48 
HOWAiriMI : NOTKK ON HOULDER MARKINGS. 
Later, this tree outlet was interrupted by ice advancing 
across tlie Nortli Sea in a south-westerly direction, and sweeping 
down the coast of South Scotland. Northumberland, Durham, 
and Yoikshire in sucli force as to dam back the local glaciers, 
and to distribute their terminal moraines along the east coast, 
mixing them witli the Scandinavian locks which the inyading 
ice carried. 
To the foreign ice-sheet the east coast cliffs acted as a buffer, 
but its south-westerly trend enabled the coast line to deflect it 
southwards, and the British ice which reached the coast was 
dragged along with it. Where the coast line was lower it in- 
vaded the land for shorter or longer distances as the surface 
elevation (relative to the pressure of the ice-mass) controlled it, 
so that in north-east Cleveland it either forced its mass or some 
of its contents many miles inland, and again at Scarborough 
and in Holderness. 
Indentations in the coast-line, protected by cliffs witli their 
curves turned north-eastwards, acted as catchment basins for 
erratics, so that they are more plentiful in such places as Robin 
Hood's Bay, Scarborough, Speeton, Gristhorpe, the north side 
of Flamborough, etc. In such localities they occur in thousands. 
In many places the ice topped the cliffs, depositing boulder 
clays, while in others it failed to do so. 
The blocking of the mouth of the Tees compelled the Stain- 
moor and Teesdale glacier to leave its old course and to turn 
down the Vale of York, carrying with it its burden of Lake 
Countr}^ rocks. These are traceable all down the Vale of York 
as far as Escrick. They are also found at Doncaster, but it is 
not certain at present whether the Tees ice reached further 
south down the Vale of York than the two moraines at and 
near York. 
A line drawn from about Workington, on the coast of 
Cumberland, by the southern watershed of Thirlmere, and round 
to the west side of Wastdale Crag in Westmoreland, would appear 
to mark the boundary line or " boulder-shed " by which the 
Western group of rocks reached Yorkshire. Rocks north of that 
