An increase of deposition of alluvium, or prevention of decrease, may, in many cases, be accomplished by artificial means. The diminution of the carse of the Tay was in rapid progress about sixty years ago, the sea-bank being undermined by the waves of the basin, the clay tumbling down, becoming diffused in the water, and being carried out to sea, by every ebbing tide, purer water returning from the ocean the next tide-flow. This decrease was stopped by the adoption of stone embanking and dikes. A small extension of the carses of present high-water level, in the upper part of the firths of Tay and Forth, has lately been effected, by forming brushwood, stone and mud dikes, to promote the accumulation. {379} In doing this, the whole art consists in placing obstructions to the current and waves, so that whatever deposition takes place at high-water, or at the beginning of the flood-tide, when the water is nearly still, may not again be raised and carried off. Notwithstanding this accumulation, and also the prevention of further waste of the superior carse, the deepening of the Tay Firth, formerly carse, and of the gorge at Broughty Ferry, seems still in progress, and could not, without very considerable labour, be prevented. In the case, however, of the sea-basin of Montrose, a little labour, from the narrowness of the gorges, would put it in a condition to become gradually filled with mud. Not a great deal more expenditure than what has sufficed to erect the suspension-bridge over its largest outlet, would have entirely filled up this outlet, and the smaller outlet might have been also filled to within several feet of high-water, and made of sufficient breadth only, to emit the water of the river, which flows into the basin. The floated sand and mud of this river, thus prevented from being carried out to sea, would, in the course of years, completely fill up the basin. From some vestiges of the upper carse, as well as of the lower or submarine carse, in situations where their formation cannot easily be traced to any local cause, it seems not improbable that the basin of the German sea itself, nearly as far north as the extent of Scotland, had at one time been occupied with a carse or delta, a continuation of Holland, formed by the accumulation of the {380} diluvium of the rivers which flow into this basin, together with the molluscous exuviæ of the North Sea, and the abrasion of the Norwegian coast and Scottish islands, borne downward by the heavy North Sea swell.