/S. V. Wood, Jan. — Sequence of Glacial Beds. 1 7 



mucli of the denuded material, as Mr. De Ranee observes, liaving 

 found its way to the sea. That such alluvial deposits as those 

 named above have been formed since the Glacial Period, is evident 

 by the way in which they lap round and cover up ice-smoothed and 

 ice-scratched bosses of rock ; and if, in this comparatively short time, 

 such denudation has taken place, what amount of material may not 

 have been removed since Permian times ? 



V. — Observations on the Sequence of the Glacial Beds. 

 By S. V. Wood, Jiin., F.G.S. 



THE Article in this Magazine by Prof. Ilarkness, " On the Middle 

 Pleistocene Deposits of Britain"^ will, I trust, call the attention 

 of geologists more prominently to the fact that a break occurred in 

 the Glacial period, wherein the formation of Boulder-clay was 

 arrested for a considerable interval, and an extensive formation of 

 sands and gravels spread out, accompanied, apparently, by some 

 amelioration of the temperature of the sea. Nevertheless, there are 

 several things pressed by Prof. Harkness into his case as to which, a 

 word of caution, and even of dissent, seems necessary. 



I would preface these remarks by venturing to demur to any 

 attempt to determine the succession of the Glacial and Post-glacial 

 marine series by the evidence of organic remains alone, and to urge 

 that this kind of evidence, unless kept strictly subordinate to that 

 afforded by the physical relations of the beds, as well as by mapping, 

 or other close method of pursuing them, is more likely to mislead 

 than assist, in consequence of almost all the shells belonging to 

 species now existing. There are, however, two marked facts con- 

 nected with this kind of evidence which I think may be relied upon. 

 These are : 1st, that the presence of Tellina Balthica (solidula) is a 

 test that the bed yielding it belongs to the Glacial or Post-glacial 

 formations, and not to any of the Crag series f and 2ndly, that the 

 absence of Tellina ohliqua affords a presumption^ that the bed — at 

 least any English bed — from which it is absent is of Post-glacial age, 

 meaning by such term that it belongs to the period during which 

 the land was rising from the great Glacial submergence, or to the 

 time which followed emergence. With these two exceptions, I would 

 urge — and as much in depreciation of my own inferences as those 

 of others — that any conclusions sought to be deduced from a list 

 of MoUusca should be received with large savings on various 

 accounts. 



With that premise, I venture to doubt whether Prof. Harkness 

 has not included in his extensive sweep of identification with the 

 Wexford Gravels some beds that can hardly by any possibility be 

 identical. 



How far the identity he seeks to establish between the gravels of 



1 Vol. vi., p. 543. 



^ As this shell has so long, but erroneously, been included in lists of Crag shells, it 

 may be useful if I add that it is not given as a shell of the Belgian Crag by M. Nyst. 



2 Subject, however, to the doubt expressed further on in this paper, 



VOL. VII. — NO. LXVII. 2 



