It will be useless to push these arguments further. The catastrophes which have produced the secondary strata, and the diluvian depositions, could not have been local or partial phenomena; but rather than call upon a comet, with the abstracted philosopher, to deluge the earth for every new geological epoch--or to change the axis of motion of our planet--or to resort to any of his wild, fanciful, and impious theories, we should, with Sir Humphrey Davy, even prefer the dream that all the secondary strata were _created_, filled with the remains, as it were, of animal life, to confound the speculations of our geological reasoners. ACKNOWLEDGMENTS. Every author who attempts a Monograph of any of the departments of Natural History, must necessarily depend, in a greater or less degree, upon the kindness and liberality of others. Rare and unique specimens, particularly of fossil species, are often scattered through different cabinets, and his work would be rendered very imperfect, if they were not intrusted to his care. In preparing the following Monograph on the plan of giving exact models of the species, instead of illustrating them by engravings in the usual manner, the specimens when used by the artist are perhaps more liable to accident, and it was at first supposed that this circumstance might have prevented the original design. But in no instance, where an application has been made, either to a public institution or to a private cabinet, has the author met with a refusal; indeed the courtesy, kindness, and liberality which he has experienced from naturalists, who have every where aided him in the prosecution of his work, form no inconsiderable portion of the gratification which he has received. Besides the acknowledgments to public museums, and to individuals, which are made in the body of the work, the author is desirous of recording in this place, the following cabinets from which he has derived much assistance. IN PHILADELPHIA. The Cabinet of John P. Wetherill. The Cabinet of the Academy of Natural Sciences. The Philadelphia Museum. (Peale's.) The Cabinet of P. A. Browne, Esq. The Cabinet of Dr. R. Harlan. The Cabinet of William Hyde. The Cabinet of J. Pierce. The Cabinet of the Geological Society. ———— Lambdin's Museum, Pittsburgh, Pa. The Cabinet of D. Keim, Reading, Pa. IN NEW YORK. The Cabinet of the Lyceum of Natural History. The Cabinet of Dr. J. E. Dekay. The New York Museum. (Peale's.) IN ALBANY.