910 PROFESSOR J. PRESTWICK ON THE EVIDENCES OF A SUBMERGENCE 
common in the chalk hills of Kent, consisting of trails of ochreous gravel. These are 
usually attributed to the action of former streams, but they seem to me to be more 
intimately connected with the rubble-drift, into the main body of which these gravel- 
streams debouche in the plains below.* Such, for instance, as in the case of the 
narrow stream of unstratified ochreous gravel from 3 to 10 feet in thickness, which 
descends the dry chalk valley from near Pihen to Hames, where it enters the broad 
alluvial plain near Guines. Midway in this stream of gravel M. Sauvage found a jaw 
of Rhinoceros tichorhinus.^ 
Fig. 3 .—Section from Sangatte Cliff to above La Queenvaclierie. 
jv:w s.E. 
The relation of these streams of gravel to the head at Sangatte is similar to that 
which exists between the head (Elephant Bed) at Brighton and the drift in the bed of 
the valleys on the coast of Bottingdean and other places thence to Eastbourne.;}; They 
all consist of debris from the surrounding hills, except that in the one case only a 
trail has been left, whilst in the head it has accumulated en masse. 
There is a small counterpart of the chalk-rubble on the Wissant side of Blanc Nez; 
and at a short distance out of Wissant on the road to Tardinghen is a hillock of 
gravel, containing a remarkably large proportion of chert fragments of the Lower 
Greensand, referable probably to the Bubble-drift. 
Thence to Boulogne there is little to notice, the encroachment of the sea ha^fing 
removed all the later coast deposits, only leaving here and there slight traces of 
angular rubble. To this also belongs a pocket of drift with remains of the Mammoth 
exposed in carrying the railway through the Kimmeridge clay on the high slopes 
between the old town of Boulogne and the coast. 
Abbeville .—The sections here are of much interest, as they show the relation of the 
Bubble-drift to the fluviatile deposits of the old river, and likewise to the Baised 
Beaches. The marine or estuarine bed at Menchecourt is 24 feet above the sea-level, 
which, allowing for its distance inland, corresponds wfith that of the Baised Beaches of 
the Channel. It is here, however, overlaid by the old river beds -with fluviatile shells 
* In some instances streams may have preceiled tliese later gravel trails, 
t The specimen is in the Boulogne Museum. 
J See section in ‘ Quart. Journ. Geol. Soc., vol. 48, Plate 7, fig. I. 
