64 THE DALES OF DERBYSHIRE. 
by 19 miles long. From these figures we may gather some 
idea of the enormous wearing power of carbonated water on 
limestone rock, and did we know the solid contents of the 
Dove Valley from where the limestone begins, and the 
average amount of water running through it from the 
beginning, we should have little difficulty in estimating the 
time it took to excavate the Dale. 
