430 CARTER : GLACIATION OF DON AND DEARNE VALLEYS. 
This would cause the impounding of the whole northerly drain- 
age as far as Bretton, and would have united the three lakes 
into one large lake. This would have been an impossibility unless 
an outlet existed to carry off the overflow. No such valley was 
up to that time known to me, but the six-inch maps of the Went- 
wortli area being obtained, a cut was found through the 350-foot 
