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62 DESIGN IN NATURE<br />
PLATE XL<br />
Plate x]. illustrates in a striking manner well-marked resemblances in inorganic and organic structures as<br />
regards longitudinal cleavage and transverse cleavage or segmentation.<br />
Fig. J.— Photograph of Fingal's Cave, Staffa, in the west of Soothxnd. Consists of vertical basaltic columns largely hexagonal in<br />
shape. They ave separated transversely at short intervals as in a vertebral column.<br />
Fig. 2.— Photiigraph of portion of the Giant's CaiLseway in the north of Ireland. The columns resemble those found in Fingal's<br />
Cave (Fig. 1 of this Plate). Figs. 1 and 2 of this Plate show the longitudinal and transverse cleavages in Plutonic rooks to perfection.<br />
Similar cleavages are seen in hydrated starch (I'^ig. .3 of this Plate). They greatly resemble the cleavages observed in plants and<br />
animals, especially the latter (Figs. .5, 6, 7, and 8 of this Plate), and point to a law of development or differentiation common to the<br />
inorganic and organic kingdoms (the Author).<br />
Fig. 3.— Pentagonal and hexagonal prismatic columns resembling those found in Fingal's Cave and the Giant's Causeway,<br />
produced artificially by evaporating and desiccating a fluid mixture of starch (the Author).<br />
Fiu. 4.—Fossil coral (Lithostrotion hasaltifonne) found in England, Ireland, Russia, Io«-a, and westward of the Mississippi<br />
(D. D. Owen). Shows beautiful prismatic, hexagonal columns, wonderfully reseiriljliug the basaltic rock columns found in Fingal's Cave<br />
and Giant's Causeway (Figs. 1 and 2 of this Plate), which I have shown can be produced artificially (Pig. 3 of this Plate).<br />
Fig. 5.—Fin or wing of the sturgeon (Acipeiiser), (after Giinther). Displays well-marked longitudinal cleavage with a certain<br />
amount of transverse cleavage, c, e, d, Root and thick, tapering semi-rigid margin of fin ; /, thin, elastic margin of fin. The<br />
triangular shape and graduated structure of the fin furnish the type for all propelling fins and wings—fins and wings having much<br />
in common, the latter being larger.<br />
Fig. 6.—Fore-limb of Ceratodus, a member of a family of very ancient fishes, dating back to the Triassic and Jurassic eras, and<br />
still surviving in Australian waters (after Giinther), Shows typical radiating, branching, segmented arrangements. The fore-limb<br />
forms a paddle rather than a fin or wing. It is not graduated, as in Fig. 5, to form a ]jropelIing organ. «, h, Root of fore-limb ;<br />
c, broad basal cartilage supporting tapering segmented axis and diverging rays ; d, tip of fore-limb ; e, anterior, and /, posterior<br />
margins of same.<br />
Fig. 7.—Trilobite (llomulonotus delphinocepludas), (after Nicholson). Shows transverse cleavage or segmentation.<br />
Fig. 8.—Human vertebral column or backbone (after Holden). Shows branching and typical transverse cleavage or segmentation.<br />
Compare with Fig. 7 of this Plate, and with the figures of Plate xxxix. The alternating curves presented by the backbone form a<br />
veritable line of beauty.<br />
Fig. 9.—A young coral {Luusdaleia flun'/ormix) with buds or corallites on the disc, illustrating calycular gemmation (M. Edwards).<br />
HEXAGONAL STRUCTURES<br />
In the United Kingdom and in almost every country in Europe igneous rocks occur. They do not necessarily<br />
form hills with cones and craters indicating their origin. Thus the rocks of Stafia in Scotland and the Giant's<br />
Causeway in Ireland are called basalt, and are known to be volcanic, as they agree in their columnar prismatic<br />
structure and mineral composition with the lava which has flowed from the craters of volcanoes. The remarkable<br />
structure of these rocks is supposed to be due to shrinkage and consohdation on coohng. Similar columnar pris-<br />
matic structures are produced when a mixture of hydrated starch is slowly dried off in the sun or in an oven. In<br />
both cases the columns, generally pentagonal or hexagonal in shape, are divided transversely at more or less<br />
regular intervals.^<br />
I direct attention to the basaltic prismatic columns as the longitudinal and transverse cleavages and hexagonal<br />
outline which they reveal re-appear in many living plant and animal structures. The longitudinal and transverse<br />
cleavages are seen in the Equisetacea), in cones and branches among plants, and in the segmented animals with limbs,<br />
bronchial tubes, &c. The hexagonal formations are witnessed in epithelial and liver cells, in scales and coverings,<br />
in transverse sections of fascicuh of muscle, in the enamel of teeth, in the honeycomb, in old-world corals, &c.<br />
A familar and striking example {Eunomia radiata) occurs in the coralline limestones. This is found in the Great<br />
OCihte, near Bath, where it is very conspicuous ; single individuals forming masses several feet in diameter, and<br />
which probably required centuries for their formation. Another good example (Favosites cervicornis) is met with<br />
in large numbers in the Devonian and Silurian groups, in the great limestones of Plymouth and Torbay. An<br />
' The I'ollowiug is the account given of these curious and interesting structures by Sir Charles Lyell : " One of the characteristic forms of<br />
voletuiic rocks, especially of ba.salt, is the colunuiar, whei-e large masses are divided into regular prisms, sometimes easily separable, but in other<br />
eases adhering firndy together. Tlie colunuis vary in the number of angles, from three to twelve ; but they have most commonly from five tn<br />
seven aides. They are often divided transversely, at nearly equal distances, like the joints in a vertebral column, as in the (Uant's Causeway in<br />
Ireland. Tliey vaiy exceedingly in resjject to length and diameter. Dr. MacCuUoch mentiims some in Skyc which are about 400 feet long ;<br />
othei's, in Morveu, not exceeding an inch. In regard to diameter, those of Ailsa measure 9 feet, and those of Morven an inch or less. They<br />
are usually straight, but sometimes curved ; and examples of both these occur in the island of Statfa. In a horizontal bed or sheet of trap the<br />
colunuis are vertical ;<br />
in a vertical dike they are horizontal."