1869. ] SEARLES WOOD—BOULDER-CLAY. 109 
2. Down the valley of the Lune to Sedbergh, thence up the valley of the Raw- 
they, or up that of the Clough, and so over into the valley of the Ure. 
3. From Sedbergh up the valley of the Dee, and so over into the valley of 
the Widdale beck. and thence into Wensleydale. 
4. Down the valley of the Lune to below Kirkby Lonsdale, thence up the 
valley of the Greta and that of the Dale beck, over into the valley of 
the Gale beck, and thence over again into the valley of the Widdale beck. 
5. From the Gale beck up the Cam beck, and so over into Wharfedale. 
6. From the valley of the Greta (as in No. 4) up that of the Wenning, and 
thence either by the valley of the Anstwick beck, or that of the Fen beck, 
over into the valley of the Ribble, and thence over again into the valleys 
of various becks that are tributary to the Aire. 
In the first and second of these routes, the highest ground re- 
quired to be covered by the sea seems about 1200 feet, in the 
third and fourth it seems about 1500 feet, in the fifth between 
1200 and 1300 feet, but in the sixth there seems to be no barrier 
above 800 feet, while Stainmoor Pass is 1400 feet above the sea- 
level. The height of the top of Wasdale Craig (the original source 
of the boulders, according to Prof. Phillips) is marked on the 
Ordnance map as 1479 feet. 
The lowest of these several elevations would accord with the 
phenomena discussed in this paper, since it would place the chalk 
Wold below the sea-level. I conceive, however, that a considerable 
depth of sea-water would be necessary to waste the ice out of the 
valleys along the transit route previously occupied by the ice-sheet ; 
and until this was effected a floating transit could not take place ; 
but it is remarkable that, according to those who have studied the 
distribution of the Shap boulders, they do not seem to occur in 
Airedale, along which dale the route requiring the least submer- 
gence passes, and that it is by the more elevated route of Stainmoor 
that most of these boulders have come into the east of Yorkshire. 
These apparently conflicting phenomena, and similar phenomena 
attending the non-transit of the blocks over the watershed between 
the Lune and the Kent, referred to by Prof. Phillips*, appear to me 
susceptible of a satisfactory explanation by supposing the lower 
routes to have continued blocked by ice after a higher route by 
which the blocks have passed, such as Stainmoor, had become free 
from it, and so remained until the source of the blocks had be- 
come submergedt. If that explanation be the true one, it would 
seem to follow that, during the Postglacial emergence, no ice ex- 
isted in these parts adequate to the transport ef the blocks until 
after the lowest of these routes had reached the surface otherwise 
we should expect their transit by the lower routes to have occurred 
* See Report of Brit. Assoc. for 1864, p. 65. The Professor argues that the 
relative elevations of the country around Wasdale Craig must have greatly 
altered since the diffusion of the blocks, in order to reconcile the places of their 
occurrence. 
+ The depth at which ice floats would enable it to pick up blocks even after the 
parent source of them had become submerged ; and these, by the many turnings 
over and squeezings up which occur to floating ice, might become transferred to 
ice of so much less draught of water that they could pass even higher elevations 
than the original source. | 
