p. 234.), not larger than a grain of sand. In short, the tertiary sands and marls, very generally contain immense numbers of this class of organic remains. But no specimens of the British tertiary that have come under my notice, are at all comparable with those of Germany, and other countries on the continent, and in the United States.

The POLIERSCHIEFER (polishing-slate) of Bilin, is stated, by M. Ehrenberg, to form a series of strata fourteen feet in thickness, entirely made up of the siliceous shells of Gaillonellæ, of such extreme minuteness, that a cubic inch of the stone contains forty-one thousand millions! The Berghmehl (mountain-meal, or fossil farina) of San Fiora, in Tuscany, is one mass of animalculites. In Lapland a similar earth is found, which, in times of scarcity, is mixed by the inhabitants with the ground bark of trees, for food; some of this earth was found to contain twenty different species of fossil animalcules. In the district of Soos, near Egra, in Bohemia, a fine white infusorial earth occurs, about three feet beneath the surface; this substance, when dried, appears to the naked eye, like pure magnesia, but, under the microscope, is seen to be entirely constituted of an elegant species of infusorial carapace, (named Campilodiscus,) of which figures are given, Lign. 51, figs. 1, 2.*

* I am indebted to H. Hopley White, Esq. of Clapham, for specimens of this and other infusorial earths from Germany.

INFUSORIAL MARL OF RICHMOND, IN VIRGINIA.— The town of Richmond, in Virginia, is built on strata of siliceous marls of great extent, which

Fig. 1.-NAVICULA. la. Side view.

2.-COSCINODISCUS RADIATUS; a portion of the circular
shield.

3.-GAILLONELLA SULCATA. The upper figure shows the
face of one of the joints or animalculites.

3a. Three of these animalculites united.

4, 5.-ACTINOCYCLUS. Two species.

6.-COSCINODISCUS PATINA. Front and side views.

have a total thickness, beneath and around the

town, of more than twenty feet.

These marls,

whose composition was first detected by Professor

W. B. Rogers, are referred, by that eminent American geologist, to the older tertiary (eocene, or miocene) formations. They occupy considerable districts, spreading out into sterile tracts, along the flanks of the hills, their siliceous character rendering them unfavourable to vegetation. The investigations of Dr. Bailey have shown that the siliceous skeletons, so abundant in this earth, consist of several species of Navicula (Lign. 48, fig. 1, 1 a.), Gaillonella (Lign. 48, fig. 3, 3 a.), Actinocyclus (Lign. 48, figs. 4, 5.), &c.

The most remarkable forms are saucer-shaped shells or discs, having their surfaces elaborately ornamented with hexagonal spots disposed in curves, presenting some resemblance to the engine-turned case of a watch. Lign. 48, fig. 2, is a small segment of a disc, very highly magnified. These discs vary in size from 100 to 1000 of an inch in diameter: they are named Coscinodiscus (sieve-like disc), and there are several species: one less richly sculptured, C. patina, is figured Lign. 48, fig. 6.

1

1

Circular bodies, with five or six lines radiating from the centre to the circumference, like the spokes of a wheel, hence named Actinocyclus, (Lign. 48, figs. 4, 5.), are also abundant; and spicula of sponges, Alcyonia, and probably of Actiniæ.

When a few grains of this marl are prepared, and mounted on a glass, almost all these varieties will be manifest, so largely is this earth composed of the skeletons of animalcules; in fact, very few

inorganic particles are intermixed with the organisms. The merest pellicle or stain, left by the evaporation of a drop of water in which some of the marl has been mixed, teems with the most beautiful infusorial structures.

At Petersburg, in Virginia, an infusorial sandy marl occurs, interstratified with deposits which, from their shells, are referred to the older tertiary formations. Probably this marl is a continuation of that of Richmond, but it is full of many new forms, associated with those common in the earth of the latter locality. Dr. Bailey has favoured me with specimens which surpass, in the variety, elegance, and interest of their fossil contents, any infusorial deposits I have examined.*

Mr. Edwin Quekett, whose talents and acquirements as a naturalist are of the highest order, has detected in a recent state, attached to some zoophytes preserved in spirits, and brought from Melville Island by Sir Edward Parry, several discs resembling the Coscinodiscus radiatus, figured Lign. 48. These are in pairs, and there is no doubt that the fossil cases, like the recent, belonged to bivalve infusoria. Gaillonellæ, Pyxidiculæ, Naviculæ, and other forms resembling those of the Richmond earth, were also

* Dr. Bailey, with great liberality, has so amply supplied myself and other observers with specimens of this deposit for examination, that the fossils above described are now familiar to the British microscopists.

found, and a tri-radiate spiculum of a sponge.* Dr. Bailey has also observed two kinds of living Gaillonellæ, which are identical with fossil species. Hence it appears, that in the northern seas of the present day, there exist minute animals precisely similar to those which lived in a much lower latitude, at some very remote period.

The prevalence of marine and fresh-water animalcules in the same deposit is not unusual; and the remarks of Dr. Bailey on this subject are so just and pertinent, that I am induced to insert them, as a salutary caution against hasty generalizations. Dr. Bailey, after describing a species of Gaillonella ·(G. moniliformis), as an inhabitant only of salt and brackish water, and stating that he had also found it sixty miles up the Hudson River, near West Point, observes-" The Fauna and Flora of the Hudson at this place would, if in a fossil state, be rather puzzling to the geologist, on account of the singular mixture of marine and fluviatile species. While Valisneria and Potamogeton (two common fresh-water plants), grow in such vast quantities, in some places, as to prevent the passage of a boat; and the shore is strewn with fluviatile shells (such as Planorbis, Physa, &c.) in a living state; yet we find the above plants entangled with Alga (sea

* Microscopical Journal, Plate XV. contains figures of these objects.