On the Postglacial Deposits of Western Lancashire and Cheshire
Authors: de Rance C. E. 
Published: October 2009

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 Irish 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 therefore 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 Holy head, 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 Arklow, 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 fathoms 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 have migrated. This connexion would appear to have taken place after the formation of the lowland plains, and during a period when all the hollows in the much-denuded glacial deposits, both in Lancashire and in the Isle of Man, were occupied by lakes, which threw down the grey silt which I have called the “Lower
Cyclas
-clay,” and in which the
Cervus megaceros
is so often found entombed.

4.
It appears probable that glaciers still lingered in the deep valley of the Lake-district during the whole of the period occupied by the rising of the land, the pause, and its subsequent denudation and the connexion of England with the Isle of Man and Wales with Ireland. The climate would probably be rather colder than during the Esker-drift period, owing to the greater extent of land cooling the air; but the temperature, apart from local causes, was no doubt becoming warmer.

5.

At the close of the pause in elevation, before the lake-period, when the sea still occupied the low plains of Western Lancashire, the Shirdley-Hill sand and the Preesall shingle banks came into existence, forming a line of old sand dunes, from which sand was blown over the face of the country around Ormskirk, covering up the “lower peat” formed during the period of the pause. Below these old sand dunes in the plain, flats of this sand are occasionally found, forming the actual sea-bottom of the Shirdley-Hill-sand sea. The surface of the sand is worn, more or less, into channels by brooks, or small rivers, which no doubt flowed into the lakes, which, gradually increasing in size, afterwards covered the whole of these low-lying plains, not only between Liverpool and Southport, but between Fleetwood and Lancaster, and all the broad estuaries of the rivers flowing down from the Cumberland mountains, on the north side of Morecambe Bay, with the freshwater “lower
Cyclas
-clay.”

6.

During the formation of the
Cyclas
-clay, the entrance, or outlet, of all the river- and brook-valleys appears to have been choked and obstructed; for freshwater lacustrine marls almost invariably form the base of the alluvium of the valleys in Lancashire and Cheshire. On the surface of the day, on the plains and in the valleys, a forest of Scotch firs and oaks came into existence, the former sometimes appearing first, and being succeeded by the latter. The trees attained an immense size, owing probably to the continental conditions prevailing.

7.

The country began to subside; drainage became still more obstructed; the growth of peat ensued; the sea encroached upon the land, and gradually worked its way eastwards over the sea-bottom of postglacial times—a movement yet in progress, the lowland of Western Lancashire and Cheshire being preserved from it only by artificial means. In a few places the ground has, partly naturally, partly artificially, been reclaimed from the sea, as at the mouth of the Alt and Wyre, where it has deposited an Upper
Scrobicularia
-clay on the peat.

8.
Here and there, also, sand has begun to blow during the last three or four hundred years, the lines of sand dunes helping to keep the sea out. Everywhere the sand, when it first began to form, was blown into fresh water.