6 THE UNDERGROUND WATERS OF NORTH-WEST YORKSHIRE. 
reaching the Cove by sinking at the foot of this pass through 
the shattered and fissured stratum with singular noise and 
rapidity." 
From these records it is evident that as the joints in the 
limestone at the "sinks" were slowly widened by the solvent 
action of the water they gradually absorbed the stream, until it 
was only in floods that the w^ater reached the Cove. As the 
process continued the stream dwindled, and retreated from stage 
to stage. From what Mr. Howson says of the flood-water sink- 
ing at the foot of Comb Scar there w^as probably a pause in the 
retreat there of some duration. Now, however, flood-water no 
longer reaches Comb Scar, and the old track is what mid-Gordale 
(where exactly the same process of stream absorption is now 
going on) will one day become — a dry valley. 
With respect to the underground streams it will be seen 
that Hurtley considered the Cove outflow was supplied from the 
Tarn, while Dr. Whitaker ascribes it to the " Smelt Mill " sinks. 
The Aire Head Springs it appears were known by the villagers 
to be connected with the Tarn even then, and one wonders 
whether they had arrived at that conclusion by experiment or 
mere guesswork. It was more or less natural to assume the 
Cove to be the outlet for both the old surface stream from the 
Tarn and the Streets water. Where else could they come? But 
the same process of reasoning would not apply to the Aire Head 
Springs. Anyhow they appear to have known at the close of 
last century all that was known until eighty years later in 1879. 
Mr. Morrison says there is a tradition, but not a clear 
tradition, that Lord Ribblesdale put chaff in at Malham Tarn 
Water Sinks and that it came out at Aire Head. 
Farmers and others have made attempts from time to time 
for many years back to ascertain what the facts really were by 
inserting chaff and similar materials at the sinks, but without 
result. The media employed were never seen again at any of 
the presumed outlets, and so an air of mystery surrounded the 
question and has helped to keep the interest alive. 
