432 
(LARK: GLACIAL SECTIONS 
shaped, but facing more easterly. The whole length of 14 miles 
naturally suggests the Scotch Eskers, There are, moreover, 
other elevations parallel to it. On the west bank we have the 
gravel-capped ridge stretching to Bishopthorpe, and the broken 
line from the new water works, one mile above York, through 
A comb and Askham Bryan to Askham Richard. In the two last 
districts, however, it is little but a capping on the Triassic beds ; 
and near the Ouse all three ridges are lost in the irregular series 
of elevations parallel to the river. 
Turning to the other point, — the remarkable bubbling, — the 
following is, perhaps, the most probable explanation. As we have 
seen, the sand-beds are very disconnected, and bed C especially, 
was evidently cut off upwards. Shaft V. seems to have tapped it 
near its highest point. It was covered by thick impervious 
boulder clays. Their impenetrability in most parts was indicated 
by the yard of remarkable dry, crumbly clay above the sand. 
The wet from above could not descend as fast as the air forced in 
from below absorbed the moisture. Probably the sand-bed was 
like a closed cistern, with entrance and exit apertures low down, 
the former being the more commodious. In dry seasons, however, 
the exit would drain off the water collected in the sand-beds, and 
this water would be replaced by air. In wet seasons — such as 
the winter and spring of 1876 — water would collect faster than 
the exit could remove it ; or perhaps the line of saturation might 
rise above the point where both entrance and exit apertures lay. 
In either case the air in the sand-bed above, having no means of 
escape, is subjected to pressure by the rising water, the amount 
depending upon the height of the line of saturation at the water 
level in the sand-bed. Under this pressure the air slowly forced 
its way up through the superincumbent clays, which thus grew 
dry and crumbly. When the sand was tapped near the summit 
of the bed at shaft V., this air was blown out from the sand by the 
rising water, with a pressure, probably, of several pounds to the 
square inch. For the line of saturation was at the time at least 
