Discussion.
Mr. J. W. Flower called attention to the great discrepancy between the thickness of the Cretaceous beds of the south of France and those of England, the former being four times the magnitude of the latter. This was principally made up by several strata entirely wanting in England, and for the most part of a totally different character, being either of freshwater origin or else hippurite limestone. Another great feature of distinction was the presence of coal-bearing beds with numerous layers of lignites. That these beds were of Cretaceous origin was proved by their occurrence under undoubted Eocene beds. Among the fossils of the Algerian chalk were those of several genera unknown in the Cretaceous beds of England.
Dr. Duncan suggested that possibly the Upper Coal-beds might be the equivalents of those of Aix-la-Chapelle. He doubted whether any decided synchronism in strata spread over so extensive an area as that of the Cretaceous deposits could be established by the mere occurrence of certain fossils in them; nor could he attach much value to supposed specific differences in shells of such character as Ostrea. The variations in condition in the sea-bottom would lead to variations in the Testacea ; and there were signs to be found of great variations going on before the form of Hippurites was developed. He regarded Hippurites as a modified form of Chama or Caprina, and thought it was parasitic on coral, reefs in the same way as its modern representative. He accounted for its presence by the great development of corals at that period in the Cretaceous seas.
Mr. Judd remarked upon the repeated changes which had occurred in the opinions of foreign geologists as to the limits of the various "stages" into which the Cretaceous rocks might be divided, and indicated that this of itself was equivalent to the abandonment of the principles laid down by D'Orbigny. He further observed that in the recent changes, even as evidenced by M. Coquand's paper, there was a tendency to approach the views as to the classification of the Cretaceous beds established by the late Prof. Edward Forbes, and generally accepted by English geologists.
Prof. Morris observed that the object of the French geologists had been to remove the opinion that mere mineralogical characters were sufficient to distinguish Cretaceous strata. He called attention to the existence of copper and antimony in some of the Lower Cretaceous beds, and to the great break that appeared to exist between the Lower and Middle Cretaceous series. Another curious point was that in the south of France there appeared to be passage-beds between the Upper Cretaceous and Eocene beds.
Prof. T. RUPERT Jones remarked on the analogy between the passage from the Chalk to the Eocene Tertiaries, as supposed to be exhibited in the south of France and in the Nebraska territory of America. He pointed out that as the Cretaceous beds of France had been deposited, not in one sea, but in separate sea areas, they were, of course, difficult of correlation.
