589
13. In the higher secondary rocks, which border on primitivemountains, the strata are usually more or less inclined, and some-times even vertical. But in hills of more moderate elevation, and inthe lower and most level parts of the earth, the strata of secondaryrocks are in general nearly or quite horizontal.
14. If these horizontal strata be penetrated in the vicinity of thehigher and inclined strata, the former will always be found lying overor covering the latter. The same fact occurs, when the examinationis made in level countries at a distance from the inclined strata ; but,in the latter case, it is necessary to penetrate to a much greater depthto discover the inclined or primitive strata.
15. It is hence obvious, that the higher and inclined strata do notrest upon the lower and horizontal strata; but, on the contrary, thehorizontal strata are usually placed upon the declivities of the higherand inclined strata. For the inclined strata of the higher secondaryrocks so decline as to pass under the horizontal strata ; and the high-est strata of primitive rocks do in fact so slope and decline, as to passunderneath all the secondary strata.
It is also obvious, that those rocks, which have the lowest level,when referred to the sea or the general level of the country, are ofthe most recent formation; for they really lie over all the otherrocks.
16. It is further evident, that the higher the level, at which anyrock appears at the surface of the earth, the older is that rock ; forit so declines as to pass under those rocks, which appear at a lowerlevel.—The only exception to this general fact appears in those hori-zontal strata of secondary rocks, which sometimes rest on the sum-mits of high mountains.
17. Primitive rocks, whether constituting the naked summits ofhills and mountains, or covered by secondary rocks, have never ex-hibited any organic remains of animals or vegetables.—Hence theywere undoubtedly formed before the existence of organized bodies.
18. But in the higher and older secondary rocks the remains ofmarine animals and marine plants begin to appear. These remainsare, in general, well preserved, and belong to species and even gene-ra, which do not exist in modern seas, nor even in the more recent ofthe secondary rocks.
19. As the strata become newer, the shells, which existed in theolder secondary rocks, gradually give place to new species and gen-era of shells and other marine, organic remains ; and in the most re-cently formed strata are found species of shells, &c. perfectly resem-bling those, which at present exist in the ocean. Remains and im-pressions of vegetables, belonging to dry land, are not uncommon ;