Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/109

 Rh or vice versa, that of flint into chalk. The following reductions of Saussure on this subject are strongly in point. — “ These observations and these experiments appear to me to prove that the intermediate species which have been sometimes considered as forming the gradation from one genus to another, or as limestones partly transformed into flint, are very often merely mechanical mixtures of the two. In fact there is no mineral hitherto known which we might not assume as the commencement of a series, and thence proceed to establish by insensible shades a circuit comprehending the whole of those which have been already determined, and the more extensive our acquaintance with mineralogy the more will the truth of the observation become apparent, in consequence of the more numerous varieties and shades of difference which will be discovered.“

It would appear however that the chalk in which flints occur, although subordinate to the calcareous rocks, must, according to Brongniart, belong to a formation anterior to that of the limestone which he denominates grossière. He asserts that the fossils found in chalk are almost all species of extinct genera, and that the situation of chalk is always inferior to that of the calcaire grossier. It is probably this species of limestone of which the quarry of St. Eutrope, near Aix in Provence consists, where the Chevalier de Sades affirms, eleven beds have been formed since the existence of man in a civilized state?

The western border of Dorsetshire is nearly the limit of the occurrence of flints in the chalk. This last, however, extends on the road to Axminster, to within four miles of Honiton in Devonshire, where