BOULDER-CLAY IN LINCOLNSHIRE. 415 
fossil in question—a fallacy which Mr. H. B. Woodward has exposed 
in his recent address to the Norwich Geological Society *. 
Mr. Wood’s dependence on the testimony afforded by the presence 
of Cyrena fluminalis has led him into another error ; for he groups 
together the March and Barnwell gravels, which are now found to 
be entirely disconnected. The danger of trusting to so small an 
amount of paleontological evidence is thus illustrated. Deposits 
which contain similar fossil assemblages may be compared ; but de- 
posits which only happen to contain one fossil in common are 
palzontologically incomparable. 
The testimony in favour of the Postglacial correlations is not 
even of so plausible a nature as that for the Preglacial classification ; 
for Cyrena fluminalis is known to have existed previously during 
the later Crag-formations ; 1t was probably only banished from Eng- 
land during the coldest times of the Glacial Period, and returned 
whenever the conditions permitted its existence ; it is by no means 
of universal occurrence in the older river-gravels themselves, its dis- 
tribution being apparently dependent upon climatic conditions and 
other circumstances ; so that it cannot be used even here as an in- 
fallible criterion of age: ¢. g. the Barnwell gravels contain it in 
abundance; but it has not yet been found in the freshwater portion 
of the older series above mentioned. 
I will now examine on separate and independent grounds the 
probability of any of the deposits indicated by Mr. 8. Wood being 
contemporaneous with the Hessle Sands. 
(1) The Hunstanton Gravel. The marine character of this deposit, 
together with its position above the level of the Fenland, lends some 
colour to the supposition of its synchronism with the Hessle beds. 
Mr. Wood thus speaks of it +:—‘‘ The Hunstanton gravel resembles in 
its paleontological aspects the Kelsea Hill bed in consisting entirely 
of living species, and none but those inhabiting British Seas have 
yet been obtained by us from it. Itis not, however, overlain by any 
thing answering to the Hessle Clay... . neither does the Cyrena occur 
in it.” This raised beach has not, indeed, been fully investigated ; and 
its relation to the other drift beds in the neighbourhood is at present 
unknown. A careful examination wouid probably lead to some inter- 
esting results; for a little south of the point where the Red Chalk 
rises to the top of the cliff at Hunstanton, a stiff reddish-brown clay 
takes the ground, presenting a pebbly base and lying in hollows 
eroded out of the Carstone ; it deepens southwards towards the sta- 
tion and becomes more purple in colour. I hesitate even to hazard 
the suggestion that this may be a form of the Hessle Clay, as the 
possibility has only lately occurred to me, and my visit to Hunstan- 
ton was anterior to my acquaintance with the latter clay. 
(2) The gravels on the North Edge of the Fen. I have already 
stated the reasons which induce me to regard these as probably of 
later date than the Hessle Clay (see p. 414). I admit that, where 
* Proc. Norw. Geol. Soc. vol. i. p. 50. 
+ Introduction to Supplement of ‘ Crag Mollusca’ (Pal. Soc.), p. xxviii, 
Q. J. G. 8. No. 139. 26 
