In proof of the sea having advanced upon the land, there are vestiges of submerged forests (the stumps of the trees standing erect where they grew, at or a little above the present lowest ebb) existing at different places on the eastern coast, both of England and Scotland, and these vestiges standing upon a former carse or alluvium of the rivers, are visible in the same firths with the upper level of carse, of course generally more to seaward than these higher carses, as deposition of rivers occurs at what may be termed deposition point, that is where the rivers, from the stemming of the sea-water, begin to widen—where the firths commence; and the slowness of the motion of the water gives time for the subsidence of the floated mud. By reason of the flux and reflux of the tide into the mouths of rivers, this deposition takes place only at or near high water, that is, when the strength of the inward tide-flux ceases, and before that of the reflux begins. It is {292} most abundant at the windward shore, or where there is least surf, and among the tall gramina and other vegetation where there is least undulation and current; the deposition which occurs at this time, some distance below high water level, is floated away by the current of the following flux and reflux, unless some object afford a nucleus of formation. Hence deltas or carses usually form near the shore of firths, generally soon rise to high-water level, and have often steep, or even abrupt, banks, collecting at one place, and giving way before the waves and undermining current at another. There is a deposition of another kind than river diluvium, which also takes place at the bottom, or further end, of bays and firths, and is sometimes mixed with the preceding: This consists, as mentioned above, of the abrasion of the rocks, or shores of the bay and neighbouring coast, and also of molluscous exuviæ, borne along by the motion of the waters; but this is generally rather an accumulation than a deposition, occurring in greatest quantity where a heavy swell rolls dead in.