150 Trof. T. Rupert Jones — Intermittent Streams. 



on the relative percolation of water throngh different soils and 

 rocks, including chalk, that all streams are dependent upon the 

 rainfall. The water sinks more or less perfectly and rapidly into 

 the Chalk hills, until it is stopped by an impervious layer of clay, or 

 other dense material, such as the Chalk-marl, or, if this be fissured, 

 the Gault below it. The Chalk is some few hundreds of feet thick, 

 and becomes highly saturated (in its minute cracks and larger rifts 

 and fissures) with the rain-water; and this reaches upwards to 

 a plane coinciding roughly with some of the hill contours, and 

 also sloping down to the levels at which this underground water 

 is discharged in the valleys intersecting the country. These, when 

 cut down as low as, or below, the line or plane of saturation, 

 may be said to " tap " the subterranean store of water ; and they 

 have continuous streams, from weak places in the Chalk, as long as 

 the rain-water saturates the Chalk up to the level of the old springs, 

 which rarely fail. After a larger supply of water than usual 

 (perhaps months after a rainy season, or perhaps soon after a heavy 

 rain, according to the amount of rain and the rate of percolation), 

 the subterranean store of water will rise above the previous average 

 level ; and, reaching some crack or opening in the surface of the 

 Chalk, it will leak out, or run freely as a spring and stream, until 

 the underground water of the hills is reduced to its ordinary level. 

 Snch occasional and temporary outpourings are known as Bourns, 

 Wintei'bourns, Nailbourns, Woe-waters, etc. 



With respect to the empty condition of the Lambourn and 

 Winterbourn in Berkshire, evidently the " plane of saturation " in 

 the neighbouring hills has been reduced to a very low level, below 

 the feeding cracks of the usual springs. If the country has been 

 fortunate in getting plenty of rain of late, it will have full streams 

 again in due time. Mr. Horton says that the plane of saturation is 

 now reduced below the average level of the water in the wells in 

 the neighbourhood of East Ilsley, and that the scarcity of water has 

 been unprecedented for many years. 



Formerly it was supposed that the water accumulated in one or 

 more large reservoirs or cavities, connected by curved fissures with 

 the surface ; and that, when the water had filled both the cavities 

 and the fissures up to and above the highest level of an upward 

 curved pipe-like communication with the outside, the water would 

 begin its outflow, and continue until the lowest practical level was 

 arrived at by this syphon action. This hypothetical explanation of 

 the phenomenon of a winterbourn is now superseded, and thought 

 to be quite unnecessary in view of the facts above mentioned, as to 

 the plane of saturation, and its intersection by valleys, with fissures 

 tapping it at ordinary levels, and its occasional uprise to higher 

 cracks, which give vent to the surplus water at uncertain periods, 

 either shortly or long after heavy rains, as the case may be. — 

 "Newbury Weekly News," January and February, 1885. 



