SEWELL : OVERFLOW CHANNEL IN NEWTON DALE. 447 
form the outcrop over a great extent of the moors, would soon 
succumb to the alternating action of frost and water, and would 
rapidly become, may I say, rotten. We have Rotten Gill, the 
name of a place near Goathland, as a present day description of 
this condition.* 
Those who have had the pleasure of reading Dr. Sven 
Hedin's account of the lakes and valleys of Northern Tibet, and 
his journe}'^ among them, will probably have a very correct 
description of the appearance and condition of the Jurassic 
ground surface when under the influence of the Norway ice. 
I do not speak now of what happened after the ice left, nor to 
the land under the ice-sheet, but of these soft series of shales, 
sands, and clays exposed to a climate which we may reasonably 
expect as correlative with the Ice Age. 
From data already established we are, I think, safe in 
concluding that the land sank as the Ice Age progressed. Possibly 
the sinking took place immediately^ before, but as I understand 
boulders are found on the bed of the filled-up old river valleys — 
without a depth of sand or earth, in layers, between the bottom 
and the boulders — it appears that the land sinking and the 
ice advance were at the same time. Later it rose to much 
above its present level ; this variation may have been as much 
as 200 feet. Since then it has again sunk in quite recent times. 
My strong opinion is that we have only to deal with one Ice Age, 
although its severity would wax and wane. 
Course of the Stream. Flo wing through Wheeldale Gill. 
This present branch of the Murk Esk rises on land about 
1,000 feet O.D. and flows through a valley bordered on either 
side by the 900 feet contour lines. Cooper Reed, in his " History 
of the Rivers of Yorkshire," gives a great importance to this 
stream, which he considers as a very old-time river. In this he 
is probably right, although its subsequent outflow into the Vale 
of Pickering through Forge Valley is, under the light of Professor 
* The Oxford clay would probably at this time cover a large extent 
of the higher Kellaways strata. A line of outliers of this series still exist 
■on the moors. This clay would weather even more rapidly than the 
Kellaways formation. 
