186 SUPPLEMENTAUY NOTES. 



body being in general siliclfied, and the most delicate internal structure preserved. Shells, 

 corals, and the minute cases of foraminifera, are often immersed as it were in pure flint, appearing 

 as if preserved in a semi-transparent medium. 



But there are innumerable flint nodules in which no traces of spongeous tissue are apparent, 

 and veins, dikes, and sheets of tabular flint, that are in a great measure free from organic 

 remains ; containing only such as may be supposed to have become imbedded in a stream of 

 fluid silex that flowed over a sea-bottom. VYood perforated by lithodomi and silicified, is 

 occasionally met with ; and fuci or algEe are sometimes found, appearing as if floating in the 

 liquid flint. 



For the most part, the minute shells in the chalk and flint are fllled with amorphous mineral 

 matter ; but in many examples, (as I have ascertained by direct experiment,) the soft parts of 

 foraminifera remain in the shell. 



XII. Foraminifera. — Plate LXII. contains figures of several species belonging to various 

 genera of those minute fossil shells, the discoidal involute forms of which were once considered 

 to belong to the Cephalopoda, and to be related to the Nautilus, Spirula, &c., but which are now 

 grouped in one family, under the name of Foraminifera ; a term derived from the foramina or 

 perforations with which their shells are traversed, and which have relation to the peculiar 

 organization of the animals. 



Since microscopic observations have become so general, thanks to the genius and enthusiasm 

 of Ehrenberg, these fossil bodies have acquired a degree of interest and importance, unsurpassed 

 by more obvious organic remains. Whole mountain chains and extensive tracts of country are 

 now known to be almost entirely composed of the aggregated shells of a few genera of these 

 microzoa.^ In other deposits their remains are associated with those of Infusoria^ (both animal 

 and vegetable,) still more infinitesimal. As much error prevails among collectors as to the 

 real nature of the fossil foraminifera, I am induced to annex the following remarks.' 



The foraminifera are marine animals of low organization, and, with but few exceptions, 

 extremely minute : in an ounce of sea-sand between three and four millions have been distinctly 

 enumerated. When living, they are not aggregated, but always individually distinct ; they are 

 composed of a body (or vital mass) of a gelatinous consistence, which is either entire, and round, 

 or divided into segments, placed either on a simple or alternate line, or coiled spirally, or 

 involuted round an axis. This body is covered with an envelope or shell, which is generally 

 testaceous, rarely cartilaginous, and is modelled on the segments, and follows all the modifications 

 of form and contour of the body. From the extremity of the last segment, there issue, sometimes 

 from one, sometimes from several openings of the shell, or through numerous pores or foramina, 

 very elongated, slender, contractile, colourless filaments, more or less divided and ramified, 

 serving for prehension, and capable of entirely investing the shell. The body varies in colour, 

 but is always identical in individuals of the same species, — it is yellow, fawn-coloured, red, 



' A conTenient term to express animal organisms that can only be distinctly examined by the aid of the microscope : 

 strata in a great measure composed of such fossil remains may be distinguished as microzoia deposits. 



^ This term was first employed to denote the various minute forms of animal organization that appear in vegetable 

 infusions ; as Rotifers, Monads, Vorticella, &c. But with these, numerous vegetable forms generally appear, as Graillonella, 

 Bacellaria, !N"avicula, &c. : these were formerly also regarded as animals, and were consequently comprised under the same 

 general appellation. 



' The best scientific account of these animals wiU be found in M. D'Orbigny's work on the " Foraminiferes Fossiles du 

 Bassin Tertiaire de Vienne, (Autriche)." Paris, 18i6. 1 vol. 4to, with plates. 



