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are exceeding rare, and must, like manyothers, be made in the rivers themselves, asin the canals in Holland, or at theirmouths, and there is no reason to thinkthat it is the vegetable matter that dis-colours some rivers that is ever deposited,but the more solid turfy particles that arecarried off by the rivers that flow throughbogs or the particles that accidently fallinto them ; the vegetable matter found inthe canals of Holland does not form a par-ticular stratum, but is mixed with mud,no such stratum has been found in the ex-cavation made in Holland to the depth of240.feet, as may be seen in Varenius andMuschenbroeck, nor in that made in thestrata formed by the depositions of the Seineexamined by Guettard, Mem. Par. 1753.nor in that made in Egypt, though thefoil was intirely formed of the depositionsfrom the Nile, nor has any such coalymatter been ever brought up in any sound-ings ; hence I conclude that the existenceof such strata at the bottom of the sea ispurely imaginary.

3 . Is our beds of mineral coal had beenformed in the sea, we should find sea shells

among