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[Page 10]
of exploring their contents & their relative position. The principal Vales owe probably their origin to such revolutions.
If a portion of mountainous Country so circumstanced be very regularly stratified, the Strata will shew both the degree & the direction of their inclination in the general form of the superficies, but some Mountains have such an irregular & imperfect stratification that no criterion of this sort can be taken from them.
The most instructive examples in this way are furnishd [furnished] by the compound stratified mountains, some of which will probably occur in the course of the Voyage.
It is owing to the changes which have taken place at very remote periods, in the form & arrangement of the Strata & to the subsequent operation of floods that we find their fracturd [fractured] contents removd [removed] to such a distance in the beds of rivers & in the soil of Vallies, the inspection of which may be considerd [considered] as the first preliminary Step to a knowledge of the constituent Strata of a Country.
To these situations above every other, in the outset of his enquiries, the traveller is referrd [referred] for Geological information. They will be found singularly instructive in regard to the productions of those parts of the interior which he has not the means of visiting.
The discovery of previous stones & of Metallic substances must chiefly be expected in such situations. Of the latter, the most prevalent are Tin & Gold. All these may be detected by their specific gravity & therefore will be found collected in the lowest beds of these alluvial depositions. The force of torrents indeed often expose them but more generally they are discoverd [discovered] iin Mining Countries by regular excavations. The more valuable parts of the Sand are then extracted by Elutrition [elutriation], the particles subsiding in the water according to their proportionate size & their