They had no such effect upon him. He left St. Louis as soon as ever he obtained the assent of the Governor, Fleuriau, to his proposal to explore the sources of the great rivers of Senegambia, and especially those of the Djoliba.

This subject is the more worthy of being investigated, since it is generally interesting to the geology of volcanoes; and since that excellent mineralogist, M. Fleuriau de Bellevue, after having examined Italy and the adjacent islands with great attention, affirms, that it is highly improbable that pumice-stone owes its origin to the swelling of obsidian.