378 
ELGEE : GLACIATION OF NORTH CLEVELAND. 
Looking for an outlet in a northerly direction, the Sower- 
dale overflow could only have escaped into t]ie Guisborougli 
Valley at a time when tlie Slapewath overflow had ceased to 
operate and when a free outlet allowed the drainage to escape 
to the sea at Saltburn. All the phenomena of Skelton Beck 
are well below 350 feet, and if the ice readvanced and blocked 
up Kildale again, after the Vale of York drainage had ceased, 
we should have had the impounded drainage cutting across Castle 
Hill and forming Sowerdale. At a later stage the overflow, now 
the Leven, escaped in the manner described by Mr. Hawell, 
since at the foot of Easby Wood it persistently refuses to take 
a more direct and much lower course towards the south-east, 
showing the presence of an ice barrier. Hence the probability 
is that Kildale may have been blocked up for a l>rief period by 
a readvance after the coast as far north as Saltburn was free 
from ice.* 
This readvance would also account for the fact that no signs 
are left of any channels out of Kildale in alignment with the 
Vale of York drainage system. Mr. Kendall expressly states : — 
" The ice front must have stood across the Bocsbeck Valley 
until the Slapewath Gorge was lowered below the level of the 
drift barrier across Boosbeck — that is to say, beloAV 425 O.D. 
From this clue it is possible to define some of the further course 
of the stream and consequently of the ice front. It will be 
remembered that the overflow channel into Eskdale by way 
of Kildale is at an altitude of 580 feet, therefore it is quite certain 
that there must have been a line of drainage open into the Vale 
of York (p. 566)." Now the sequence of overflows connected 
* With regard to Sowerdale, Professor Kendall has kindly furnished 
me with the following note : — " I am very doubtful whether the Sowerdale 
Valley could be regarded as a lake overflow. The arrangement of the 
contours does not suggest erosion by a large stream, for it seems too wide 
and too steep at the head. It is of the type of Bridle Gill (north of Rose- 
berry Common). A stream that could cut a valley of such breadth wo\ilrl 
have eroded its floor in a broader notch, and have obliterated all signs 
of the flow towards Kildale. Experience gained in the last two years 
has made me suspicious of cases of apparent flow in opposite directions 
through the same channel. It is easier to assume that a transverse water- 
shed or " corrom " has been prodiTced by inflow by a lateral stream, or by 
some similar means." Even if we reject Sowerdale as an overflow, the 
anomalous course of the Leven has still to bo explained, so T have lot 
the above-given explanation of its origin stand.. 
