4 THE UNDERGROUND WATERS OF NORTH-WEST YORKSHIRE. 
the Silurian, but there is one at Spiggott Hill at the South 
West corner of the Tarn out of the Silurian, and another in 
the lower Streets. Malham Tarn rests on the upturned and 
denuded edges of the Silurian rocks, and is dammed in as to 
its sides with drift, and deepened by an artificial embankment 
at its outlet. The lake discharges at its south-east corner, and 
the outflow soon crosses the North Craven Fault on its line from 
the Smelt Mill eastwards, and sinks in the limestone at the 
well-known sinks. 
Further east under the escarpments about Middle House, 
the east side of Great Close, and on High Stoney Bank, rise 
several streams which together form Gordale Beck. These are 
on the limestone, but, owing perhaps mainly to drift, they keep 
to the surface. They flow over the narrow strip of Silurian 
near where it is dying out ; and, now in one stream, they cross 
the North Craven Fault and proceed down Gordale. By the 
present investigation we now learn that the stream always under- 
goes considerable absorption into the limestone in mid-Gordale, 
and during the summer of 1899 was entirely absorbed. 
There are thus three principal sinks, viz. : At the Smelt 
Mill, Malham Tarn Sinks, and in Gordale ; while curiously 
enough there are three principal outlets, viz. : At Malham Cove, 
Aire Head, and in Gordale bottom on the east of the main stream 
between the falls and Gordale House. 
To trace each sink to its outlet, and conversely each outlet 
to its source, is the problem. 
How long it is since the w^aters of Malham Tarn ceased to 
flow regularly down Comb Scar, and over the top of Malham 
Cove, but took instead to disappearing in the limestone at the 
several " sinks," is not known. 
The earliest information available is of a time when the 
Cove itself was only over-run by the stream on rare occasions 
during exceptional floods. More frequently the water overflowed 
Comb Scar, but sank at its foot ; whereas now it fails even in 
a flood to get as far down the valley as Comb Scar. 
