268 
ME. PRESTWICK! ON THE GEOLOGY OF THE DEPOSITS 
pebbles*. At none of these places is there any admixture of old-rock pebbles. These 
latter all come into the valley of the Seine through its tributary valley of the Yonne, 
which, with that of the Cure, originate in the Morvan — a district consisting of granitic, 
porphyritic, and slate rocks, forming ranges of hills from 800 to 1200 feet high. 
The valley of the Aube, which joins that of the Seine between Nogent and Troyes, 
contains only oolitic and cretaceous debris ; so also, judging from the incidental notices 
of M. Coknuel, the upper parts of the valley of the Marne and its tributaries. These 
valleys traverse Cretaceous and Jurassic formations only (see Map, Plate IV.). 
Speaking of the gravel of the valley of the Oise, M. d’Archiac remarks that it “is 
composed of the debris of tertiary, secondary, and transition rocks, always rolled, and 
that the characters of the deposit vary according to the region from which its con- 
stituent elements have been brought, and consequently according to the valleys where 
these are found” f. The slate rocks of the Ardennes, from which the Oise flows, form a 
range of hills on the frontiers of Belgium, from 1400 to 1600 feet high. 
The next feature we have to notice in the high-level valley-gravels is the presence of 
large boulders, and the irregularity, confusion, and general want of stratification of the 
beds, which are, further, frequently contorted. 
In the valley of the Waveney there are no hard rocks to furnish boulders; the few 
therefore that are found are derived from the Boulder Clay ; but very large masses o£ 
flint with sharp and intact angles are common. In the valley of the Lark the features 
are precisely analogous. At Flempton we found, mixed up in the flint gravel, large 
blocks of half a ton weight of basalt and hard sandstones derived from the Boulder Clay. 
At Biddenham in the valley of the Ouse the lower part of the gravel is full of small 
blocks of oolitic limestones and sandstones very little worn, and there are none of a 
large size. In the valley of the Thames, boulders of large size are rare ; I have not met 
with ten in the course of as many years. 
In the valley of the Aire, M. Sauvage and Buvignier remark that the gravel capping 
the hills has an irregular surface and is waved (ondule). In the valleys of the Seine 
and Aube, M. Leymerie describes the base of the gravel capping the hills at Frenoy as 
irregular, and at Troyes as containing blocks and angular pieces of shelly neocomian 
strata, together with a few unworn flints. At Brienne the gravel also wants regularity. 
In the valley of the Oise at Guise, M. d’Archiac states that this gravel contains some 
fragments of quartz “ the size of the fist,” and that it is “ without distinct stratifica- 
tion” In the valley of the Seine, M. Charles d’Orbigny, in speaking of the lower 
bed of the gravel at Joinville, remarks that it forms “ a tumultuous deposit, at the base 
of which are found large erratic blocks §. One mass of tertiary sandstone (B, fig. 12) 
measured by us was 8^ feet long by 8 feet 4 inches thick, and was on the top of 
the light-coloured lower gravel (diluvium gris), or rather at the base of the red gravel 
(diluvium rouge). 
* Leymerie, op. cit. p. 92. 
f Mem. de la Soc. Geol. de France, vol. v. p. 188 ; and Graves, op. cit. pp. 535, 542. 
$ Ibid. p. 193. § Op. cit. p. 68. 
