HUGHES : INGLEBOROUGH. 
139 
after the impervious shale has been cut back far from where it 
extended when the hole originated. But, as a rule, the first set 
of holes is deserted and left dry when, by the cutting back of 
Fig. 3. 
GROUND-PLAN SHOWING MODE OF WEATHERING OF MOUNTAIN LIMESTONE. 
(1 inch = 2 feet 8 inches.) 
\^By permission from the Quart. Journ. Geol. Soc, JNTof. 1886.} 
the impervious beds, the streamlets gain access to an inner circle. 
Thus row after row of such holes remain witness to the constant, 
though intermittent, recession of the impervious beds on which 
the water collected that formed them. 
