256 
ME. PEESTWICH ON THE GEOLOGY OF THE DEPOSITS 
absence of the marine pliocene and post-pliocene beds in the North of France, we 
there obtain clearer evidence relating to the valley-gravels, as they are free from rock- 
fragments and boulders foreign to their own origin and area. From causes to which 
we shall presently allude, the whole class of these phenomena is also more marked 
and on a larger scale in France than in England, and has attracted more attention 
and been more fully investigated. It is sometimes not easy to determine the high- 
level gravels in our valleys, whereas in France they are generally on a scale of height 
and extent which prevents any doubtful interpretation of their relative position. 
Valley of the Somme. — M. Buteux * gives a number of localities at which the beds 
he terms Diluvium occur in the valley of the Somme, between Amiens and St. Quentin, 
but without going into structural details and levels. On my first visit to St. Acheul and 
St. Boch I suggested the possibility of the beds at the former place f being a stage 
older than the latter. The distance between them being 1^ mile, it seemed quite possible 
that the difference of level might have arisen from other causes than a further excava- 
tion of the valley subsequent to the deposition of the St. Acheul beds, and anterior to 
that of the St. Boch beds, but the difficulty of proof was considerable ; the existence of 
faults, the slope of the ground, or an unequal extent of elevation might have been the 
cause of the difference. The point being one of importance in its bearing on the ques- 
tion of the age and antiquity of the St. Acheul beds J, I reserved my opinion in the hope 
of finding better evidence elsewhere in this valley. 
At a distance of from one to two miles N.W. from Amiens, and parallel with the river, 
is a series of large pits extending past Mon tiers along the road to Abbeville. The gravel 
is on the same level and of the same character as that of St. Boch. Few mammalian 
remains, and no shells or flint implements, had been found there up to the period of my 
first visit in 1859. As at St. Boch, the gravel abuts against a low chalk hill, and no 
fossiliferous gravel had been met with on the hill above. The railway runs just at the 
back of the pits, and at a height of some 30 feet above them. In the spring of 1860 I 
found a pit just opened immediately above the slope of chalk through which the line 
passed, and in such a position that the gravel could be wheeled on a level from this 
new pit into the railway trucks in the cutting. In position and level this last deposit is 
related to the beds of St. Acheul as the beds in the old pits are to that of St. Boch ; 
but here the two beds were in close and determinable proximity. The section from 
one to the other is fortunately perfectly clear, and I could detect no fault in the 
separating chalk ledge cut through by the railway. 
* Esquisse Geologique du departement de la Somme, Paris, 1849, and two supplements ; and 1862 ; also a 
paper by the same author in Mem. de la Soc. d’Emul. d’ Abbeville for 1857, p. 561. 
f Phil. Trans. 1860, p. 303. 
t I have since been enabled to trace, by means of some trial pits near the Amiens railway station, the low- 
level gravel with remains of Rhinoceros tichorhinus close up to the base of the hill on the top of which the 
St. Acheul gravels extend, forming a section therefore very analogous to that at Montiers, and establishing 
directly the relation of the St. Acheul beds to the lower-level gravels, which continue uninterruptedly from the 
railway station to St. Eoch. — Feb. 1864. 
