1870.] DE RANCE—LANCASHIRE AND CHESHIRE POSTGLACIAL. 667 
the alluvial plain, bounded by secondary banks, from 10 to 25 feet 
in height, depositing alluvium on the one bank and horizontally 
denuding the other. This secondary denuding, though important 
from being exercised along the whole course of the river, is of much 
less importance than that exercised at the elbows of the curves of 
the stream. 
I have gone thus at length into the origin of these cliffs, owing 
to Mr. Mackintosh having described them as haying been formed by 
the sea, and having, through misapprehension, represented me as 
holding that opinion. 
GENERAL ConcLUSIONS. 
1. After the deposition of the Esker drift, the country appears to 
have gradually risen, probably to an elevation of from 200 to 
300 feet higher than at present; but before this elevation was 
reached, a pause appears to have taken place, during which great 
denudation took place—the sea having eroded the cliffs of glacial 
drift in Western Lancashire and Cheshire, back and back, until the 
great low-lying plains, now covered with peat-moss, came into 
existence. 
2. At the present time, nearly two-thirds of the Ivish Sea is 
within the 30-fathom line, which runs on the east side, nearly in a 
straight line from the Mull of Galloway to St. David’s Head, passing 
to the west of the Isle of Man. The whole of this tract would there- 
fore become land if there were an elevation of 200 feet. Between 
this line and the coast of Ireland is a deep channel, generally about 
a mile broad, of an average depth of from 60 to 70 fathoms ; the 
deepest portions, or rather points, are off Magee Island, 84 fathoms 
(504 feet), and off Larne, 112 fathoms (672 feet): near this point is 
the Highland Rock, in the shallow called “ the Maidens,” in only 
6 fathoms, being a fall of 648 feet in half a mile. Off the coast 
of Galloway is a narrow channel, about 24 miles long; its deepest 
point is 149 fathoms, or 894 feet, opposite Belfast Lough. The 
deepest water in a straight line between Lancaster and Dundalk is 
57 fathoms (342 feet); between Dublin and Holyhead, 93 fathoms. 
This latter channel shallows to the south, towards the “line of 
least depth ” between England and Wales and Ireland, which runs 
in a curve pointing south, from the peninsula of Caernarvon to Ark- 
low, in Ireland, marking probably the watershed from which the 
rivers, which probably formed the long narrow channels occurring 
in the otherwise flat surface of the Irish Sea-bed, described above. 
Southward of this line, the deepest portion of which is only 44 fa- 
thoms deep (264 feet), the channels again deepen, increasing in depth 
towards the open sea, the average being about 60 fathoms. 
3. If in postglacial times the land rose as much as 280 feet above 
its present level, the coast-line ran from the Mull of Galloway 
to St. David’s Head, and Ireland was connected with Wales by 
a narrow isthmus over this ‘line of least depth,’ over which the 
postglacial mammals, the Germanic flora, and man himself may 
haye migrated. This connexion would appear to have taken place 
