THE UNDERGROUXD WATERS OF NORTH-WEST YORKSHIRE. 43 
35 minutes from the opening of the sluices, and in little more 
than an hour the overflow was 150 yards long. On this occasion 
the Cove stream rose 2 inclies. The next day the sluices (both 
be it observed) were opened and the Cove stream rose 2| inches. 
A very large volume of water in this case was employed, and, 
the season being normal, an overflow into the Cove drainage 
resulted. In June, 1899, also a season of normal rainfall, a flush 
was produced by opening one sluice ; a photographic record shows 
that no water flowed beyond the Water Sinks. On this occasion 
not the slightest effect was produced upon the flow from Malham 
Cove ; it is, however, worthy of note that a minute trace of the 
Ammonium Sulphate introduced into the Water Sinks in this 
experiment subsequently appeared at Malham Cove. This appears 
to indicate that the watershed of the saturation was actually 
to a small extent surmounted, but that the increased head was 
so small as to be practically nullified by friction. It may here 
be remarked that the 1899 experiments show decisively that 
a flush affects the springs at Aire Head or elsewhere not by 
the direct discharge of the water admitted to the sinks, but by 
increasing the water pressure in the rock and causing a forward 
thrust which drove other water before it, just as the water 
flowing from a reservoir thrusts water out of our domestic taps. 
The two flushes in August, 1899, both affected Malham Cove. 
They appear to have been of less volume than those recorded by 
Mr. Tate, yet they produced a very marked rise of the stream at 
Malham Bridge. 
The great effect upon the stream issuing from Malham Cove 
may be due in part to a greater volume of water having been 
sent down, but it appears quite certain that during the long, 
unexampled drought which prevailed during July and August, 
1899, the saturation levels in the limestone must have fallen to 
a very marked extent, producing a flattening and lowering of 
the subterranean watershed, which would greatly facilitate the 
overflow from one drainage system to the other. 
Two subsidiary points need notice. It has been suggested, 
as stated in the Introduction, that the tardy response of Malham 
