The three systems we have spoken of are not the only works which have been composed on the theory of the earth; a Memoir of M. Bourguet appeared in 1729, printed at Amsterdam, with his "Philosophical Letters on the Formation of Salts, &c." in which he gives a specimen of the system he meditated, but which was prevented completion by the death of the author. It is but justice to admit, that no person was more industrious in making observations or collecting facts. To him we owe that great and beautiful observation, the correspondence between the angles of mountains. He presents every thing which he had collected in great order; but with all those advantages, it appears that he has succeeded no better than the rest in making a physical and reasonable history of the changes which had happened to the globe, and that he was very wide from having found the real cause of those effects which he relates. To be convinced of this we need only cast our eyes on the propositions which he deduces from the phenomena, and which ought to serve for the basis of his theory. He says, that the whole globe took its form at one time, and not successively; that its form and disposition prove that it has been in a state of fluidity; that the present state of the earth is very different from that in which it was for many ages after its first formation; that the matter of the globe was at the beginning less dense than since it altered its appearance; that the condensation of its solid parts diminished by degrees with its velocity, so that after having made a number of revolutions on its axis, and round the sun, it found itself on a sudden in a state of dissolution, which destroyed its first structure. This happened about the vernal equinox. That the sea-shells introduced themselves into the dissolved matters; that after this dissolution the earth took the form it now has, and that the fire which directly infused itself therein consumed it by degrees, and it will be one day destroyed by a terrible explosion, accompanied with a general conflagration, which will augment the atmosphere of the globe, and diminish its diameter, and that then the earth, instead of beds of sand or earth, will have only strata of calcined metal and mountains composed of amalgamas of different metals. This is sufficient to shew the system M. Bourguet meditated; to divine in this manner the past, and predict the future, nearly as others have predicted, does not appear to me to be an effort of judgment: this author had more erudition than sound and general views: he appears to be deficient in that capaciousness of ideas necessary to follow the extent of the subject, and enable him to comprehend the chain of causes and effects.