Along the sea-shore, to the east of Brighton, there is a bank of sand and calcareous mud, the detritus of the neighbouring cliffs, in the progress of formation; and in this sediment Mr. Reginald Mantell discovered recent Rotaliæ, Nodosariæ, &c., with frustules of Bacillariæ, Coscinodisci, Naviculæ, and other diatomaceæ; associated with cretaceous polythalamia washed out of the chalk,[345] The difference in the aspect of the recent and fossil organisms was so evident, as to leave no doubt of the correctness of this interpretation. Here, then, at the present moment, a deposit is going on, whose organic contents consist of an assemblage of species of living animalcules of our seas, with the fossil forms of the ancient chalk ocean; in like manner as in the bed of the Nile, the Nummulites of the tertiary rocks are being imbedded with the existing mollusks and desmidiæ of that river (ante, [p. 345].).
GEOLOGICAL DISTRIBUTION OF THE FORAMINIFERA.
Geological distribution of the Foraminifera.—According to the observations of M. D'Orbigny, the first appearance of the tribes of minute beings which have played so important a part in the elaboration of materials for the formation of the sedimentary rocks of the secondary and tertiary ages, and are at this moment invisible but powerful agents in the accumulation of calcareous sediments at the bottom of the sea, was in the Carboniferous epoch, and by a single type, the Fusulina (ante, [p. 346].). I believe no certain evidence of the occurrence of Foraminifera in Silurian or Devonian deposits has been obtained.
M. D'Orbigny gives the following summary of the distribution of the known fossil and recent species:—
| GENERA. | SPECIES. | |
| Carboniferous System | 1 | 1 |
| Jurassic | 5 | 20 |
| Cretaceous | 34 | 280 |
| Tertiary | 56 | 460 |
| Living in the present Seas | 68 | 1000 |
| Of the recent species, | 575 | inhabit the | Tropics. |
| ——— | 350 | —— | Temperate zones. |
| ——— | 75 | —— | Cold regions. |
The above statistical view was published six years ago; but the great activity of research that has since prevailed, has largely augmented the known number both of fossil and recent forms. M. D'Orbigny's recent Tables[346] give for the Jurassic or Oolite 10 genera; Cretaceous, 38 genera; Tertiary, 60 genera; but this estimate must be far too low.
[346] Cours Elémentaire de Paléontologie.