For men may come and men may go,
But I go on for ever."
_The Brook_.

Living so many years in one place I had unusual opportunities, as my
rounds nearly always took me beside my brooks, of watching their
slowly changing courses. The roots of the pollard willows helped to
keep them to their regular path by holding up the banks, but sometimes
when an old tree fell into the water it had an opposite result. A
fallen tree, reaching partly across the stream, has the immediate
effect of damming the flow of the water on the side of its growth and
diverting the current towards the opposite bank in a narrowed but more
powerful advance, so that the bank is worn away and the beginning of a
bend is formed. As the breach increases, the water, momentarily
retarded there by the new concavity, rushes forward again in the
direction of the bank from which the tree fell. So that a second
concavity is produced on that side some little way below the tree,
resulting in the slow formation of an extended S-like figure, or hook
with a double bend. The collection of rubbish and sediment retained by
the fallen tree helps to form a new bank on that side, extending
further into the stream than the bank on which the tree originally
stood.

As this process continues it is easy to see that a straight stretch of
stream will in time assume a winding course, and the stream will be
continually altering its path, so that large areas of flat meadows
will be formed, every part of which has at times been the stream's
course. How many ages, then, must it have taken to produce the level
meadows we see extending for immense distances on either side of our
big rivers, and even those adjoining quite small streams? The level