Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/291

 Rh of the ancient seas, than are assigned to their few living representatives in our modern oceans.

It results from the view we have taken of the zoological affinities between living and extinct species of chambered shells, that they are all connected by one plan and organization; each forming a link-in the common chain, which unites existing species with those that prevailed among the earliest conditions of life upon our globe; and all attesting the Identity of the design, that has affected so many similar ends through such a variety of instruments, the principle of whose construction is, in every species, fundamentally the same.

Throughout the various living and extinct genera of Chambered shells, the use of the air-chambers and siphon, to adjust the specific gravity of the animals in rising and sinking, appears to have been identical. The addition of a new transverse plate within the conical shell added a new air-chamber, larger than the preceding one, to counterbalance the increase of weight that attended the growth of the shell and body of all these animals.

These beautiful arrangements are, and ever have been, subservient to a common object, viz. the construction of hydraulic instruments of essential importance in the economy of creatures destined to move sometimes at the bottom, and at other times upon or near the surface of the sea. The delicate adjustments whereby the same principle is extended through so many grades and modifications of a single type, show the uniform and constant agency of some controlling Intelligence; and in searching for the origin of so much method and regularity amidst variety, the mind can only rest, when it has passed back, through the subordinate series of Second causes, to that great First Cause, which is found in the will and power of a common Creator.