Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/337

 interesting fauna, which comprises a large number of species, all peculiar to the limited country of which we are speaking. It is necessary, therefore, to admit that there is a Wealden in the Upper as well as in the Lower Chalk.

The repeated alternations which have taken place between truly marine and fluvio-carbonaceous deposits, is a fact well worthy of notice in the history of the Cretaceous formation of the Mediterranean coast. Thus we have ascertained* that the great accumulations of combustible matter of the Province of Ternel, in the Kingdom of Arragon, belong to the Aptian stage. In the Department of the Gard, and at Mondragon, the coal worked belongs to the Middle Chalk. At Sainte Baume† the Provencian limestones contain jet with amber, which has been the object of some research. Lastly, the great industrial works which supply the market of Marseilles with coal are opened in the Santonian and Campanian stages, stages which, in the counties of Kent and Sussex, as well as in the environs of Paris, are remarkable for the purity and whiteness of the chalk of which they are composed.

It would be not merely dangerous, but impossible, to establish a comparison upon the petrographic character of countries distant from each other, since our chalk in the south only furnishes hard limestones employed in large building-works, sandstones with which the streets of Marseilles are paved, black limestone, black clay and coal. But, in spite of this difference in the composition of the rocks, there exists a principle which furnishes a sure means of establishing comparisons, in which mineralogy cannot assist. This principle lies in the examination of the faunas. Thus, although England is deprived of the legion of Rudistes which have rendered the chalk of our country so celebrated, she nevertheless possesses a considerable quantity of fossils identical with ours, by means of which it becomes easy to establish strict synchronisms for the corresponding stages, just as it is easy to show that the chalk of Provence is much more complete than that of Great Britain and the basin of the Seine. Whence I conclude that, if a general classification of the Cretaceous formation were now to be attempted by an international Geological Congress, the preference ought to be given to Provence, on account of the facility of finding there larger and more numerous divisions — in one word, more classical types.

To any one acquainted with the mountains of Provence, the geology of Algeria offers no very serious difficulty. The Cretaceous formation of the elevated plateaux of the Atlas seems to have been copied from Provencal models (fig. 4). Above the Lower Greensand and the Speeton Clay, we find the same succession of stages as in the south of France ; but they are generally richer in fossil species, especially in Ostreoe and Echinoderms.


 * Monographie Paleontologique de l'etage Aptien de l'Espagne, 1862.

† Description Geologique du Massif Montagneux de la Sainte Baume, 1866.