there; and all intermediate parts are perpetually in process of being planed down, or built up to one uniform gradient from the head of the valley to its mouth, or to the end of the delta, if there be one.

Valleys are always increasing, hills always decreasing. Indeed, valleys exist only in the dissolution of hills. But sedimentary strata are not formed only from the contents of valleys. The entire surface of the solid part of the globe, the earth, is always being washed by rain into the liquid part of the globe, the sea.

A

We are not to imagine that it is in the Weald only that rivers run through ridges of hills. glance at a physical map of England or the

World, will show plenty of examples. Hopkins going to account for these fractures' by 'mathematical methods?'

6

Is Mr.

cross

A stream running through ridges, large or small, is the simple consequence of the differing hardness of the ground through which it runs. In all cases a stream cuts for itself a narrow channel, the depth of which is determined by