Upper Chalk of Western Europe, the Tertiary beds, and at the present day in the Atlantic ; but it has not been found in the Lower Cretaceous rocks of Europe, though representatives of it (P. Karsteni, &c.) are not wanting in some of the Secondary formations. P. elegans, another old (Secondary) form, reached a high stage of growth and abundance in the sea that deposited the Gault of England and Europe, and has continued since.
Discorbina has presented no fossil form older than the Upper Chalk (Maestricht). Since the Cretaceous period it has abounded profusely in the Paris Tertiaries, and in many other localities since ; and it still flourishes.
Rotalia is found in the Gault ; but it seems to have flourished more abundantly in seas of later periods, and is prolific now in the Atlantic and elsewhere.
Of the other Rotalinoe, we have not sufficient data for correct observation in the line of research we have here pursued ; except that we may note the isolated occurrence of Cymbalopora at Maestricht, and its apparent absence until the Miocene period, the absence of Calærina and of Orbitoides before the Chalk, and, on the other hand, the persistence of Tinoporus and Patellina through the Cretaceous and Tertiary to the present age.
With the Rotaline, as with Globigerina (of which we intend to treat before long), the chief distinction between the Cretaceous and existing groups is in the progressively increased number of modifications, and among them the incoming of important variations, though few of them are of generic, or even specific, value, — a distinction strong enough, when supported by other known geological and palaeontological considerations, to mark the impropriety of calling the Atlantic ooze " Chalk," except in the sense of a calcareous rock of marine organic origin. That its geological status should not be spoken of in this vague halobiolithological[1] sense, the painstaking and thoughtful Ehrenberg long ago warned us. He says:—"In consequence of the mass-building Infusoria and Polythalamia [Diatoms, Polycystines, and Foraminifers], the Secondary formations can now no longer be distinguished from the Tertiary ; and, in accordance with what has been above stated, masses of rock might be formed even at the present time in the ocean, and be raised by volcanic power above the surface, the great mass of which would, as to its constituents, perfectly resemble the Chalk. Thus, then, the Chalk remains still to be distinguished as a geological formation, but no longer as a species of rock by its organic contents." 'Taylor's Scientific Memoirs,' vol. iii. 1843, p. 367, § 10 ; ' Edinb. New Phil. Journ.' vol. xxxiv. 1843, p. 260 ; Abhandl. Berl. Akad. für 1839, p. 164, 4to, 1841.
To render our synoptical study of the Rotalinæ more complete, we propose to compare the oldest forms on some future occasion ; and, for the present, we offer, in a Supplement to this paper, a critical examination and revised nomenclature of such Tertiary Rotalinæ as have been figured and described by Reuss, Bornemann, Karrer, and other palaeontologists, and are not included in the foregoing lists.
- ↑ "Halobiolith" (Ehrenberg) is a stratum of marine organic origin.
