It is singularly fortunate that such remarkable appearances, as are found in the rocks of this place, had called the attention of M. de Saussure to investigate a subject so interesting to the present theory; and it is upon this, as well as on many other occasions, that the value of those observations of natural history will appear. They are made by a person eminent for knowledge; and they are recorded with an accuracy and precision which leaves nothing more to be desired. From _Martigny_ to _St. Maurice_, about three leagues, there is a most interesting valley of the Rhône, through which this river makes its way from the _Vallais_, or great valley above, among those mountains which seem to have shut up the _Vallais_, and through which the river must pass in running to the lake. M. de Saussure found some singular masses, which attracted his attention, in examining the structure of the rocks on the left side of this little valley. Like a true philosopher, and accurate naturalist, he desired to compare what was to be observed in the other side of this valley of the Rhône, which he had found so singular and so interesting on that which he had examined. Accordingly, in Spring 1785, he made a journey for that purpose. In this survey he found the most perfect correspondence between the two sides of this valley, so far as rocks of the same individual species, and precisely in the same order, are found upon the one side and upon the other. This author, after describing those particular appearances, sums up the evidence which arises from this comparison of the two sides of the valley; and he here gives an example of just reasoning, of accuracy, and impartiality, which, independent of the subject, cannot be read without pleasure and approbation. But when it is considered, that here is a matter of the highest importance to the present theory, or to any other system of geology, no less than a demonstration that the rocks, of which the mountains on both sides of the valley of the Rhône are formed, are the same, and must have been originally continued in one mass, the following observations of our author will be most acceptable to every person who inclines to read upon this subject. «§ 1079. On voit par cet exposé, que bien que la vallée du Rlione ait dans ce trajet près d'une lieue de largeur moyenne, les montagnes qui la bordent sont en general du même genre, et dans la même situation sur l'une et l'autre rive. «Il y a cependant trois différences que je dois exposer et apprécier en peu de mots.