to floods extending to a height of at least 80 feet above the level of the rivers, we may well hesitate before we give in our adhesion to such views. In the first place, it is, to say the least of it, unphilosophical to rely too much on a single example, such as that of the valley of the Somme; and to account for its phenomena by causes which are evidently incapable of producing the effects observable in other localities, as, for instance, at Southampton, close to the sea, and 160 feet above its level. But what shall we say to floods raising the levels of rivers upwards of 80 feet, yet having no erosive power, and the waters of which, regardless of the laws of gravity, tranquilly deposited their solid contents evenly over the slopes, or often in the greatest thickness on their higher part, and in some cases on almost isolated hills, instead of principally on the bottom of the river-valley? Whence all the materials for the gravels are to be derived, how they are to be reduced to a subangular condition by water-wear, especially in the case of the flint implements occurring in the gravels, are points on which further information will have to be supplied, before any such views can be seriously entertained.
I have up to this point almost left out of view any distinctive differences between the deposits at a high level and those at a low level in the river-valleys. That such, however, exist has been pointed out by Sir Joseph Prestwich;[1] and judging from the northern range of the group of shells found in the high-level beds, the absence of southern species, the character of the mammalian and vegetable remains, the transport of large blocks such as could only be effected by ice and the other physical features of the case, he is inclined to assign a winter temperature to the period of their deposit from 19° to 29° Fahr. below that which now obtains in these regions. From a consideration of the features of the low-level deposits he considers that at the time of their deposit, the climate was rather less severe, by about 5°. The presence of the mammoth and woolly-haired rhinoceros, animals specially adapted for cold climates; of the musk-ox, the reindeer, the lemming, and marmot, corroborates the same view; while the hippopotamus, which seems characteristic of the low-level deposits, is suggestive of a somewhat warmer climate. Like the mammoth and rhinoceros, its structure may, however, have been somewhat modified, so as to enable it to occupy colder regions than at present, or it may have been merely a summer visitor ranging northwards before the
- ↑ Phil. Trans., 1864, p. 278, &c.
