Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/331

 down the valley of the Avon, at a height of from 20 to 50 feet above its present course, and that the gravel previously brought into the district by marine currents was remodified by the river- stream, and mixed up with the remains of the mammalia and mollusca which tenanted its banks or its waters" (see Brit. Assoc. Reports, vol. vi. Sections, p. 64). I submit that the above view may be extended to other portions of the same area. Thus there appears to be evidence of: —

(1) A former time when the main valleys of the Avon and Severn existed pretty much in the state in which we now find them.

(2) A period when the greater portion of them were filled up, to a considerable extent, with the drifts of the upper and lower series, during the latter part of which, perhaps when the land was emerging, an arm of the sea occupied the lower portions of the Avon and Severn valleys, reaching probably to a height of from 200 to 300 feet, or thereabouts, above the present sea-level, at which time, we may suppose, with Sir R. Murchison, that the mammalian remains found near Worcester were washed into the ancient estuary from the neighbouring land-surfaces by sudden and local floods, and imbedded along with marine shells in the beds of sand and gravel, the negative evidence of the absence of freshwater shells, coupled with the occurrence of marine shells, preventing our having recourse to fluviatile agency for their transport. At the same time probably, the local drift at the base of Bredon Hill, containing marine shells and remains of mammalia, was deposited.

Towards the close of this period, and probably after the state of things just described had passed away, the sea having receded to about its present position by a further elevation of the land, and the action of the retiring waters having perhaps scooped out channels in the marine deposits in parts of the valleys, leaving eroded surfaces of clay and marl, upon which is found so large a percentage of the mammalian remains, the ancient river Avon brought down detritus derived from the adjacent beds of marine gravel, redepositing it in stratified beds along with land and freshwater shells over the surface of the clay; whilst the river Severn, in its turn, may have borne the detrital matter brought down from the marine deposits of the valley, along its comparatively straight course, towards the sea. This process of removal and redeposition may be supposed to have gone on until the final excavation of the beds of the rivers through the basement clay and marl to depths of about 30 and 50 feet respectively, as evidenced by the banks overhanging the present rivers in various localities, had reduced them to their present levels. Finally, the rivers having attained a state of equilibrium, they deposited the silt and vegetable matter brought down in times of flood, and spread them out in beds of modern alluvium. The foregoing outline of the probable succession of events belonging to the later geological history of the district is, it must be confessed, manifestly imperfect, and inadequate to explain satisfactorily many of the facts, partly owing to the necessarily meagre amount of positive evidence attainable, and partly depend-