CHAPTER XX.

CHANGING COURSE OF STREAMS—­DEWPONDS—­A WET HARVEST—­WEATHER PHENOMENA—­WILL-O’-THE-WISP—­VARIOUS.

“There rolls the deep where grew the tree. 
O Earth, what changes hast thou seen!”
—­In Memoriam.

“With many a curve my banks I fret
By many a field and fallow,
And many a fairy foreland set
With willow-weed and mallow.

“I chatter, chatter, as I flow
To join the brimming river,
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 surface thus created by the river or brook’s course perpetually deflected and reflected, is finally completed by the floods bringing down a deposit of soil in solution, which is precipitated and settles into any surface irregularities left by the wanderings of the stream.  A faint conception of an absolutely illimitable cycle of years, during which the whole extent of visible flat meadow has been again and again eroded and restored, is thus conveyed.