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[Page 9]
This order must be traced & investigated.
If the bulk of elevated ground is considerable, it will be found to consist of a central ridge & of one or more parallel & subordinate ridges which are easily discriminated by their forms & by their constituent strata.
The exterior or lower most ridge usually consists of the more recently formed strata, the next in succession of the Metalliferous & the third or central ridge of the oldest which are often granitical. But these three will be more or less mixed; the strata of the second ridge for instance will often be found imposed on the ore of the central & the strata of the first ridge on those of the second.
These observations however are applicable only to such large chains of Mountains as chiefly determine the forms of Countries, for the smaller chains which intersect them are by no means so composite.
Nor is it to be inferrd [inferred] from what has been said of the larger Chains, that the oldest strata are constantly to be met with in the most elevated positions; on the contrary they often constitute the basis of maritime Countries & Islands.
Elevation therefore is no just criterion of the relative age of the Strata but Infraposition.
For that which is subjacent to every other stratified mass must be the oldest & that which covers every other must be the most recent.
As all Mountains (even the Granitical) are stratified, it is easy to ascertain how far the Strata have been moved out of their original horizontal position
In general they are observed to rise & fall towards the central ridge to which they assertain [ascertain], but in no very uniform manner. It will be usefull [useful] to attend very particularly to this fact.
To this inclination of the Strata & their necessary disruption we are principally indebted for the means