260 UNDERGROUND WATERS OF NORTH-WEST YORKSHIRE. 
3. Methylene Blue. 
This substance was tried on several occasions, but was found 
to be useless for the jjurposes of the Committee, as it invariably 
failed to put in an appearance, although the same streams 
readily resj^onded when fluorescein was used. 
4. Fluorescein. 
This reagent, dissolved in a solution of potassium 
carbonate, has been found to be by far the most useful and 
trustworthy. 
Its appearance in a stream is unmistakable, except in 
cases where it is very dilute, and the stream is at the same time 
coloured strongly brown by peat. Even in this case, however, 
it can be detected by the practised eye, especially if there be 
bright sunshine at the time. 
During the last four years fluorescein has been the only test 
employed by the Committee. 
In a few cases the underground course of the water was 
actually followed, but in most cases this was found to be im- 
possible owing to the narrowness of the fissures. 
Accounts of such passages as it was j^ossible to explore 
will be found in the following pages. 
Since the work was commenced at Gaping Ghyll, it will 
be convenient to start the description at the same point. The 
arrangement of the following pages will on the whole, however, 
follow geographical rather than chronological lines, starting 
at Gaping Ghyll and working round by Alum Pot, Ribblehead, 
Chapel-le-Dale, and Ingleton. 
Gaping Ghyll. (P 3.)* [Pis. XXII. and XXVL] 
Fell Beck is formed by the union of three principal and 
several smaller streams at Fell Beck Head. The three larger 
streams rise as sj)rings on Simon Fell Breast, at a height of about 
2,100 feet O.D. 
* The figures given in round brackets refer to the accompanying plans 
and mapi".. "P" signifies Pot-hole or water sink, and "S"i3 used to 
indicate Spring. 
