UNDERGROUND WATERS OF NORTH-WEST YORKSHIRE. 25" 
The surface of the country is partly covered by mounds 
and ridges of boulder-clay and gravel of Pleistocene age, the 
product of a system of great glaciers which flowed round Ingle- 
borough from the high ground to the north of Ribblehead. 
The boulder-clays offering great resistance to the passage 
of water have in several instances considerably modified the 
courses of the streams both surface and subterranean, but as 
detailed reference will be made to these cases in Section III. 
it is unnecessary to discuss them at this stage. 
The glacial deposits have been described in the Geological 
Survey Memoir on the country round Ingleborough, and by 
Mr. J. G. Goodchild.* but the glacial drainage of the district 
has not been fully worked out as yet, and it is therefore impossible 
to come to any definite conclusions with regard to the direct 
effect of the glaciers themselves upon the subterranean streams. 
It can, however, be definitely stated that some of the exist- 
ing pot-holes and caves are of pre-glacial origin, while it seems 
possible that others which are now deserted by tlie streams, 
were produced during the glacial period by streams diverted 
from their original (and subsequent 0 course by the edge of 
the glacier, or by streams flowing off the ice itself. 
Further references to this most interesting topic will be 
made in Section III. 
In a country where not only the small tributary streams, 
but in some cases even the rivers themselves, pass underground 
for considerable distances, it is difficult to draw lines upon the 
map which shall represent the watersheds of the district, and, as 
the sequel will prove, if such lines be drawn by the ordinary 
method they will give erroneous results, since, in more than one 
instance, the water during its underground journey travels 
parallel or even counter to the slope of the surface, occasionally 
passing beneath a ridge to emerge in a neighbouring valley. 
In this way, water which, from its direction of flow and from 
the slope of the ground, would inevitably flow into the River 
Ribble if it continued its course on the surface, sinks into the 
* Notes on the Glacial Phenomena of Upper Ribblesdale. The 
Naturalist, August 1892. 
E 
