BOULDER-CLAY IN LINCOLNSHIRE. 413 
The point in dispute might at first sight appear to be a mere 
matter of nomenclature; but the question really involved is whether 
the Hessle beds are synchronous with the March gravels and with 
the brickearths of the Thames Valley. Believing, as Mr. Wood 
does, that the Hessle beds are contemporaneous with deposits in the. 
south of England “‘ which for more than a quarter of a century we 
have been accustomed to call Postglacial,” it is not surprising to 
find him remarking that, had he not called the former beds Post- 
glacial, his contention of their synchronism with Postglacial deposits 
would haye produced great confusion. All this seems sufficiently 
reasonable and logical, granting, of course, that the premises are 
correct ; but if these are shown to be unreliable, the whole argument 
necessarily becomes invalidated. 
If we examine the history of the term “ Postglacial,” we shall 
find that it was adopted by Prof. Prestwich in 1864 to designate 
the period during which the English river-gravels were deposited, 
because even the oldest of these could be shown to be of later date 
than the Great Chalky Boulder-clay of East Angla, which was then 
regarded as the only clay formation of the Glacial Period. 
When, however, it was subsequently discovered that there were 
newer Boulder-clays than the so-called Upper Glacial, it became 
clear that some of the river-gravels might belong to the period 
during which in the more northern parts of England these later 
clays were being formed. Mr. Searles Wood saw reason to think 
this was the case; and he says it was expressly with the object of 
preventing confusion that he called the Hessle beds Postglacial, 
because they were, in his opinion, synchronous with the Cyrena- 
brickearths. 
Finding also that the Hessle Clay did not present the same cha- 
racters as the older Boulder-clays, that its mode of occurrence was 
different, and that it was separated from the older beds by a long in- 
terval of time (during which the present valley-system of Lincolnshire 
was carved out), he thought these were sufficient reasons for regard- 
ing the Great Chalky Clay as the last term of the Glacial series, and 
that the extensive denudation which followed the elevation of these 
Glacial beds into dry land might be taken as ushering in the Post- 
glacial Period. 
He considered that this conclusion was supported by the character 
of the Molluscan fauna of the Hessle Sands ; so that in 1872 he thus 
stated the case* :—‘‘ The Hessle beds do not, I contend, belong to the 
Glacial period at all. They followed the re-occupation of the terres- 
trial surface by the Great Mammalia, of the rivers by Cyrena 
Jluminalis, and of the seas by a molluscan assemblage, not merely 
all of living species, but one that differs in but a slight degree from 
that inhabiting the English coast near at hand.” 
Such are Mr. 8. Wood’s grounds of belief ; and since the division 
between the two periods, wherever it is drawn, must, to some ex- 
tent, be an arbitrary line, there would not be any great objection to 
this classification, provided that the sequence and parallelism in- 
* Geol. Mag. vol. ix. p. 174, 
