H. H. Howorth—A Great Post- Glacial Flood. 419 
It is surely a most complete proof of the chain of inference we have 
moulded, connecting the marine gravels of Moel Tryfaen with the 
ossiferous beds, that the marine shells in these Hessle beds, which 
are dovetailed into the ossiferous and Cyrena-bearing gravels, should 
be of the same types as those found at Moel Tryfaen and Maccles- 
field, and like them contain no species “but such as now live in 
the sea surrounding the British Isles, or in that immediately north 
of the Shetlands.” And it is no small support of such an induction to 
find Mr. Searles V. Wood saying expressly that ‘the Hessle sand and 
gravel is the equivalent of the Middle sands of Lancashire” (Journ. 
Geol. Soc. vol. xxxvi. p. 525). On this point we may refer to 
another veteran writer on these beds. Joshua Trimmer, speaking 
of the Boulder-clay and the associated gravels and sands, says: 
“ Notwithstanding the distance which separates the Till of the coast 
of Norfolk from that of North Wales and Ireland, he recognized a 
common character pervading the whole, which he attributed to their 
having had a common origin, being derived from the north, and he 
considered that the cause of the deposit of this Boulder-clay covered 
with sands, loam, etc., of a yellow colour, seemed to have acted but 
once, the same appearances not recurring” (J.G. 8. vol. i. p. 219). 
Tf, instead of turning eastwards, we travel towards the south, we 
shall find the same continuity established there. It has ever been a 
mystery that the Thames Valley should be deemed a complete 
barrier between Glacial and non-Glacial beds. Neither its physical 
configuration nor its other features will enable us to conceive how it 
should have been so. We have treated it as such in these papers. 
merely for convenience, but we hold to no such position as a fact. 
The Boulder-clay no doubt thins out as we go south and disappears ; 
_ but the Boulder-clay is largely a characteristic of maritime districts, 
and does not occur in vast typically glaciated areas such as many 
parts of Northern Sweden. If we put it aside as a local phenomena, 
and if we consider that the grooved surfaces, etc., which are so 
characteristic of the crystalline hard rocks in the north could not 
exist in the soft beds of the south except under very favourable con- 
ditions, we shall cease to wonder that there are so few traces of actual 
Glacial action south of the Thames. This is parenthetical only how- 
ever. What we are urging now is that the barren and ossiferous 
gravels of Central England which are marked by triturated pebbles 
pass more or less insensibly by a gradual introduction of subangular 
and angular pebbles into the Angular Drift of the Hnglish Channel, 
and thus into the diluvium of the French writers. ‘This has been 
shown by many observers. In Cornwall and Devon and in Kent the 
transition may be studied most graphically. 
The lessons to be learnt from these southern and transition gravels 
have been at least outlined by Mr. Belt. ‘The facts to be ex- 
plained,” he says, “not only in Devon and Cornwall, but over the 
whole of the South of England, are—1. Gravels containing travelled 
boulders on the sides and tops of the hills up to about 1200 feet 
above the sea; 2. Denudation of the surface gravels in an inter- 
vening tract between the Upland and Lowland deposits; 3. In the 
