GOODCHILD : GLACIAL PHENOMENA OF UPPER RIBBLESDALE. 243 
bottom strata to such an extent as to neutralize the effects of 
terrestrial radiation. Farth-heat, therefore, keeps the lower strata of 
the ice at a higher temperature than that of the strata above; and 
therefore causes the ice near the bottom to expand to a larger volume 
than do the colder layers nearer the surface. In that way the 
different expansion gives rise to a differential movement of the mass, 
in which the parts most warmed by the earth-heat radiating from the 
rocks at the bottom of the valley move faster than those contracted 
by the lower temperature prevailing nearer the surface. 
a differential movement is set up, part, at least, of the energy is 
converted into heat, and in that form cick ‘the movement still 
more, I have long felt that, in basing our conclusions regarding 
glacial phenomena upon what facts can be gleaned from a study of 
the tiny glaciers still surviving in the Alps, we were in danger of 
falling into very serious error. And so we have done, and our 
progress towards a right understanding of our subject has been 
retarded accordingly. 
The next point to consider brings us nearer to glacial matters of 
more local interest. There is now quite enough known about the 
direction of movement of the larger flows of ice at the climax of the 
Glacial Period to warrant us in coming to the following conclusions 
regarding these matters in the North of England :—Three or four 
large areas in this part appear never to have been invaded by ice 
carrying boulders foreign to their own drainage area. One of these 
te 
Wear. Another includes the greater part of the Lake District. Next 
is the area extending eastward from the Howgill Fells to Richmond, 
northward to Stainmoor, and southward to Craven. Further south 
comes the upland area ranging to the Peak of Derbyshire. To 
these may be added the Cleveland Hills. The second and the 
third are all that concern us in the present connection. Within 
these there ranged a zone of ice-shed whose general direction, as we 
trace it from the west eastward, may be approximately defined 
thus :—In South Cumberland it followed very nearly the line of 
highest ground up to about the head of Derwentwater, that is to say, 
a north-easterly direction. Thence it curved round to the south-east, 
passing through Wastdale Head, through the Howgill Fells, across 
Wilbert Fell, and eastwards by the head-waters of the Swale and 
Yore. Beyond this the line cannot be defined even approximately. 
To the north of that line of ice-shed the boulders travelled at first 
north-westward ; and then, when the Solway ice began to flow inland 
and uphill, it Gens: in a generally easterly direction, over Stainmoor, 
past Barnard Castle, and out to the maritime parts of Yorkshire. 
August 1892. 
