368. These arguments appear to me conclusive against the necessity of supposing the action of sudden and irregular causes on the surface of the earth. In this, however, I am perhaps deceived: neither Pallas, nor Saussure, nor Dolomieu, nor any other author who has espoused the hypothesis of such causes, has explained his notions with any precision; on the contrary, they have all spoken with such reserve and mystery, as seemed to betray the weakness, but may have concealed the strength of their cause. I have therefore been combating an enemy, that was in some respects unknown; and I may have supposed him dislodged, only because I could not penetrate to his strongholds. The question, however, is likely soon to assume a more determinate form. A zealous friend of Dr Hutton's theory, has lately[185] declared his approbation of the hypothesis which has here been represented as so adverse to that theory; and, from his ability and vigour of research, it is likely to receive every improvement of which it is susceptible. [Footnote 185: Trans. Royal Society Edin. vol. v. p 68.] NOTE XIX. § 117. _Transportation of Materials by the Sea._ 369. THE existence of the great and extensive operations, by which the spoils of the land are carried all over the ocean, and spread out on the bottom of it, may be supposed to require some further elucidation. We must attend, therefore, to the following circumstances. When the detritus of the land is delivered by the rivers into the sea, the heaviest parts are deposited first, and the lighter are carried to a greater distance from the shore. The accumulation of matter which would be made in this manner on the coast, is prevented by the farther operation of the tides and currents, in consequence of which the substances deposited continue to be worn away, and are gradually removed farther from the land. The reality of this operation is certain; for otherwise we should have on the sea shore a constant and unlimited accumulation of sand and gravel, which, being perpetually brought down from the land, would continually increase on the shore, if nature did not employ some machinery for removing the advanced part into the sea, in proportion to the supply from behind.