258 UNDERGROUND WATERS OF NORTH-WEST YORKSHIRE. 
limestone, passes into a tributary of the Wenning and so eventu- 
ally joins the River Lune. 
It may be mentioned that the terms " pot " and " pot 
hole " are used locally to signify the deep chasms down which 
the surface streams plunge, while the terms " enters," " shake 
hole," " water swallow " are used indifferently on the Ordnance 
Maps to indicate smaller openings of a similar nature or even 
those funnel-shaped hollows otherwise known as swallow-holes, 
which are such a well-known feature of all moors with limestone 
below the surface soil. 
III. The Underground Waters. 
In the earlier years of the investigation, the work was 
•arried on by large parties of Avorkers, who assembled at some 
point in the district and proceeded to investigate a number 
of streams simultaneously. 
This was accomplished by the use of various test substances 
introduced at the water sinks. A watch was then set at all 
the springs which were thought to be possible outlets. 
As some of the substances employed were not visible in 
the springs, but could only be detected by means of chemical 
reagents, it was necessary to collect samples from a large number 
of springs at frequent intervals. 
The labour involved in the collection of samples and the 
subsequent examination was so great (1,200 tests were made 
during a single season) that it was decided to employ colouring- 
matters only, as these could be readily seen in the field, and 
so the work of watching was minimised and that of testing 
entirely obviated. 
This, of course, reduced the number of streams which could 
be treated simultaneously and consequently largely increased 
the time necessary to complete the work ; but at the same 
time it became possible to employ much smaller working parties 
with the result that the meetings could be held more frequently. 
When the main lines of the underground drainage had been 
determined, it became possible to work several streams at once, 
provided these were chosen sufficiently far apart to exclude 
