Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/232

 228 have further evidence to show, that in times anterior to, and during the deposition of the Chalk, the same important functions were consigned to other carnivorous Mollusks, viz. the Testaceous Cephalopods; these are of comparatively rare occurrence in the Tertiary strata, and in our modern seas; but, throughout the Secondary and Transition formations, where carnivorous Trachelipods are either wholly wanting, or extremely scarce, we find abundant remains of carnivorous Cephalopods, consisting of the chambered shells of Nautili and Ammonites, and many kindred extinct genera of polythalamous shells of extraordinary beauty. The Molluscous inhabitants of all these chambered shells, probably possessed the voracious habits of the modern Cuttle Fish, and by feeding like them upon young Testacea and Crustacea, restricted the excessive increase of animal life at the bottom of the more ancient seas. Their sudden and nearly total disappearance at the commencement of the Tertiary era, would have caused a blank in the "police of nature," allowing the herbivorous tribes to increase to an excess, that would ultimately have been destructive of marine vegetation, as well as of themselves, had they not been replaced by a different order of carnivorous creatures, destined to perform in another manner, the office which the inhabitants of Ammonites and various extinct genera of chambered shells then ceased to discharge. From that time onwards, we have evidence of the abundance of carnivorous Trachelipods, and we see good reason to adopt the conclusion of Mr. Dillwyn, that "in the formations above the Chalk, the vast and sudden decrease of one predaceous tribe has been provided for by the creation of many new genera, and new species, possessed of similar appetencies, and yet formed for obtaining their prey by habits entirely different from those of the Cephalopods."