it is considered,
that, from Portland to Caithness or the Orkneys, there are at least ten
different productions of hard stone in the solid land which are placed
at proper distances, are perfectly distinguishable in the gravel which
is formed of them, and with all of which I am well acquainted. Let us
suppose the distance to be 600 miles, and this to be divided equally
into 10 different regions of 60 miles each, it must be evident that we
could not only tell the region, which is knowing within 60 miles of the
place, but we could also tell the intermediate space, by seeing an equal
mixture of the gravel of two contiguous regions; and this is knowing
within 30 miles of the place. If this be allowed, it will not seem
difficult to estimate an intermediate distance from the different
proportions of the mixed gravel. This is supposing the different regions
to be in all respects equal, which is far from being in reality the
case; nevertheless, a person well acquainted with the different extent
and various natures of those regions, may make allowances for the
different known circumstances that must have influenced in those
operations, although it is most probable there will be others which must
be unknown, and for which he can make no allowance.

The author of the Tableaux de la Suisse has entered very much into this
view of things; he has given us some valuable observations in relation
to this subject, which I would here beg leave to transcribe[7].

[Footnote 7: Discours sur l'Histoire Naturelle de la Suisse, p. 27.]

"Nous avons dit precedemment que c'etoit entre Orfiere et Liddes que
nous avions vu les derniers granites roules, on n'en rencontre plus dans
tout le reste de la route jusqu'au haut du Mont St. Bernard. Les rochers
qui dominent ce sommet ne sont pas composes de granites, et quoiqu'on
ne puisse aborder jusqu'a leur plus grande elevation, on peut juger de
leurs especes, par les masses qui s'en precipitent. D'ou peuvent donc
provenir ces masses roulees de granites qui se trouvent jetes et
repandus sur le penchant et au bas de ce mont? Il y a peut-etre quelque
montagne ou rocher de granite que nous n'avons pas ete a portee de voir:
il faudroit plus d'un mois pour faire un pareil examen et parcourir
les montagnes environnantes, et faute de pouvoir parvenir a certains
sommets, examiner scrupuleusement les fonds pour juger des hauts. De
pareilles recherches sont plus difficiles et plus longues qu'on ne le
croit commune