The valley at its upper end
spreads out like the fingers of a hand, as the gullies in tide-muds
do.
But that hypothesis will not stand. There is no vast unbroken flat
behind the glen. Right and left of it are other similar glens,
parted from it by long narrow ridges: these also must be explained
on the same hypothesis; but they cannot. For there could not have
been surface-drainage to make them all, or a tenth of them. There
are no other possible hypotheses; and so he must fall back on the
original theory--the rain, the springs, the brook; they have done it
all, even as they are doing it this day.
But is not that still a hasty assumption? May not their denuding
power have been far greater in old times than now?
Why should it? Because there was more rain then than now? That he
must put out of court; there is no evidence of it whatsoever.
Because the land was more friable originally? Well, there is a
great deal to be said for that. The experience of every countryman
tells him that bare or fallow land is more easily washed away than
land under vegetation. And no doubt, when these gravels and sands
rose from the sea, they were barren for hundreds of years. He has
some measure of the time required, because he can tell roughly how
long it takes for sands and shingles left by the sea to become
covered with vegetation.
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