"A cette vue, je fus sur le champ et irrésistiblement entrainé à penser, (comme l'auroit été sans doute tout connoisseur impartial frappé des conséquences de ce phénomène;) je fus, dis je, irrésistiblement entrainé aux id es suivantes: Ce _basalte_, cette _wacke_, cette _argile_, et ce _sable, sont d'une seule et même formation_; ils sont tous l'effet d'une _precipitation par voie humide_ dans une seule et même submersion de cette contrée; les eaux qui la couvroient alors transportoient d'abord le _sable_, puis deposoient l'_argile_, et changoient peu-à-peu leur précipitation en _wacke_, et enfin en vraie _basalte_.--Journal de Physique, tom. xxxviii. (1791,) Partie i. p. 415.] First, as to the sand on the top of this basaltic hill, it is most probably the remains of certain sandstone strata that originally covered the basaltic part, but are now worn away. We are therefore to consider this as an instance of a basaltic rock, interposed between strata that are undoubtedly of marine origin. In this, however, there is nothing inconsistent with Dr Hutton's theory of basaltes; on the contrary, it is one of the principal facts on which that theory is founded. It has indeed been argued by some mineralogists, that bodies thus contiguous must owe their origin to the same element, and that a mineral substance cannot be of more recent formation than that which lies above it. But the maxim, that a fossil must have the same origin with those that surround it, does not hold, unless they have a certain similarity of structure. It is, for instance, the want of this similarity, that authorizes us to assign different periods of formation to mineral veins, and to the rocks in which they are included. In a succession of strata, no one can doubt, that the lowest were the first formed, and the others in the order in which they lie; but, when between two strata of sandstone or of limestone we find an intermediate rock, so different as to resemble lava, and to have nothing schistose or stratified in its composition, the same instrument cannot be supposed to have been employed in the formation of both; nor is there any reason why we may not suppose, that the intermediate body was interposed between the other two, by some action subsequent to their formation. It was thus that Dolomieu concluded, when he saw a lava-like stone interposed between calcareous strata in the Val di Noto, that, though contiguous, these two rocks could not possibly be of the same formation; and thus far it is certain, that every unprejudiced observer must agree with him. 251. But the circumstance on which Werner seems to lay the greatest stress, is the gradual transition from the sand to the basalt, through the intermediate steps of clay and wacke; this gradual transition he considers as a direct proof, that they are all of the same formation.