CONTAINING FLINT IMPLEMENTS, AND ON THE LOESS. 
277 
escaped through the soft and pasty silt, leavened, as it were, the mass, and produced 
these innumerable tubular cavities. 
Sometimes the Loess puts on a local character, derived from either adjacent chalk, 
sand, or clay beds. It then becomes so modified as to render its true character not 
easily distinguishable. In some cases it becomes very argillaceous, in others very sandy 
or very chalky. Occasionally it is so full of angular rock- or flint-fragments as to pass 
into an angular gravel. It is the presence of a local bed of this nature, made up in part 
of the angular fragments so peculiar to the Loess, and partly from the subangular gravel 
taken up from the underlying white gravel (Diluvium gris), and generally deeply coloured, 
which has given rise, in a number of cases, to the Diluvium rouge (part) of the French 
geologists, as exhibited in the sections at Charonne, Gentilly and Joinville, as well as at 
Abbeville and Amiens. Therefore, so far from being a separate deposit, this bed at these 
places is, I consider, merely an accident of the Loess, which again is merely a condition 
of a river-deposit of the period of the valley-gravels ; so that, instead of the four separate 
deposits of ‘ Loess,’ ‘ Diluvium rouge,’ 4 Sable lacustre,’ and ‘ Diluvium gris,’ into which 
some able French geologists would divide the deposits at Gentilly, Joinville, St. 
Acheul, &c. *, I would divide them, on lithological characters alone, into two groups — 
the Loess and the Valley -gravels; whilst so far as age is concerned I should consider 
them as one, representing phases of like causes under different conditions. 
§ 5. ORGANIC REMAINS OF THE YALLEY-GRAYELS. 
As it is very desirable to determine whether any changes in the fauna occurred during 
the period which elapsed between our earliest fossiliferous high-level valley-gravels and 
the latest low-level gravels, I have attempted to form separate lists of the organic re- 
mains of each series. I feel, however, that we are not yet in a position to do so with cer- 
tainty or completeness. The difficulties in the way are, 1st, the uncertainty as to which 
series the beds may in some cases belong to ; 2nd, the frequent absence of record as to the 
level at which the organic remains have been found ; 3rd, the incompleteness of the search. 
I therefore submit these results merely as an approximation and a commencement. 
I am indebted to Dr. Falconer and M. Lartet for much valuable information respecting 
the mammalian remains, and to Mr. Gwyn Jeffreys for the correction of my former 
lists of the Mollusca, and for his kind assistance in determining additional species. 
As a term of comparison for the Mollusca, I have taken the group of land- and 
freshwater shells now inhabiting the districts^ where the fossil species are found, 
adopting, generally, Mr. Gwyn Jeffreys’s nomenclature and distribution for England, 
and taking for their range in France M. Picard’s “ shells of the department of the 
Somme M. Bouchard-Chanteroux for those of the “Pas de Calais,” and M. Baudon§ 
* Bull, de la Soc. Geol. de France, 2 e ser. vol. xii. pp. 1277, 1297, 1298 ; vo! xvii. pp. 18, 19, 67-78, 103. 
(With reference to M. Hubert’s observations, 2 e ser. vol. xvii. p. 18, see his “ rectification,” vol. xii. p. 255.) It 
was not until towards the end of 1859 that this able geologist expressed belief in the discoveries at St. Acheul. 
t Forbes and Hanley’s * British Mollusca,’ and Mr. Gwyn Jeefreys’s ‘ British Conchology,’ vol. i. 
+ Journ. de la Soc. Linneenne du Nord de la France, vol. i. p. 149. § Soc. Acad, de l’Oise, 1855. 
