The shell of the ammonite is a continued arch, having transverse arches or ribs crossing the main arch, giving to _some_ particular forms of beauty, and to _all_ the peculiar symmetry of a series of spiral curves. But, to compensate for the thinness of the shell, a peculiar adaptation is provided; it consists in the flutings which are seen in the surface, occasioned by the transverse ribs. A pencil-case made of a thin plate of silver is all the stronger for being fluted, and the zinc roof of a railway station is fluted or corrugated, on the same principle. It is thus that strength is combined with economy of material and elegance of form. In the ammonite we see this recent invention anticipated by the Creator, long ages ere man had appeared. In addition to this, those round knobs or bosses studding some of the ammonites (_e.g._ 1 and 3), like gems upon a diadem, add strength as well as beauty to their frail forms, and thus served the same purpose as the groin work in gothic architecture, a beautiful illustration of which may be seen in the roof of Salisbury Cathedral. Then, looking at the chambers of the shell in the sections, we find that some were for living in, while others were mere empty air-cells, used for purposes of elevation or depression, according as the animal wished to rise to the top or sink to the bottom of the sea,—these front chambers being the drawing-rooms in which the aristocratic ammonite lived. Running _round_ them is an hydraulic instrument, called the siphuncle, or air-tube, by means of which singular mechanism this curious animal altered his specific gravity for purposes of sinking or swimming. “The universal prevalence of such delicate contrivances in the siphuncle, and of such undeviating and systematic union of buoyancy and strength in the air chambers throughout this entire family, are amongst the most prominent instances of order and method that pervade these remains of former races that inhabited the ancient seas; and strange indeed must be the construction of that mind, which can believe that all this order and method can have existed without the direction and agency of some commanding and controlling Mind,”[79] These are what Cowper finely calls “_the unambiguous footsteps of the God_;” and in tracing them our minds are elevated into exalted ideas of Him, whose wisdom is unsearchable, and whose ways are past finding out. With regard to the sections of the ammonite, as seen in the two previous figures, dimly indeed compared with the beautiful specimens from which they were copied, we can only add, in the words of the treatise just quoted, “Nothing can be more beautiful than the sinuous windings of these sutures in many species, at their union with the exterior shell, adorning it with a succession of most graceful forms, resembling festoons of foliage and elegant embroidery. When these thin septa are converted into iron pyrites, their edges appear like