Note 12 — Chapter I · (continued 3)
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Footnote 12:
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We are not however to estimate this operation, of forming soil by the muddy waters of a river depositing sediment, in the manner that M. de Luc has endeavoured to calculate the short time elapsed in forming the marshlands of the Elbe. This philosopher, with a view to show that the present earth has not subsisted long since the time it had appeared above the surface of the sea, has given an example of the marsh of Wisebhafen where the earth, wasted by inundation, was in a very little time replaced, and the soil heightened by the flowings of the Elbe, and this he marks as a leading fact or principle, in calculating the past duration of our continents, of which he says, we are not to lose sight (Tome 5, p. 136.) But here this philosopher does not seem to be aware, that he is calculating upon very false grounds, when he compares two things which are by no means alike, the natural operations of a river upon its banks, making and unmaking occasionally its haughs or level lands, that is to say, alternately making and destroying, and the artificial operations of man receiving the muddy water of a tide-way into the still water of a pond formed by his ramparts; yet, it is by this last operation that our author forms an estimate which he applies to the age of this earth, in calculating how long time might have been required for producing the marsh lands of the Elbe.
I would here ask if he can calculate what time it may have required to hollow out the bed of the Elbe from its source to the sea; and to tell how often the marsh-lands, which he now sees cultivated, had been formed and destroyed by the river before they were cultivated in their present state; or if there is any security that they shall not again be taken away by the river, and again formed in the same place. If this is the case, that the river is constantly changing the fertile lands, which it forms by its inundation, what judgement are we to form by calculating the quantity of sediment in a certain measure of its muddy water.