400 Mr. S. V. Wood on the Belgian Equivalents of 



cut through or exist in the Loess itself. If, therefore, the Boulder- 

 clay or upper Drift of England has been acted upon by move- 

 ments which have similarly affected the Loess of Belgium, it 

 follows that both deposits had been thrown down before these 

 movements began. It can be shown that these movements 

 have not affected the postpliocene gravels that rest on surfaces 

 from which the upper Drift has been denuded *, so that they 

 must have originated prior to these gravels having been depo- 

 sited ; and since, from the great area over which the denudation 

 has extended, we can attribute it to nothing but the action of 

 the sea, we must assume either that it resulted during an emer- 

 gence of the bed of the upper-Drift sea, or that a second general 

 submergence and elevation took place. Although the evidence 

 collected by geologists appears to me to indicate that parts of the 

 south of England and of the north of France have been sub- 

 merged (and that violently), and still further denuded, subse- 

 quently to the general disturbance and denudation produced by 

 these circular phenomena, and subsequently to the area having 

 been converted into land, yet there is no trace of any second 

 general subsidence and elevation. It therefore seems to me 

 that we have no alternative than to infer that these circular move- 

 ments originated under the upper-Drift sea ; and in that case, as 

 the Loess is disturbed by those movements, it must have been 

 deposited prior to the elevation of the bed of that sea. 



In describing the lower Drift of the Eastern Counties, I dwelt 

 upon the mode in which the position occupied by it relatively to 

 the lower tertiaries indicated that the bay depositing it advanced 

 inland by erosion as much as or more than by depression — differ- 

 ing entirely in this respect from the overlying Boulder-clay. 

 The latter in the east of England, where not denuded, spreads 

 evenly over the Eocene tertiaries which the lower Drift had not 

 reached, and over the cretaceous and oolitic deposits where they 

 come out from under the Eocene by original relationship of 

 deposit. In this respect the Boulder-clay fully resembles the 

 Loess, although in the eastern counties of England there 

 were at the time of its deposit no eminences that, rising above 

 the sea, escaped its envelope, as did the higher ridges of the 

 Ardennes. 



On the other hand, we have, in a section given by Sir Chas. 

 Lyell in his paper on Belgium before referred to, a parallel, in the 

 case of the Campinian sands, to the erosive action exerted by the 

 sea of the lower Drift. The section is that at Dieghem, seven 

 miles north-east of Brussels. Sir Charles describes sands at that 



* The postpliocene gravels of the Thames valley have, however, been 

 powerfully disturbed by the raovements subsequent to those of the circular 

 character. 



