MOVEMENTS OF UNDERGROUND WATERS OF NORTH-WEST YORKSHIRE. 225 



The Secretary was informed by Mr. Wilcox, of Selside, that the 

 fluorescein mentioned above had been seen in Footnaw's Hole prior to its 

 appearance at Turn Dub. 



The relative positions of Long Churn, Alum Pot, Footnaw's Hole, 

 and Turn Dub will be seen by reference to the map (Plate II.). 



In dry weather Footnaw's Hole appears as a wide cleft in the lime- 

 stone, with sloping banks of silt and sand round two sides and precipitous 

 limestone rocks on the other two. When the streams are in flood after 

 hea\-y rain or during the melting of snow the water in Footnaw's Hole 

 I'ises to the lip and liows over down Footnaw's Beck into the Ribble. 



Turn Dub is very rarely dry, while it is only in exceptionally wet 

 weather that water flows from Footnaw's Hole. 



Thus it would appear that Footnaw's Hole is a flood outlet, and only 

 comes into operation Avhen the underground passage leading to Turn Dub 

 is full and therefore unable to take the excess of water. As the lip of 

 Footnaw's Hole is just below the 1,225-foot contour, and Turn Dub just 

 below that of 1,200 feet, there cannot be a fall of more than 25 feet from 

 the former to the latter. 



Further, since in ordinary weather, when the stream is issuing 

 from Turn Dub only, the water in Footnaw's Hole stands some 20 feet 

 below the ground level, it will be seen that there must be a siphon-like 

 passage below the river ; and since this passage must be constantly filled 

 with water up to the level of the overflow of Turn Dub, it will account 

 for the very slow passage of the fluorescein over at least this part of the 

 journey. 



Since the water passes beneath the River Ribble it follows that theie 

 must be some impervious cover, because if this were not the case the 

 water of the underground stream would find an escape at the lowest 

 point— namely, in the bed of the river— and would not, as is the actual 

 case, pass under that stream and rise some 10 or 12 feet above it on 

 the opposite bank. 



With a view to ascertaining the nature of this impervious cover and 

 its thickness it was determined to carry out a series of borino- operations 

 in the alluvial flat between Turn Dub and the river. ° 



In the first place Turn Dub was sounded and found to be only about 

 18 feet in depth. Now Turn Dub is a circular pond of still water, and 

 although a large stream of water flows out there is no disturbance of the 

 surface, nor welling up of the water apparent. This would lead one to 

 suppose that the pool was much deeper than is actually the case. So far 

 as could be ascertained by drawing the sounding-iron across the bottom 

 of the pool, this consists of large boulders. This led your Committee 

 to suspect that the cover consisted of boulder clay, and that the bottom 

 of Turn Dub consisted of boulders, the clayey matrix having been re- 

 moved by the action of the flowing water. 



The boring operations were undertaken with a small set of hand 

 boring-rods provided with an auger bit. 



With this apparatus it was possible to prove that the bluish alluvial 

 clay was underlain by a material consisting of a somewhat sandy-brown 

 clay with many large stones, and in every way similar to the boulder clay 

 of the neighbourhood, which in some places can be seen close to the river- 

 bank. 



_ The presence of numerous boulders prevented the boring operations 

 being earned more than a matter of 1 or 2 inches into the boulder 

 1902. Q 



