point out the specific uses of each minute variation, in the arrangement of parts fundamentally the same.
The geographical distribution of Ammonites in the ancient world, seems to have partaken of that universality, we find so common in the animals and vegetables of a former condition of our globe, and which differs so remarkably from the varied distribution that prevails among existing forms of organic life. We find, the same genera, and, in a few cases, the same species of Ammonites, in strata, apparently of the same age, not only throughout Europe, but also in distant regions of Asia, and of North and South America.[1]
Hence we infer that during the Secondary and Transition periods a more general distribution of the same species, than exists at present, prevailed in regions of the world most remotely distant from one another.
An Ammonite, like a Nautilus, is composed of three essential parts: 1st. An external shell, usually of a fiat discoidal form, and having its surface strengthened and ornamented with ribs (see Pl. 35, and Pl. 37.) 2d. A series of internal air chambers formed by transversed plates, intersecting
- ↑ Dr. Gerard has discovered at the elevation of sixteen thousand feet in the Himmalaya Mountains, species of Ammonites, e. g. A. Walcoti, and A. Communis, identical with those of the Lias at Whitby and Lyme Regis. He has also found in the same parts of the Himmalaya, several species of Belemnite, with Terebutulæ, and other bivalves, that occur in the English Oolite; thereby establishing the existence of the Lias, and Oolite formations in that elevated and distant region of the world. He has also collected in the same Mountains, shells of the genera Spirifer, Products, and Terebratula, which occur in the Transition formations of Europe and America.
The Greensand of New Jersey also contains Ammonites mixed with Hamites and Scaphites, as in the green sand of England, and Captain Beechy and Lieutenant Belcher found Ammonites on the coast of Chili in Lat. 36 S. in the Cliffs near Conception; a fragment of one of these Ammonites is preserved in the Museum of Hasler Hospital at Gosport.
Mr. Sowerby possesses fossil shells from Brazil resembling those of the Inferior Oolite of England.
