438 SECTIONAL TRANSACTIONS.—C. 
That the estuary of the Dee has existed in approximately the same position 
since early Pleistocene times is highly probable, for borings have revealed the 
fact that Boulder Clay extends far below sea-level under parts of it. It 
appears, however, that the post-Glacial estuary does not exactly coincide with 
that which existed before the Glacial Period, and that the pre-Glacial course 
of the river after it left the Welsh hills was not recovered after the ice 
retreated. ‘The changes in the upper reaches have been investigated by Mr. 
L. J. Wills (Quart. Journ. Geol. Soc., vol. Ixviii., 1912, p. 180). Lower down 
at Holt, Alford, and Chester, as shown in the Geological Survey Memoir on 
Flint, 1890, p. 161, the pre-Glacial course was so blanketed by Boulder Clay 
that the river cut a new course, partly in solid rock. A depressed area ranging 
through Pulford, Kinnerton, and Dodleston, presumably marks the site of the 
buried valley, and leads to a tract on the south side of the modern estuary, 
where Boulder Clay has been found to extend to a great depth below sea-level. 
Similar changes seem to have been forced upon the Mersey as a result 
of glacial conditions. One diversion near Runcorn was made known by 
Mellard Reade, who showed that the pre-Glacial course ran north of Westbank 
under Ditton Marsh (Proc. Liverpool Geol. Soc., 1871-2). He was led to 
anticipate that a pre-Glacial channel would be encountered in the Mersey 
Tunnel, as proved to be the case (op. cit., vol. v., 1889, p. 74). In several 
other places also along the present course of the river great depths of Boulder 
Clay, sometimes far below sea-level, were recorded by him and others. It 
would not be safe, however, to assume that all the cases of deep drift are 
referable to the pre-Glacial channel of either the Mersey or the Dee. The soft 
Triassic rocks were deeply scored, and yielded vast quantities of the material 
which was carried southwards to form the glacial drift of Cheshire; shallow 
rock basins, as well as river channels, may lie buried beneath the glacial drift. 
The changes which have taken place in post-Glacial times are of a different 
character, and due to a different cause. Evidence is furnished by buried land 
surfaces on the Lancashire, Cheshire, and North Wales coasts that the land 
has stood at a higher level in post-Glacial times than now. In South Wales 
the difference in altitude was ascertained to be not less than 55 feet (Quart. 
Journ. Geol. Soc., vol. lii., 1896, p. 474), and the occurrence of polished flint- 
implements proved that one at least of the submerged surfaces was of Neolithic 
age. The deposits of this age lie in and below the present foreshore, and 
extend inland under the recent alluvial deposits of the valleys. | Wherever 
exposed to the scour of the tide they are being rapidly swept away, and the 
assumption that they once extended far beyond their present limits is not only 
legitimate but supported by tradition, whatever that may be worth, concerning 
lost lands off the coast of North Wales. We may assume, therefore, that the 
coast was fringed by a low-lying forest-grown tract, and that the estuaries were 
bordered by similar uninviting ground. Sinking of the land and the sub- 
mergence of these tracts were the first stages in the development of the estuaries 
as we see them. The admittance of the tide led to the further stages. 
So far, however, we have found no good reason why the Dee was preferred 
to the Mersey by the early settlers. More than one hypothesis has been put 
forward to account for the preference. It has even been suggested that the 
Mersey estuary had no existence in Roman times, and that the river then 
formed a tributary of the Dee. The second-century maps of Ptolemy show 
what is witheut doubt the estuary of the Dee, but represent no estuary corre- 
sponding to that of the Mersey. Further support for the suggestion was found 
in the existence of a valley which runs near Stoke from one estuary to the 
other. That such a valley exists is true; it is, moreover, occupied by a con- 
tinuous strip of alluvium which connects the alluvium of the Gowy, a tributary 
of the Mersey, with that of the Dee. The theory that it formed a free passage 
for the Mersey is founded on the continuity of the alluvium, on the occurrence 
of marine shells of recent species along it, and, lastly, on the authority of a 
map of the time of John Scott, eighth Earl of Chester, 1232-1237, in which it is 
represented as being occupied by water for its whole length from the Mersey 
to the Dee. These arguments, however, are worthless, for the alluvium, 
though continuous, forms a gentle slope rising to a height of 40 feet above the 
sea. A subsidence sufficient to submerge this slope would put under water 
