The view which I take of the subject is this; first, that those water-worn materials had their great roundness from the attrition occasioned by the waves of the sea upon some former coast. Secondly, that, after having been thus formed by agitation on the shores, and transported into the deep, this gravel had contributed to the formation of secondary strata, such as the puddingstone which has been described in Part I. Chap 5, and 6; and, lastly that it has been from the decay and resolution of those secondary strata, in the wafting operations of the surface, that have come those rounded siliceous bodies, which could not be thus worn by travelling in the longest river.] I do not know in what manner M. Gensanne made his calculation; I would suspect it was from partial, and not from general observations. We have mountains in this country, and those not made of more durable materials than what are common to the earth, which are not sensibly diminished in their height with a thousand years. The proof of this are the Roman roads made over some of those hills. I have seen those roads as distinct as if only made a few years, with superficial pits beside them, from whence had been dug the gravel or materials of which they had been formed. The natural operation of time upon the surface of this earth is to dissolve certain substances, to disunite the solid bodies which are not soluble, but which, in having been consolidated by fusion, are naturally separated by veins and cutters, and to carry those detached bodies, by the mechanic force of moving water, successively from stage to stage, from places of a higher situation to those below. Thus the beds of rivers are to be considered as the passages through which both the lighter and heavier bodies of the land are gradually travelling; and it is through them that those moveable bodies are from time to time protruded towards the sea shore. But, in the course of rivers, it often happens that there intervenes a lake; and this must be considered as a repository for heavy bodies which had been transported by the force of running water, in the narrow bed through which it was obliged to pass; for, being arrived in the lake, the issue of which is above the level of its bottom, the moving water loses its force in protruding heavy bodies, which therefore it deposits. Thus the bottom of the lake would be filled up, before the heavy materials which the river carries could be made to advance any farther towards the sea.