CONTAINING FLINT IMPLEMENTS, AND ON THE LOESS. 
267 
certain proportion of the chalk-flints found in the gravels of both valleys, can be traced 
to the adjacent Boulder Clay. 
I have noticed the same facts in almost all the river-valleys of the South-east of 
England where the valley passes through belts of different formations, as, for example, 
the occurrence of Wealden and Greensand debris on the chalk hills in the valley of the 
Medway, between Maidstone and Rochester ; and in the same manner the occurrence of 
Purbeck and Greensand debris on terraces in the valley of the Wiley between Wilton 
and Salisbury. Traces of Greensand and Oolitic debris are to be detected in the valley 
of the Thames, also mixed with debris of the Boulder Clay. 
With reference to the French area, the phenomena have been well studied by many 
French geologists*, to whose works, before cited, I beg leave to refer for fuller parti- 
culars than I can here introduce. I will say a few words, however, of the valleys of the 
Somme, the Oise, and the Seine, — more especially of such parts as I have myself visited. 
The Somme flows through a chalk district with a few tertiary outliers, while the 
tributary valley of the Arve penetrates to the main body of the tertiaries. At St. Acheul 
the quantity of sandstone blocks and pebbles, and of flint pebbles, derived from tertiary 
strata, is very considerable, and the presence of specimens of Nummularia laevigata and 
of the Venericardia planicosta shows the upland direction of their origin, as no beds 
containing these fossils exist below Amiens. In the several patches of high-level 
gravels (chiefly of subangular chalk-flints) between Amiens and Abbeville, tertiary debris 
continue to be found, and at Moulin Quignon sandstone-fragments of a large size are 
still numerous, although they are fewer and smaller than at St. Acheul f. 
The occurrence of rolled fragments and boulders of granite and other old rocks in the 
valley of the Seine at Paris, is a fact which has long been well known. The presence 
of similar materials of distant origin has also been proved to hold good in the higher- 
level gravels of Gentilly and Charonne. M. Duval described the section at the first- 
named place (which applies to the other), as consisting of sands passing downwards into 
a gravel composed of pebbles and fragments of cretaceous and tertiary rocks, together with 
others of porphyry, and “ a prodigious quantity of grains and pebbles of red granite ” J, 
some of which weighed from eleven to thirty-four pounds. Land and freshwater shells 
and small reptilian bones were common, with some bones of the large mammalia. 
The valley-gravels at Frenoy, Nogen t-sur-Seine, and Troyes consist chiefly of oolitic 
* The case is very clearly put by M. d’Aechiac in his admirable work the ‘ Histoire du Progres de la Geo- 
logic/ vol. ii. p. 139, where he observes, “ On reconnaitra que les materiaux des depots meubles sont distribues 
ou repartis exclusivement soit sur les flanes de certaines gibbosites principales et dans les vallees qui y pren- 
nent naissance, soit dans de larges depressions on bassins hydrographiques qui ne sont limites a leur pourtour 
par aucun relief bien prononce. Dans l’un ni dans l’autre cas il n’y a melange des materiaux transportes.” . . . 
. . . “ Cette distribution nous demontrera que l’orographie generate etait au commencement de la periode diluvienne 
a tres peu pres ce qu’elle est aujourd’hui, et nous reconnaitrons que les lignes de partage entre certains bassins 
hydrographiques et dont F elevation devait etre bien faible alors ont pu cependant restreindre les effets du phe- 
nomene erratique aux memes limites que les eaux qui se rendent actuellement dans chacun d’eux.” He excepts 
Great Britain and the North of Europe from the exhibition of these conditions. 
t See sect. figs. 3, 5, 6 in Phil. Trans, for 1860, pp. 287-290. + Op. at. p. 304. 
