Palwo-Geological and Geographical Maps of the British Islands. 291 
Representative Post-pliocene Serves—continued. 
Lancashire, Cheshire, &c. East Anglia. 
Sand and rolled gravel with shells.* 
Earliest Glacial Beds represented in the north of Contorted Drift with masses of Marl and Chalk. 
England and Scotland YW the “True Till,” with 1 Boalioe Clay with Erratics.t 
Fresh-water Beds, . | Laminated Blue Clay. 
| Flv'via-marine Sand and Clay. 
2. “Forest bed of Cromer.” 
(1. Sand and Gravel with Loam (Norwich Crag). 
Chalk. 
Pre-glacial Beds, 
Taking a general view of the subject, it must be supposed that the glacial and 
sub-glacial beds overlying the forest bed of Cromer were the precursors of the great 
land ice-sheet, represented by the Great Chalky Boulder Clay, and that the marine 
gravels overlying the Purple Boulder Clay are the representatives of the middle 
sand and gravels of Cheshire, Lancashire, Wales, Wicklow, and Wexford.t 
The beds formed during the interglacial stage above described are widely distri- 
buted, consising of sand, gravel of water-worn pebbles, and beds of loam, generally 
finely laminated ; they give evidence of deposition under water. The occurrence 
of sea shells in various parts of the British Isles, proves that this water was the sea, 
and the genera and species vary somewhat according as warm or cold currents were 
present. Sometimes the gravels are found resting directly on the Lower Boulder 
Clay, as at Howth and Killiney, in Ireland, on the banks of the Ribble, near 
Preston, and in East Anglia. In other places they rest directly on the solid floor 
of the older rocks. They also cover large tracts of the central plain of Ireland, 
ascend on the Wicklow mountains to an elevation of 1,235 feet, as shown by the 
Rev. Maxwell Close, and occur along the eastern coast of Ireland, often overlaid by 
the Upper Boulder Clay. Amongst the Sperrin mountains in Ulster they have 
been found by Mr. Joseph Nolan at an elevation of 1,200 feet. Amongst the 
mountains of North Wales they have been detected by the late Mr. J. Trimmer,$ 
by Mr. D. Mackintosh and others at somewhat higher elevations, and by Professor 
Prestwich on the hills near Macclesfield, at an elevation of about 1,100 to 1,200 feet.|) 
They are spread over large tracts of Lancashire, Cheshire, and Salop, sometimes 
occurring at the surface, but as often concealed beneath the Upper Boulder Clay. 
Tn the central counties they are extensively distributed, and on the tableland of 
the Cotteswold Hills of Gloucestershire and Oxfordshire, I have traced them to 
* Mr. Woods’ “ Middle Glacial Beds.” 
+ Mr. Woods’ “‘ Lower Glacial Beds.” 
} The presence of /usus contrarius, and two or three other forms supposed to have been extinct, but 
re PORE | in the Suffolk Crag, induced the late Professor Edward Forbes to refer the Wexford gravels 
to the age of the Crag, but this shell has recently been dredged up off the coast of Spain as a “living” 
form. Professor Haddon has shown me a specimen from the collection of the Royal College of Science, 
Dublin. 
§ On Moel Tryfaen at 1,360 feet. The shells have subsequently been named by Mr. R. D. Darbyshire. 
|| Lyell, Zoid. p. 317. : 
Ps Be 
