14 Memoir of M. D^ Aubuisson de Voisins. 



observations on the limit of perpetual snow, the variation of 

 culture with the level of the ground, on the height of the 

 most elevated habitation, and lastly, on that dismal plague 

 of mountainous countries, well worthy of the attention of na- 

 turalists, and which engaged the notice of Saussure, cretinism. 

 His observant mind thus embraced all subjects, and seized 

 all the details useful or interesting to science. "With regard 

 to the part strictly geological, what appears most prominent 

 in this memoir, in a general point of view, is the distinctness 

 and force with which he perceived and pointed out the gradual 

 passage of the rocks apparently primordial, into formations 

 which, by their nature and fossils, are unquestionably se- 

 condary ; a result, it is true, ft'om which M. D'Aubuisson de- 

 duced no consequences, except in relation to the formations 

 called primitive ; but which, in reality was, after the beauti- 

 ful work of M. Brochant de Villiers on the Tai'entaise, the 

 second step towards this pi'Ogressive rejuvenescence of the 

 formations of the Alps, continued from that time, and com- 

 pleted in our own day, particularly by geologists of whom 

 also the Corps des Mines has reason to be proud. These ob- 

 servations likewise tended to throw light on the transforma- 

 tion of sedimentary rocks into ci'ystalline rocks, by igne- 

 ous influence, one of the most positive theorems of modern 

 geology, but which was then very strange even to the notions 

 of the author himself. He was led, nevertheless, by his ac- 

 curacy of observation to a conclusion, which the Edinburgh 

 School alone, at that time, began to deduce theoretically from 

 principles of an entirely different nature, and introduce for 

 the first time into the science. 



The work published by M. D'Aubuisson at the same period, 

 on the measurement of heights by the barometer, a work at 

 once theoretical and experimental, is one of those which do 

 him most honour. His abode at the foot of the Alps had 

 furnished him at once with the idea, and the means of acting 

 upon it. "We hive already seen that, in the year 1806, he 

 had turned his attention to the true form and true value to 

 be assigned to the different constructions of the barometrical 

 formula — a formula of which the experiments of Pascal and 

 Mariotte had laid the first foundation ; and which, since 



