C. E. de Ranee — Pre- Glacial Geography of N. Cheshire. 161 



valleys, and the subsidence of the land, its seaward margin was 

 exposed to marine denudation at the period of the formation of the 

 Birket plain. 



It therefore appears probable that in pre-Grlacial times a plain of 

 marine denudation composed of hard and soft beds of New Eed 

 Sandstone existed from the borders of Wales to south-western Lan- 

 cashire,^ unbroken by valleys, over which flowed the Dee to the 

 north, receiving as a tributary from the east the Mersey, which 

 gradually cut for itself a transverse gorge across the strike of the 

 rocks ; at the same time, longitudinal valleys to the north and to the 

 south, gradually came into existence. Those to the north were 

 afterwards entirely destroyed by Marine denudation, which formed 

 a lower plain. The subsidence continuing and the climate becoming 

 glacial, the district was submerged beneath the waters of the Glacial 

 Sea, and the Gorge, or transverse valley, as well as the longitudinal 

 valleys, were filled up with Glacial deposits. Afterwards, on the 

 re-elevation of the country, these were excavated out, partly by 

 running water, and partly perhaps by small glaciers which, as I have 

 attempted to show elsewhere, midoubtedly held their ground, at the 

 close of the Glacial epoch, in the valleys of the Lake-district. The 

 entire valley of the Mersey, including its termination through the 

 Wallasey Gorge, would be equally filled up with Drift ; over this 

 surface of Drift the river must have flowed, widening and deepening 

 its channel as it ran, here making great cliffs of overhanging 

 Boulder-clay, and there cutting through the Drift, down to the bare 

 rock, and in some instances cutting its bed wider and deeper in the 

 rock than it was before the Glacial submergence. 



In the clifis on the south side of the Mersey, near Eastham, the 

 base of the Glacial Drift, resting on the rock, is more than twenty 

 feet above the present base of the cliff, which is slightly below high- 

 water mark. The river is now wearing this cliff back and back 

 into the gradual slope of the old pre-Glacial valley, which appears 

 to have had its deepest hollow near the opposite bank on the Lan- 

 cashire side of the river ; near the Otter's Pool the base of the Drift 

 is rather below high-water mark, the rock only forming the strand 

 between tide-marks. The rock-surface is also below high-water 

 mark on the west coast of the peninsula, where the banks of the 

 Dee are formed of Boulder-clay, more or less from Hoylake to Park- 

 gate and Neston. Near Hoylake a submarine ridge of rocks occur, 

 Bunter pebble-beds thrown up by a fault, culminating in Hilbre 

 Island. Between the ridge and the Cheshire coast there is a channel, 

 and from the ridge to the opposite coast of Wales the rock surface 

 descends to a great depth, and the Glacial beds are much denuded, 

 and are covered up by an immense thickness of alluvial silt resting 

 on peat, the silt reaching, I believe, a thickness of 60 or 70 feet. 

 It has been penetrated in boring for coal, which has been found to 

 lie under the western side of the estuary of the Dee. 



The bed of the Mersey from Euncorn Gap to the sea is excavated 



1 And of course much further, but iu the above notes the country around the 

 mouth of the Mersey is alone considered. 



VOL. VIII. — NO. LXXXII. 11 



