Of all the Gault fossils, the Ammonites take precedence both for beauty and number; and, holding as the Cephalopods do the highest rank of molluscous animals, we cannot but view their extraordinary variety in this deposit with singular interest. If, therefore, we dwell here somewhat at length on their general classification, we could scarcely choose a more fitting occasion.

As ordinarily seen in collections, the Gault Ammonites appear to be all more or less of diminutive size. Few exceed two inches in diameter; many are little more than an inch; while one of three inches would be looked upon as a fine individual.

These specimens are, however, for the most part only the central whirls solidified or hardened by interior walls, or in-fillings of iron-pyrites. In the Gault itself Ammonite-shells of far larger size—commonly of six or seven inches across, sometimes more than a foot—are not merely frequent, but extremely abundant, although, from the fragile state of the main mass, they are commonly cleft to pieces in breaking out the central pyritous cores without attracting observation.