,20 S. V. Wood,Jun. — Sequence of Glacial Beds. 



Lincolnshire. This limited and localised re- submergence, it will be 

 observed, was not only posterior to and unconnected with the great 

 Glacial submergence, but seems to have been confined to the more 

 Northern part of England.^ What length of time was involved in 

 the progress of this great and original emergence, I will not venture 

 to estimate ; but it can scarcely have been otherwise than con- 

 siderable ; and it is one which, by assigning to it certain fossiliferous 

 gravels, may, I think, afford us an exit from many difficulties. 



We are naturally too apt to estimate the duration of Geological 

 "time by the amount of deposit formed in any period, whereas 

 probably the longest lapses have been those of which we have no 

 representation, in the shape of deposits, in this country. As Mr. 

 Darwin has said, it is during submergence that deposits accumulate ; 

 while during emergence their destruction is the principal thing that 

 takes place, such accumulations as do form at this time being of 

 limited extent and sporadic in their distribution. 



Adding to the time thus occupied in this great emergence and 

 denudation that which, subsequently to the North-East of England 

 having completely emerged, was occupied in its partial re-submer- 

 gence and recovery therefrom, and to this again adding the period 

 during which our river-gravels and brick-earths, without Cyrena 

 fluminalis, were accumulating — a period in which very considerable 

 changes in the mammalian inhabitants of this country took place — ■ 

 and we shall, I think, find ample scope for supposing that the Post- 

 glacial period (as previously defined) may have equalled, if even it did 

 not exceed, in duration the Glacial. 



Let us now examine the features which the MoUusca yet obtained 

 from the various beds present. The pebbly sands of Belaugh and 

 Eackheath, in Norfolk, to which Prof. Harkness refers as underlying 

 the Lower Boulder-clay of that county,^ are those from which the 

 Lower Glacial shells have been procured by Mr. Harmer and myself. 

 They have yielded thirty-five forms of Mollusca. This sand, though 

 continuous with the pebbly sand underlying and interbedded with 



* Ho-w far it may have extended into Scotland 1 know not ; but, while the central 

 parts of England do not appear to have participated in this partial re-submergence, it 

 is important to observe that the evidence seems to me clear that all the South of 

 England, as far as the Northern limit of the Thames gravel formation, except the 

 higher parts of the "Wealden dome, had not, at the time of which I am speaking, 

 emerged from the original Glacial depression, but was being denuded under the 

 influence of those submarine disturbances which began by breaking up the Thames 

 gravel formation, and terminated with the elevation and complete denudation of the 

 Weald valley. It seems reasonable to suppose that the partial re-submergence of 

 the North-East of England was the result of this elevatory activity in the South, by 

 way of counterpoise, and that dui'ingit the Cyrena fluminalis occurring in the Thames 

 gravel formation, and in the bed c, and not known as a Glacial shell, died out in this 

 country. 



^ This term, " Lower Boulder-clay," is very objectionable and illusory ; for not 

 only are there several Boulder-clays, but the so-called Lower Boulder-clay of Cromer 

 (part of li) is not the bed called Lower Boulder-clay at Norwich, which is the con- 

 torted drift, (7, that overlies h on the Cromer coast. On the other hand, if I am 

 right in my deductions, the bed, c", which is the uppermost in East Anglia, is the 

 lowest Boulder-clay in Yorkshire ; the bed h, which 1 regard as uo part of the Glacial 

 series at all, being the uppermost Boulder- clay of this county. 



