SECItKTAKV S |{ 1:F( >I{T. 
173 
Since the water passes beneath the river Ribble it follows 
tliat there 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 boring 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, no 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 as- 
certained 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 con.sisted of boulder clay, and that 
the bottom of Turn Dub consisted of boulders, the clayey matrix 
liaving been removed by the action of the flowing water. 
The boring operations were undertaken with a small sst 
of hand-boring rods provided with an augur bit. 
With this apparatus it was possible to prove that the bluish 
alluvial clay was underlain by a material consisting of a some- 
what sandy brown clay with many large stones, and in every 
Avay 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 carried more than a matter of one or two inches 
into the boulder clay, so that it was impossible to obtain any 
definite evidence regarding the thickness of the bed. 
Further, although boulder clay was proved to underlie 
the alluvium on both banks of the Ribble, it was impossible 
to obtain evidence of its existence in the river bed, as this 
