Between Poitiers and La Rochelle, the space marked A on the map separates two regions of chalk. This space is occupied by the Oolite and certain other formations older than the Chalk and Neocomian, and has been supposed by M. E. de Beaumont to have formed an island in the Cretaceous sea. South of this space we again meet with rocks which we at once recognise to be cretaceous, partly from the chalky matrix and partly from the fossils being very similar to those of the white chalk of the north: especially certain species of the genera Spatangus, Ananchytes, Cidarites, Nucula, Ostrea, Gryphæa (Exogyra), Pecten, Plagiostoma (Lima), Trigonia, Catillus (Inoceramus), and Terebratula.[[4]] But Ammonites, as M. d’Archiac observes, of which so many species are met with in the chalk of the north of France, are scarcely ever found in the southern region; while the genera Hamite, Turrilite, and Scaphite, and perhaps Belemnite, are entirely wanting.

Fig. 276: Hippurites organisans. Upper chalk:—chalk marl of Pyrenees?[[5]]

On the other hand, certain forms are common in the south which are rare or wholly unknown in the north of France. Among these may be mentioned many Hippurites, Sphærulites, and other members of that great family of mollusca called Rudistes by Lamarck, to which nothing analogous has been discovered in the living creation, but which is quite characteristic of rocks of the Cretaceous era in the south of France, Spain, Sicily, Greece, and other countries bordering the Mediterranean. The species called Hippurites organisans (Fig. 276) is more abundant than any other in the south of Europe; and the geologist should make himself well acquainted with the cast of the interior, d, which is often the only part preserved in many compact marbles of the Upper Cretaceous period. The flutings on the interior of the Hippurite, which are represented on the cast by smooth, rounded longitudinal ribs, and in some individuals attain a great size and length, are wholly unlike the markings on the exterior of the shell.

Cretaceous Rocks in the United States.—If we pass to the American continent, we find in the State of New Jersey a series of sandy and argillaceous beds wholly unlike in mineral character to our Upper Cretaceous system; which we can, nevertheless, recognise as referable, palæontologically, to the same division.

That they were about the same age generally as the European chalk and Neocomian, was the conclusion to which Dr. Morton and Mr. Conrad came after their investigation of the fossils in 1834. The strata consist chiefly of green sand and green marl, with an overlying coralline limestone of a pale yellow colour, and the fossils, on the whole, agree most nearly with those of the Upper European series, from the Maestricht beds to the Gault inclusive. I collected sixty shells from the New Jersey deposits in 1841, five of which were identical with European species—Ostrea larva, O. vesicularis, Gryphæa costata, Pecten quinque-costatus, Belemnitella mucronata. As some of these have the greatest vertical range in Europe, they might be expected more than any others to recur in distant parts of the globe. Even where the species were different, the generic forms, such as the Baculite and certain sections of Ammonites, as also the Inoceramus (see [Fig. 252]) and other bivalves, have a decidedly cretaceous aspect. Fifteen out of the sixty shells above alluded to were regarded by Professor Forbes as good geographical representatives of well-known cretaceous fossils of Europe. The correspondence, therefore, is not small, when we reflect that the part of the United States where these strata occur is between 3000 and 4000 miles distant from the chalk of Central and Northern Europe, and that there is a difference of ten degrees in the latitude of the places compared on opposite sides of the Atlantic. Fish of the genera Lamna, Galeus, and Carcharodon are common to New Jersey and the European cretaceous rocks. So also is the genus Mosasaurus among reptiles.

It appears from the labours of Dr. Newberry and others, that the Cretaceous strata of the United States east and west of the Appalachians are characterised by a flora decidedly analogous to that of Aix-la-Chapelle above-mentioned, and therefore having considerable resemblance to the vegetation of the Tertiary and Recent Periods.

[1] For particulars of structure see [p. 318.]

[2] Geol. Trans., 1st Series, vol. iv, p. 413.