Seeley — Gravel and Drift of the Fenlands. 495 



that its depth seems not to have increased, as the lake waters by 

 themselves have little or no denuding powers. That after the 

 general featm^es of the country had been formed by marine denuda- 

 tion, and previous to the Glacial period, subaerial agencies may have 

 excavated part of the Rock-basin ; the drainage at that time finding 

 an exit through one or more subterranean passages : but that the 

 greater part of the ''Eock-basin" was cut out by ice; first, by the 

 movement of the ice-field that once covered Ireland, and afterwards 

 by the local glaciers, those of the valley of Lough Corrib and 

 Maum, and the transverse valleys. 



That the subaerial denudation was not since the end of the Glacial 

 period seems evident, for as before mentioned, all the rocks that can 

 be seen under the water are ice-rounded and scratched ; also the last 

 movement of this part of Ireland appears to have been upward, not 

 downward : ^ it might possibly have taken place in the Glacial age, 

 that is, after the ice-field ceased to move in one general direction, 

 but while glaciers flowed down the different valleys and slopes. 



V. — Theobetical Eemaeks on the Gkavel and Drift or the 



Fenlands. 



By Harry G. Seeley, F.G.S. 



Of the Woodwardian Museum in the University of Cambridge. 



1. Boulder -clay. 



THE cliffs of the Norfolk coast give conclusive evidence that, 

 before the denudation which formed the drifts had begun, the 

 level of Eastern England was not lower than it is now. On that 

 coast, at Weybourne, is seen the western end of a shell-bed which 

 holds the place of the Norwich Crag. But along to Hunstanton, up 

 the Wash, over the flat lands of Cambridgeshire, so little above the 

 sea-level, there is no trace of Crag, and no evidence that it was 

 ever there. At Norwich, and south and north, the Crag is covered 

 with thick gTavels, which do not appear to affect its preservation. 

 And hence it may be inferred that the absence of Crag in the Pen- 

 lands is, probably, due to something more than " moving accidents by 

 flood and field" The way in which the Forest-bed extends down to 

 the water side, and the bones dredged from it out at sea ; the 

 nature of the lacustrine deposit over it, and the fluviatile strata at 

 Mundesley, seem to show that before the Drift age came on, that part 

 of Norfolk extended further north. If the Crag was not formed in 

 the Fens or on the adjacent coast, it could only have been because the 

 sea had not access. What little is known of the laws of elevation 

 and subsidence of land does not favour a gratuitous assumption that 



* In places on the north shore of Galway Bay, peat with the roots of trees is 

 found below high water mark ; however, this does not prove that the land has sunk, 

 because, at the present day, about two miles west of Galway, between Blackrock and 

 Blake's Hill, there is a morass in which peat and trees are grooving. This latter is 

 divided from the sea by a barrier of sand and gravel, and in the places where peat is 

 now foimd below high water mark, similar barriers may once have existed. 



