Part 17

"The rate of growth of the common branching madrepore is not over one and a half inches a year. As the branches are open, this would not be equivalent to more than half an inch in height of solid coral for the whole surface covered by the madrepore; and, as they are also porous, to not over three-eighths of an inch of solid limestone. But a coral plantation has large bare patches without corals, and the coral sands are widely distributed by currents, part of them to depths over one hundred feet where there are no living corals; not more than one-sixth of the surface of a reef region is, in fact, covered with growing species. This reduces the three-eighths to ONE-SIXTEENTH. Shells and other organic relics may contribute one-fourth as much as corals. At the outside, the average upward increase of the whole reef-ground per year would not exceed ONE-EIGHTH of an inch.

"Now some reefs are at least two thousand feet thick, which at one-eighth of an inch a year, corresponds to one hundred and ninety-two thousand years."*

* Dana, Manual of Geology, p. 591.

Halve, or quarter, this estimate if you will, in order to be certain of erring upon the right side, and still there remains a prodigious period during which the ancestors of existing coral polypes have been undisturbedly at work; and during which, therefore, the climatal conditions over the coral area must have been much what they are now.

And all this lapse of time has occurred within the most recent period of the history of the earth. The remains of reefs formed by coral polypes of different kinds from those which exist now, enter largely into the composition of the limestones of the Jurassic period; and still more widely different coral polypes have contributed their quota to the vast thickness of the carboniferous and Devonian strata. Then as regards the latter group of rocks in America, the high authority already quoted tells us:--

"The Upper Helderberg period is eminently the coral reef period of the palaeozoic ages. Many of the rocks abound in coral, and are as truly coral reefs as the modern reefs of the Pacific. The corals are sometimes standing on the rocks in the position they had when growing: others are lying in fragments, as they were broken and heaped by the waves; and others were reduced to a compact limestone by the finer trituration before consolidation into rock. This compact variety is the most common kind among the coral reef rocks of the present seas; and it often contains but few distinct fossils, although formed in water that abounded in life. At the fall of the Ohio, near Louisville, there is a magnificent display of the old reef. Hemispherical Favosites, five or six feet in diameter, lie there nearly as perfect as when they were covered by their flowerlike polypes; and besides these, there are various branching corals, and a profusion of Cyathophyllia, or cup-corals."*

* Dana, Manual of Geology, p. 272.

Thus, in all the great periods of the earth's history of which we know anything, a part of the then living matter has had the form of polypes, competent to separate from the water of the sea the carbonate of lime necessary for their own skeletons. Grain by grain, and particle by particle, they have built up vast masses of rock, the thickness of which is measured by hundreds of feet, and their area by thousands of square miles. The slow oscillations of the crust of the earth, producing great changes in the distribution of land and water, have often obliged the living matter of the coral-builders to shift the locality of its operations; and, by variation and adaptation to these modifications of condition, its forms have as often changed. The work it has done in the past is, for the most part, swept away, but fragments remain, and, if there were no other evidence, suffice to prove the general constancy of the operations of Nature in this world, through periods of almost inconceivable duration.

NOTES

AUTOBIOGRAPHY

O, it came o'er my ear like the sweet sound That breathes upon a bank of violets, Stealing and giving odour.

For the reading "sweet south" instead of "sweet sound," see Rolfe's edition of Twelfth Night.]

Charing Cross School of Medicine: a school connected with the Charing Cross Hospital in the Strand, London.]

ON THE ADVISABLENESS OF IMPROVING NATURAL KNOWLEDGE (1866)

For the history of the times mentioned in this essay, see Green's Short History of the English People.]

When I was a beggarly boy, And lived in a cellar damp, I had not a friend or a toy, But I had Aladdin's lamp; When I could not sleep for the cold, I had fire enough in my brain, And builded, with roofs of gold, My beautiful castles in Spain!]

A LIBERAL EDUCATION (1868)

ON A PIECE OF CHALK

"'Wie das Gestirn, Ohne Hast, Ohne Rast'--

something may be done, and some of Sister Lizzie's fond imaginations turn out not altogether untrue." The quotation entire is as follows:--

Wie das Gestirn, Ohne Hast, Aber ohne Rast, Drehe sich jeder Um die eigne Last.]

THE PRINCIPAL SUBJECTS OF EDUCATION (1882)

THE METHOD OF SCIENTIFIC INVESTIGATION (1863)

ON THE PHYSICAL BASIS OF LIFE (1868)

As forests change their foliage year by year, Leaves, that come first, first fall and disappear; So antique words die out, and in their room, Others spring up, of vigorous growth and bloom; Ourselves and all that's ours, to death are due, And why should words not be mortal too?

Martin's translation.]

"The design of this work, as stated by Pope himself, is to ridicule all the false tastes in learning under the character of a man of capacity enough, that had dipped into every art and science, but injudiciously in each. It was begun by a club of some of the greatest wits of the age--Lord Oxford, the Bishop of Rochester, Pope, Congreve, Swift, Arbuthnot, and others. Gay often held the pen; and Addison liked it very well, and was not disinclined to come into it."]

"Thus there can be little doubt, that the further science advances, the more extensively and consistently will all the phaenomena of Nature be represented by materialistic formulae and symbols. But the man of science, who, forgetting the limits of philosophical inquiry, slides from these formulae and symbols into what is commonly understood by materialism, seems to me to place himself on a level with the mathematician, who should mistake the x's and y's with which he works his problems, for real entities--and with this further disadvantage, as compared with the mathematician, that the blunders of the latter are of no practical consequence, while the errors of systematic materialism may paralyze the energies and destroy the beauty of a life."]