KENDALL : THE GLACTATION OF YORKSHIRE. 
313 
great beds of sand and gravel without disturbing the bedding, or 
even overturning the standing trees which had been smothered on 
the original advance of the ice. Even in the Alps, however, cases 
are not unknown of glaciers moving over their own terminal moraines. 
"When we come again to the question which is the older, the York 
or the Esciick moraine, I confess myself unable to decide. I think 
both may l ave been overridden by oscillations of the ice-front, but 
whether by halts in the advance or of the retreat I am unable to say. 
These are points which might fitly receive the attention of the geolo- 
gists of the county, and I am content to have suggested that the rela- 
tive positions of two moraines are not absolute criteria of relative age. 
Another problem connected with the Vale of York glacier concerns its 
furthest extension. Shreds of boulder clay are mapped along the 
"Wold escarpment for a long distance south of the Escrick moraine, 
and here and there great patches of gravel as at Heck rise out of the 
monotonous expanse of " warp." Are these relics attesting a great 
extension of the glacier to the southward, or are they, as seems to 
me very improbable, the deposits of an extra-morainic lake ? I am 
not in possession of facts enabling me to attempt a full explanation 
of their occurrence, but I shall say something more regarding them 
on a later page. 
I must now apply myself to the discussion of the causes which 
modified the ice-flows so as to effect the distribution of Shap erratics 
in the two southerly streams, viz., those down the Yorkshire Coast 
and the Vale of York respectively. The former of these shows that 
the Stainnioor glacier had a free outlet to the sea at one time, and 
one would in that case expect that it would keep to the Valley of 
the Tees and not encroach to any great extent upon the Vale of Y ork. 
Mr. Lamplugh has, however, described some peculiarities in the 
vertical distribution of erratics through the drift series of the coast, 
which suggest, or perhaps prove, that the mouth of the Tees during 
some portion of the glacial period was obstructed so as to prevent 
the escape of the glacier in that direction. The occurrence of great 
numbers of erratics of Scandinavian origin in the drift of the east 
coast, from Whitby to Cromer, raises a strong presumption in favour 
of the extension to the British shores of that great ice-sheet which 
