the level of the river bed. In 
another case a little further 
from the river bank a bore 
hole reached a depth of 14 
feet when it became blocked 
by a boulder, the wliole of 
this bore hole being in 
boulder-cla}^ the limestone 
floor not being reached. 
The Ribble can be seen to 
be flowing over drift, no 
solid rock being exposed for 
^ nearh^ two miles above 
S Turn Dub or 300 yards 
below it. 
H As has been shown, the 
^ water in Alum Pot is nearly 
2 on the same level as that 
s at Turn Dub, while the 
:3 two are connected by a 
s passage constantly filled 
S with water and at a lower 
§ level than the outlet (see 
I Fig. 6). 
It is difficult to see by 
what means such a passage 
could be eroded unless there 
was formerly an outlet at a 
lower level than the present 
one. 
Since the present bed 
of the liver is excavated in 
boulder-clay it follows that 
the pre-glacial bed must be 
at a lower level than the 
present one, but has not 
yet been cleared of glacial 
drift. 
