158 AUTUMN AND WINTER 



reservoirs ; but it is weeks or months before they saturate 

 the thirsty depths of the soil, and produce a visible result 

 in the swelling of the springs. Deep wells and streams fed 

 by springs are often lower in November, or even December, 

 than in August, in spite of six or eight weeks' plentiful rain. 

 The surface water soon runs away when the weather clears ; 

 and though the young wheat springs wholesomely from the 

 moistened soil, the shrunken brooks retain a curious aspect of 

 bygone summer. Minnows still play on the shallow fords, 

 as in the July heats ; and the water- wagtails on autumn 

 passage run daintily on the half-covered gravel. 



The autumn rains do not seem to fulfil their promise until 

 the springs and wells begin to rise about midwinter. The 

 most striking example of the delayed effect of the autumn 

 rains is the flowing of the periodic streams, which are 

 common in chalk and mountain limestone districts, and are 

 known as winterbournes or nailbournes. The meaning of 

 the latter name seems to be unknown, though that of the 

 former is clear. The flowing of the winterbournes can often 

 be foretold almost to a day by old inhabitants, or by water 

 engineers ; they usually begin some time in January or 

 February, and run at an even height until early summer. 

 The regularity of their appearance and flow is due to the 

 homogeneous structure of the mass of chalk or limestone out 

 of which they burst. The surface water sinks evenly through 

 vast layers of the porous rock until the level of the accumu- 

 lated supply rises above one of the vents in an upper valley. 

 Then it starts flowing, and the spring draws an equal 

 volume from the great internal sponge, until the water- 

 level once more falls beneath it. After a long series of dry 

 years, these streams are often quiescent for several seasons. 

 The winter following the extremely wet summer of 1903 

 was the first in which many winterbournes had run for a long 



