The Foraminifera (save Gromia, which occurs in both fresh and salt water, and the fresh-water forms allied to this) are marine, and are found in almost all seas, though more abundantly in those of the warmer parts of the globe. It is concluded by Dr Carpenter that "the foraminiferous fauna of our own seas probably presents a greater range of variety than existed at any preceding period; but there is no indication of any tendency to elevation towards a higher type." One of the most remarkable facts about their distribution at the present day, is the existence of a deposit at great depths in the Atlantic and Pacific oceans, in areas traversed by warm currents, of a mud or "ooze" formed almost entirely of the shells of Foraminifera, and principally of Globigerinae (fig. 15). This "Globigerina ooze" is found up to depths of 3000 fathoms, and may be regarded as the modern analogue of the white Chalk of the Cretaceous period. The deep-sea dredgings of late years have further brought to light an immense number of forms of "arenaceous" Fora-minifera of the most varied and interesting characters. Some of the living Foraminifera may be obtained, at or near low-water mark, adhering to the roots of tangle; but they are mostly to be obtained by dredging in deeper water, or by the tow-net, or by search in the shelly sand of the sea-shore.
Fig. 15. - Organisms in the Atlantic ooze, chiefly Foraminifera (Globigerina and Textularia), with Polycystina, and Sponge - spicules ; highly magnified. (Original.)
Most of the recent Foraminifera are very minute, often wholly microscopic in their dimensions; but some of the extinct forms attained the size of as much as three inches in circumference (e.g., the Nummulites of the Eocene, fig. 16), and the spheres of the Cretaceous Parkeria may have a circumference more than twice as great as this.