148 A. J. Jukes- Browne — Inter glacial Land-surfaces. 



revives the question of Man's first arrival in Britain, carrying this 

 back to Inter-Glacial, though not necessarily to Pre-Glacial times. 



Dr. Hicks's inferences are, however, disputed by Prof. Hughes, 

 whose objections may be summed up as consisting of two assertions 

 — (1) that the deposits concealing the north-west mouth of the 

 cave are not true Boulder-clays, but consist of rainwash and 

 re-sorted Drift ; (2) that if they did belong to what he calls the 

 Clwydian Drift, they would still be Post-Glacial, and not Glacial. 



Upon the first point it would appear that the majority of those who 

 saw the excavation are against Prof. Hughes, and as fresh openings 

 are to be made next June, we may hope that geologists who are 

 acquainted with the Glacial beds of Cheshire and Lancashire will 

 visit the place, and give us an authoritative opinion. In the mean 

 time I may draw attention to the regularly stratified succession of 

 sands and Boulder-clays in Dr. Hicks's section (see Geological 

 Magazine, December, 1886, p. 569) ; this is not the kind of 

 structure which rainwash deposits usually exhibit. 



Prof. Hughes's second objection is simply an unwarranted assump- 

 tion ; his only grounds for the statement that the so-called Clwydian 

 Drift is Post-Glacial appear to be that it is of marine origin, and 

 was formed during " the submergence which followed the extreme 

 glaciation." Prof. Hughes may choose to assume that Post-Glacial 

 time commenced with this submergence ; but this is not the view 

 which is usually held, and students of Pleistocene geology will 

 naturally call upon him to define what he means by the terms 

 Glacial and Post-Glacial. The latest authorities are agreed in 

 correlating the Boulder-clays and gravels of the Vale of Clwyd with 

 the similar deposits which spread over such large areas in Cheshire 

 and Lancashire, and he must be a bold man who would exclude 

 these from the category of Glacial deposits. 



It is true that the late Mr. S. V. Wood, Jun., made a similar 

 assumption with regard to the Drifts of Lincolnshire, speaking of a 

 major and a minor glaciation, and referring the product of the latter 

 (Hessle Beds) to the Post-Glacial era, because they contained 

 Cyrena fluminalis, and were in his opinion contemporaneous with 

 certain river-gravels which are usually called Post-Glacial. I have 

 elsewhere shown, however, that the Hessle beds are so intimately 

 associated with the underlying Purple clay that they cannot possibly 

 be dissociated from it ; and that as both were evidently formed under 

 glacial conditions, it would be both confusing and illogical to call 

 any part of the series Post-Glacial. 



The fact is, as Prof. Boyd Dawkins has pointed out, the so-called 

 Glacial period was only an episode in Pleistocene time ; the length 

 of this episode was necessarily different in different parallels of 

 latitude, and consequently the term Post-Glacial can only have 

 a local significance. Deposits which ai'e evidently the products of 

 ice-action must be called Glacial, and Post-Glacial deposits could 

 not be formed at any given place until glacial conditions had ceased ; 

 hence it is probable that the Post-Glacial deposits of southern 

 England are of earlier date than those of northern England, while 

 in France the term Post-Glacial ceases to have any value at all. 



