267 
feature and geology, we extend the hypothesis to the whole 
north-west frontiers of the continent, and assume, that from 
the estuary of the Seine to the eastern shores of the Baltic, 
every internal feature of valley, dale, and ravine — in short, 
the entire intaglio of the surface — has been moulded by 
running waters, since the advent of the human race." 
Taking the section at St. Acheul, and commencing at the 
bottom, we have first of all the subangular gravel throughout 
which, though especially at the lower part, the flint imple- 
ments occur. A similar bed may be found here and there all 
along the valley of the Somme ; at St. Acheul it is about 
90 feet above the present river level ; at Moulin Quignon, 
near Abbeville, the same ; while at Picquigny and at Caesar's 
Camp, near Liercourt, we found it at a height of 150 feet. 
Though only occurring in places, this gravel is so similar in 
composition and contents, that we seem justified in assuming 
it to have been at one time continuous ; and we may almost 
take the section, as representing generally a section taken 
anywhere across the valley, only bearing in mind that 
through the action of subsequent causes, the gravel and the 
beds covering it have been in most cases removed. Nor is 
this a phenomenon peculiar to the Somme. During our last 
excursion we visited many gravel pits holding a similar 
relation to the Seine, while Mr. Prestwich in his recent com- 
munication to the Royal Sociefa^gtends the same statement 
to many other rivers in EnJgSipmd France, the greatest 
height of the gravel above tne present river level varying 
however in different cases. At St. Acheul and in several 
other places this bed of gravel, which for the future we will 
call the high level gravel, is separated from the low level gravel 
by a bare tract of the underlying rock. We do, however, 
sometimes find beds at intermediate levels, and must, 
therefore, consider the upper level and lower level gravels 
as the extremes of a continuous series, rather than as 
