The Annals and magazine of natural history; zoology, botany, and geology . etected by the pebblesand, it may be, extraneous fossils that it will contain. 8. Under ordinary circumstances the river-clay is distinguishedfrom the shore-clay by its immense thickness; for, concentratingto a point the clay of a large area, it accumulates more rapidlythan that resulting from tidal denudation; moreover it is morelikely than any other kind of deposit to be continuous in thesame area through several geological periods. The river-sand 28* 408 Mr. H. G. Seeley on the. Laws which have determined is usually
The Annals and magazine of natural history; zoology, botany, and geology . etected by the pebblesand, it may be, extraneous fossils that it will contain. 8. Under ordinary circumstances the river-clay is distinguishedfrom the shore-clay by its immense thickness; for, concentratingto a point the clay of a large area, it accumulates more rapidlythan that resulting from tidal denudation; moreover it is morelikely than any other kind of deposit to be continuous in thesame area through several geological periods. The river-sand 28* 408 Mr. H. G. Seeley on the. Laws which have determined is usually finer than shore-saud, and extends over a more limitedarea. 9. Sandj clay, and lime forming the sequence of rocks inhorizontal order {i. e. in space), it must also follow that therewill be a similar sequence in vertical order (i. e. in time). Thus,therefore, it follows that if {g) a syenitic coast is denuded, andthe result is {s) sands, (c) clays, and (/) limestones, and the land[g) is depressed so that high-water mark stands at x, then, the Depressed level of land {x).. point from which the deposited materials are derived being car-ried further inland {p), they will not be carried so far out to sea;hence a sand will be deposited near shore and continuous withthe old sand [s); a new clay will be deposited on top of the oldsand [s), and a new limestone on the old clay (c). But if theland were to rise again, the place of origin for the depositedmatter would go further out to sea, the new deposits nearestshore would be denuded, and sand be spread over the clay. If,then, there is a sequence of rocks like the Secondary series, itbecomes extremely easy to determine all the changes in physicalgeography that took place while they were accumulating, whileit is no less easy to predict what must be the representative ofa formation in a district where the mineral characters havechanged. 10. Of course, organic causes and evaporation may accumu-late limestones without their having any relati
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