Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/589

Rh those beds were deposited by the agency of rivers involves so many difficulties and objections, that it can hardly be accepted without much further consideration than the subject has received, much as it has been discussed. Indeed, unless we are prepared to admit that all the Quaternary gravels were brought to their present places of deposit by the agency of rivers (which is evidently impossible), it is unreasonable to attribute to that agency any particular portion of those gravels merely because they happen to contain implements.

Considerable differences of opinion exist between French and English geologists as to the causes which led to the accumulation and distribution of those superficial drifts in the south-east of England and north of France of which the flint-implement-bearing beds form part: while the French geologists unanimously attribute them to some kind of cataclysmal or diluvial action (although they differ among themselves as to its particular character), the English geologists are nearly unanimous in ascribing them to the action of existing rivers, or at least of rivers which then ran in the same direction as they now do, and drained the same areas. The present is not a convenient occasion for considering this subject at any length. I propose only to show how inadequate, as it seems to me, is the theory of fluviatile transport to explain the condition of the deposits before referred to and of others of a like character.

The opinion of English writers cannot be better stated than in the words of Mr. Prestwich, from the able and exhaustive memoir upon the flint-implement deposits read by him before the Royal Society in 1862. He says, "that certain beds of gravel, at various levels, follow the course of the present valleys, and have a direction of transport coincident with that of the present rivers, and that the extent and situation of some of these beds so much above existing valleys and river-channels, combined with their organic remains, point to a former condition of things when such levels constituted the lowest ground over which the waters passed;" further, "that the size and quantity of débris afford evidence of great transporting power; while the presence of fine silt, with land shells, covering all the different gravel-beds, and running up the combes and capping the summit of some of the adjacent hills to far above the level of the highest of these beds, points to floods of extraordinary magnitude;" that "these conditions, taken as a whole, are compatible only with the action of rivers flowing in the direction of the present rivers, and in operation before the existing valleys were excavated through the higher plains, of power and volume far greater than the present rivers, and dependent upon climatal causes distinct from those now prevailing in these latitudes"; and he adds that "such a result might formerly have been obtained, 1st, by a direct increase in the rainfall; 2ndly, by the accumulation and rapid melting of the winter snow, or by the two causes combined; and 3rdly, by the fall of rain in the spring while the ground was in a frozen state."

Mr. Prestwich's opinions have been acquiesced in both by Sir Charles Lyell and Sir John Lubbock. The latter, in his preface to the recent English edition of Sven Nilsson's 'Primitive Inhabitants of