the Estuary of the Mersey. 113 



period, also flowed down a deep valley now silted up; and, as its 

 mouth now bottoms on the Boulder-clay, and the river is nearly 

 empty at low water, after the silting up, it must have worked its 

 course to the westward and cut out the cliffs of Boulder-olay forming 

 its west or left bank at Hesketh. The valley of the old Wallasey 

 Pool, that of the river Weaver, and numerous tributaries along the 

 Mersey, now silted up, all go to prove that the land was, previously 

 to the Post-Glacial deposits, considerably elevated, as these valleys 

 could only be cut down vertically by sub-aerial action ; though, I 

 believe, they have been considerably widened and modified by marine 

 denudation, 



Washed-Brift Sand. — Evidences of a very considerable submer- 

 gence of the land are tolerably abundant in districts adjacent to the 

 one under consideration, marine shells having been found in stratified 

 beds of sand and gravel up to 400 feet high on the Eibble, 1200 feet 

 at Macclesfield, and 1300 feet on Moel Tryfaen in Wales ; on the 

 opposite side of the Irish Sea on the Three Kocks Mountain, at 

 Kingston at 1200 feet high, and I believe, also, in elevated positions 

 in the Isle of Man. These shells consist wholly of recent species, 

 but some of them are of a northern character, indicating colder con- 

 ditions than at present obtain. Their exact position in relation to 

 the Boulder-clay of Lancashire has not yet, that I can ascertain, been 

 clearly made out, and demands much closer attention than has hither- 

 to been given to the question. Judging from the physical appearance 

 of Lancashire and Cheshire, I have slowly arrived at the opinion that 

 since the laying down of the Boulder-clay, it has been elevated and 

 again submerged, as its surface presents what can only be planes of 

 marine denudation.^ While, on the other hand, the valleys before 

 alluded to, now filled up with Post-Glacial deposits, and also the 

 main valley of the Mersey, had, undoubtedly, been excavated their 

 full depth before any of these Post-Glacial depositions took place. 

 The width of these valleys is too great, and the slopes of their sides 

 too gradual, to be due to sub-aerial influences alone. Nor could 

 they, in my opinion, have been formed during the first emergence of 

 the Boulder-clays from under the sea, as I fail to understand how, in 

 that case, they could have been cut down to their present depth. A 

 considerable Post-Boulder-Clay submersion of the land, previous to 

 any of the deposits I am about to describe, has, therefore, I venture 

 to think, taken place. Whether this interval of elevation and sub- 

 mergence is accepted or not, the Boulder-clay has, undoubtedly, 

 suffered much marine denudation, and the effect has been the elimina- 

 tion from it of what I have termed, in allusion to its derivation, 

 IV ashed- drift sand, imder which term I include the Shirdley Hill 

 sand of De Eance^ and the upper drift sand of local geologists. 

 Possibly the forest sand of Binney ^ and the superficial sand described 



^ Chambers calls them terraces. See Ancient Sea Margins, p. 224. 

 ^ Explanation of Geological Map, 90 S.E. 



2 " Drift Deposits of Manchester and its Neighbourhood." — Manchester Literary 

 and Philosophical Society's Memoirs, vol. yiii. 



VOL. IX.— NO, xcui. 8 



