temporaneous current action. The way in which the Boulder 

 Clay runs down into the valley about Newport and Wenden 

 shows that this was a pre-existent hollow ; it would therefore 

 form a narrow strait at the first incidence of the Boulder Clay 

 (always supposing this to be a marine deposit) ; consequently it 

 is only likely that a current would set through the gap and give 

 rise to patches of sand and gravel, interstratifying them with 

 the lower portions of the Boulder Clay itself. 



I agree therefore with Mr Penning, that there is no evidence 

 for the existence of Middle Glacial beds in the Cambridge 

 valley, and that the earliest glacial deposit is the Upper 

 Boulder Clay. Mr Searles Wood considers this as the upper- 

 most and latest of the glacial series, and he proposes to class as 

 Fost-glacial all beds which can be proved to lie unconforraably 

 on this clay. It seems to me, however, that it is more reason- 

 able to consider the great chalky Boulder Clay as accumulated 

 during the most intense period of glacial cold, and I do not see 

 why other beds should be excluded from the glacial series 

 simply because they happen to lie above this particular clay. 



Supposing, with Mr S. V. Wood, that the glacial beds are of 

 marine origin, and that the Boulder Clay was deposited during 

 the great submergence, surely marine glacial gravels are just as 

 likely to have been formed during the elevation as during the 

 depression of the shore line ; it is indeed a well known fact that 

 there are large spreads of gravel above the Boulder Clay which 

 have none of the appearance of ordinary terrestrial gravels, 

 and which have been termed " Plateaux Gravels " by Mr Wood. 



I believe them to be in great part the Upper Erratics of 

 Mr Trimmer. Mr Searles Wood however appears to be only 

 acquainted with these Plateaux Gravels in Norfolk ; he speaks 

 of them in the following terms* : "This gravel is everywhere 

 unfossiliferous and is composed almost entirely of flints. It 

 is difficult in some cases to form an opinion whether it is of 

 glacial or post-glacial age. Most of that shown in sections is 

 doubtless post-glacial, but with respect to that which caps 

 Mousehold Heath it seems the same as the gravel which has 

 an extensive spread in West Norfolk, since, like it, the gravels 



1 Preface to Monograph on Crag Mollusca (Palaeont. Society). 



