Chapter IV: Front Matter (4)

Agreeing with this statement as a whole, I nevertheless cannot but think it probable that a great deal of the asphalt, whether it be in large masses or in scattered veins, may be moving very slowly down hill, from the lake to the sea, by the process of expansion by day and contraction by night, and may be likened to a caterpillar, or rather caterpillars innumerable, progressing by expanding and contracting their rings, having strength enough to crawl down hill, but not strength enough to back up hill again.

At last we surmounted the last rise, and before us lay the famous lake--not at the bottom of a depression, as we expected, but at the top of a rise, whence the ground slopes away from it on two sides, and rises from it very slightly on the two others. The black pool glared and glittered in the sun. A group of islands, some twenty yards wide, were scattered about the middle of it. Beyond it rose a double forest of Moriche fan-palms; and to the right of them high wood with giant Mombins and undergrowth of Cocorite--a paradise on the other side of the Stygian pool.

We walked, with some misgivings, on to the asphalt, and found it perfectly hard. In a few steps we were stopped by a channel of clear water, with tiny fish and water-beetles in it; and, looking round, saw that the whole lake was intersected with channels, so unlike anything which can be seen elsewhere that it is not easy to describe them.

Conceive a crowd of mushrooms, of all shapes, from ten to fifty feet across, close together side by side, their tops being kept at exactly the same level, their rounded rims squeezed tight against each other; then conceive water poured on them so as to fill the parting seams, and in the wet season, during which we visited it, to overflow the tops somewhat. Thus would each mushroom represent, tolerably well, one of the innumerable flat asphalt bosses, which seem to have sprung up each from a separate centre, while the parting seams would be of much the same shape as those in the asphalt, broad and shallow atop, and rolling downward in a smooth curve, till they are at bottom mere cracks from two to ten feet deep. Whether these cracks actually close up below, and the two contiguous masses of pitch become one, cannot be seen. As far as the eye goes down, they are two, though pressed close to each other. Messrs. Wall and Sawkins explain the odd fact clearly and simply. The oil, they say, which the asphalt contains when it rises first, evaporates in the sun, of course most on the outside of the heap, leaving a thorough coat of asphalt, which has, generally, no power to unite with the corresponding coat of the next mass. Meanwhile Mr. Manross, an American gentleman, who has written a very clever and interesting account of the lake, seems to have been so far deceived by the curved and squeezed edges of these masses that he attributes to each of them a revolving motion, and supposes that the material is continually passing from the centre to the edges, when it "rolls under," and rises again in the middle. Certainly the strange stuff looks, at the first glance, as if it were behaving in this way; and certainly, also, his theory would explain the appearance of sticks and logs in the pitch. But Messrs. Wall and Sawkins say that they have observed no such motion: nor did we; and I agree with them, that it is not very obvious to what force, or what influence, it could be attributable. We must, therefore, seek some other way of accounting for the sticks--which utterly puzzled us, and which Mr. Manross well describes as "numerous pieces of wood, which, being involved in the pitch, are constantly coming to the surface. They are often several feet in length, and five or six inches in diameter. On reaching the surface they generally assume an upright position, one end being detained in the pitch, while the other is elevated by the lifting of the middle. They may be seen at frequent intervals over the lake, standing up to the height of two or even three feet. They look like stumps of trees protruding through the pitch; but their parvenu character is curiously betrayed by a ragged cap of pitch which invariably covers the top, and hangs down like hounds' ears on either side."

Whence do they come? Have they been blown on to the lake, or left behind by man? or are they fossil trees, integral parts of the vegetable stratum below which is continually rolling upward? or are they of both kinds? I do not know. Only this is certain, as Messrs. Wall and Sawkins have pointed out, that not only "the purer varieties of asphalt, such as approach or are identical with asphalt glance, have been observed" (though not, I think, in the lake itself) "in isolated masses, where there was little doubt of their proceeding from ligneous substances of larger dimensions, such as roots and pieces of trunks and branches," but, moreover, that "it is also necessary to admit a species of conversion by contact, since pieces of wood included accidentally in the asphalt, for example, by dropping from overhanging vegetation, are often found partially transformed into the material." This is a statement which we verified again and again, as we did the one which follows, namely, that the hollow bubbles which abound on the surface of the pitch "generally contain traces of the lighter portion of vegetation," and "are manifestly derived from leaves, etc., which are blown about the lake by the wind, and are covered with asphalt, and, as they become asphalt themselves, give off gases which form bubbles round them."

But how is it that those logs stand up out of the asphalt, with asphalt caps and hounds' ears (as Mr. Manross well phrases it) on the tops of them?

We pushed on across the lake, over the planks which the negroes laid down from island to island. Some, meanwhile, preferred a steeple-chase with water-jumps, after the fashion of the midshipmen on a certain second visit to the lake. How the negroes grinned delight and surprise at the vagaries of English lads--a species of animal altogether new to them; and how they grinned still more when certain staid and portly dignitaries caught the infection, and proved by more than one good leap that they too had been English school-boys--alas! long, long ago.

So, whether by bridging, leaping, or wading, we arrived at the little islands, and found them covered with a thick, low scrub; deep sedge, and among them Pinguins, like huge pine-apples without the apple; gray wild-pines, parasites on Matapalos, which, of course, have established themselves, like robbers and vagrants as they are, everywhere; a true holly, with box-like leaves; and a rare cocoa-plum, very like the holly in habit, which seems to be all but confined to these little patches of red earth, afloat on the pitch. Out of the scrub, when we were there, flew off two or three night-jars, very like our English species, save that they had white in the wings; and on the second visit one of the midshipmen, true to the English boy's bird's-nesting instinct, found one of their eggs, white-spotted, in a grass nest.

Passing these little islands, which are said (I know not how truly) to change their places and number, we came to the very fountains of Styx, to that part of the lake where the asphalt is still oozing up.

As the wind set toward us, we soon became aware of an evil smell--petroleum and sulphureted hydrogen at once--which gave some of us a headache. The pitch here is yellow and white with sulphur foam; so are the water-channels; and out of both water and pitch innumerable bubbles of gas arise, loathsome to the smell. We became aware that the pitch was soft under our feet. We left the impression of our boots; and if we had stood still awhile, we should soon have been ankle-deep. No doubt there are spots where, if a man stayed long enough, he would be slowly and horribly engulfed. "But," as Mr. Manross says truly, "in no place is it possible to form those bowl-like depressions round the observer described by former travellers." What we did see is that the fresh pitch oozes out at the lines of least resistance, namely, in the channels between the older and more hardened masses, usually at the upper ends of them, so that one may stand on pitch comparatively hard, and put one's hand into pitch quite liquid, which is flowing softly out, like some ugly fungoid growth, such as may be seen in old wine-cellars, into the water. One such pitch-fungus had grown several yards in length in the three weeks between our first and second visit; and on another, some of our party performed exactly the same feat as Mr. Manross.

"In one of the star-shaped pools of water, some five feet deep, a column of pitch had been forced perpendicularly up from the bottom. On reaching the surface of the water it had formed a sort of centre-table, about four feet in diameter, but without touching the sides of the pool. The stem was about a foot in diameter. I leaped out on this table, and found that it not only sustained my weight, but that the elasticity of the stem enabled me to rock it from side to side. Pieces torn from the edges of this table sank readily, showing that it had been raised by pressure, and not by its buoyancy."

True, though strange; but stranger still did it seem to us when we did at last what the negroes asked us, and dipped our hands into the liquid pitch, to find that it did not soil the fingers. The old proverb that one cannot touch pitch without being defiled happily does not stand true here, or the place would be intolerably loathsome. It can be scraped up, moulded into any shape you will, wound in a string (as was done by one of the midshipmen) round a stick, and carried off; but nothing is left on the hand save clean gray mud and water. It may be kneaded for an hour before the mud be sufficiently driven out of it to make it sticky. This very abundance of earthy matter it is which, while it keeps the pitch from soiling, makes it far less valuable than it would be were it pure.

It is easy to understand whence this earthy matter (twenty or thirty per cent) comes. Throughout the neighborhood the ground is full, to the depth of hundreds of feet, of coaly and asphaltic matter. Layers of sandstone or of shale containing this decayed vegetable alternate with layers which contain none; and if, as seems probable, the coaly matter is continually changing into asphalt and oil, and then working its way upward through every crack and pore, to escape from the enormous pressure of the superincumbent soil, it must needs carry up with it innumerable particles of the soils through which it passes.

In five minutes we had seen, handled, and smelt enough to satisfy us with this very odd and very nasty vagary of tropic nature; and as we did not wish to become faint and ill between the sulphureted hydrogen and the blaze of the sun reflected off the hot black pitch, we hurried on over the water-furrows, and through the sedge-beds to the farther shore--to find ourselves, in a single step, out of an Inferno into a Paradise.

A STALAGMITE CAVE

(FROM THE VOYAGE OF THE CHALLENGER.)

BY SIR C. WYVILLE THOMSON, KT., LL.D., ETC.

I think the Painter's Vale cave is the prettiest of the whole. The opening is not very large. It is an arch over a great mass of débris forming a steep slope into the cave, as if part of the roof of the vault had suddenly fallen in. At the foot of the bank of débris one can barely see in the dim light the deep clear water lying perfectly still and reflecting the roof and margin like a mirror. We clambered down the slope, and as the eye became more accustomed to the obscurity the lake stretched further back. There was a crazy little punt moored to the shore, and after lighting candles Captain Nares rowed the Governor back into the darkness, the candles throwing a dim light for a time--while the voices became more hollow and distant--upon the surface of the water and the vault of stalactite, and finally passing back as mere specks into the silence.

After landing the Governor on the opposite side, Captain Nares returned for me, and we rowed round the weird little lake. It was certainly very curious and beautiful; evidently a huge cavity out of which the calcareous sand had been washed or dissolved, and whose walls, still to a certain extent permeable, had been hardened and petrified by the constant percolation of water charged with carbonate of lime. From the roof innumerable stalactites, perfectly white, often several yards long and coming down to the delicacy of knitting-needles, hung in clusters; and wherever there was any continuous crack in the roof or wall, a graceful, soft-looking curtain of white stalactite fell, and often ended, much to our surprise. Deep in the water Stalagmites also rose up in pinnacles and fringes through the water, which was so exquisitely still and clear that it was something difficult to tell where the solid marble tracery ended, and its reflected image began. In this cave, which is a considerable distance from the sea, there is a slight change of level with the tide sufficient to keep the water perfectly pure. The mouth of the cave is overgrown with foliage, and every tree is draped and festooned with the fragrant _Jasminum gracile_, mingled not unfrequently with the "poison ivy" (_Rhus toxicodendron_). The Bermudians, especially the dark people, have a most exaggerated horror of this bush. They imagine that if one touch it or rub against it he becomes feverish, and is covered with an eruption. This is no doubt entirely mythical. The plant is very poisonous, but the perfume of the flower is rather agreeable, and we constantly plucked and smelt it without its producing any unpleasant effect. The tide was with us when we regained the Flats Bridge, and the galley shot down the rapid like an arrow, the beds of scarlet sponges and the great lazy trepangs showing perfectly clearly on the bottom at a fathom depth.

Every here and there throughout the islands there are groups of bodies of very peculiar form projecting from the surface of the limestone where it has been weathered. These have usually been regarded as fossil palmetto stumps, the roots of trees which have been overwhelmed with sand and whose organic matter has been entirely removed and replaced by carbonate of lime. Fig. 1 represents one of the most characteristic of these from a group on the side of the road in Boaz Island. It is a cylinder a foot in diameter and six inches or so high; the upper surface forms a shallow depression an inch deep surrounded by a raised border; the bottom of the cup is even, and pitted over with small depressions like the marks of rain-drops on sand; the walls of the cylinder seem to end a few inches below the surface of the limestone in a rounded boss, and all over this there are round markings or little cylindrical projections like the origins of rootlets. The object certainly appears to agree even in every detail with a fossil palm-root, and as the palmetto is abundant on the islands and is constantly liable to be destroyed by and ultimately enveloped in a mass of moving sand, it seemed almost unreasonable to question its being one. Still something about the look of these things made me doubt, with General Nelson, whether they were fossil palms, or indeed whether they were of organic origin at all; and after carefully examining and pondering over several groups of them, at Boaz Island, on the shore at Mount Langton, and elsewhere, I finally came to the conclusion that they were not fossils, but something totally different.

The form given in Fig. 1 is the most characteristic, and probably by far the most common; but very frequently one of a group of these, one which is evidently essentially the same as the rest and formed in the same way, has an oval or an irregular shape (Figs. 2, 3, and 4). In these we have the same raised border, the same scars on the outside, the same origins of root-like fibres, and the same pitting of the bottom of the shallow cup; but their form precludes the possibility of their being tree-roots. In some cases (Fig. 5), a group of so-called "palm-stems" is inclosed in a space surrounded by a ridge, and on examining it closely this outer ridge is found to show the same leaf-scars and traces of rootlets as the "palm-stems" themselves. In some cases very irregular honey-combed figures are produced which the examination of a long series of intermediate forms shows to belong to the same category (Fig. 6).

In the caves in the limestone, owing to a thread of water having found its way in a particular direction through the porous stone of the roof, a drop falls age after age on one spot on the cave-floor, accurately directed by the stalactite which it is all the time creating. The water contains a certain proportion of carbonate of lime, which is deposited as stalagmite as the water evaporates, and thus a ring-like crust is produced at a little distance from the spot where the drop falls. When a ring is once formed, it limits the spread of the drop, and determines the position of the wall bounding the little pool made by the drop. The floor of the cave gradually rises by the accumulation of sand and travertine, and with it rise the walls and floor of the cup by the deposit of successive layers of stalagmite produced by the drop percolating into the limestone of the floor which hardens it still further, but in this peculiar symmetrical way. From the floor and sides of the cup the water oozes into the softer limestone around and beneath; but, as in all these limestones, it does not ooze indiscriminately, but follows certain more free paths. These become soon lined and finally blocked with stalagmite, and it is these tubes and threads of stalagmite which afterwards in the pseudo-fossil represent the diverging rootlets.

Sometimes when two or more drops fall from stalactites close to one another the cups coalesce (Figs. 2, 3, and 4); sometimes one drop or two is more frequent than the other, and then we have the form shown in Figs. 3 and 4; sometimes many drops irregularly scattered form a large pool with its raised border, and a few drops more frequent and more constant than the rest grow their "palmetto stems" within its limit (Fig. 5); and sometimes a number of drops near one another make a curious regular pattern, with the partitions between the recesses quite straight (Fig. 6).

I have already referred to the rapid denudation which is going on in these islands, and to the extent to which they have been denuded within comparatively recent times. The floors of caves, from their being cemented into a nearly homogeneous mass by stalagmitic matter, are much harder than the ordinary porous blown limestone; and it seems that in many cases, after the rocks forming the walls and roof have been removed, disintegration has been at all events temporarily arrested by the floor. Where there is a flat surface of rock exposed anywhere on the island, it very generally bears traces of having been at one time the floor of a cave; and as the weather-wearing of the surface goes on, the old concretionary structures are gradually brought out again, the parts specially hardened by a localized slow infiltration of lime resist integration longest and project above the general surface. Often a surface of weathered rock is so studded with these symmetrical concretions, that it is hard to believe that one is not looking at the calcified stumps of a close-growing grove of palms.

THE BIG TREES OF CALIFORNIA

(FROM STUDIES SCIENTIFIC AND SOCIAL.)

BY ALFRED RUSSEL WALLACE.

In the popular accounts of these trees it is usual to dwell only on the dimensions of the very largest known specimens, and sometimes even to exaggerate these. Even the smaller full-grown trees, however, are of grand dimensions, varying from fourteen to eighteen feet in diameter, at six feet above the ground, and keeping nearly the same thickness for perhaps a hundred feet. In the south Calaveras grove, where there are more than a thousand trees, the exquisite beauty of the trunks is well displayed by the numerous specimens in perfect health and vigor. The bark of these trees, seen at a little distance, is of a bright orange brown tint, delicately mottled with darker shades, and with a curious silky or plush-like gloss, which gives them a richness of color far beyond that of any other conifer. The tree which was cut down soon after the first discovery of the species, the stump of which is now covered with a pavilion, is twenty-five feet in diameter at six feet above the ground, but this is without the thick bark, which would bring it to twenty-seven feet when alive. A considerable portion of this tree still lies where it fell, and at one hundred and thirty feet from the base I found it to be still twelve and a half feet in diameter (or fourteen feet with the bark), while at the extremity of the last piece remaining, two hundred and fifteen feet from its base, it is six feet in diameter, or at least seven feet with the bark. The height of this tree when it was cut down is not recorded, but as one of the living trees is more than three hundred and sixty feet high, it is probable that this giant was not much short of four hundred feet.

In the accompanying picture the dead tree in the centre is that from which the bark was stripped, which was erected in the Crystal Palace and unfortunately destroyed by fire. It is called the "Mother of the Forest." The two trees nearer the foreground are healthy, medium-sized trees, about fifteen feet diameter at six feet above the ground.

The huge decayed trunk called "Father of the Forest," which has fallen perhaps a century or more, exhibits the grandest dimensions of any known tree. By measuring its remains, and allowing for the probable thickness of the bark, it seems to have been about thirty-five feet diameter near the ground, at ninety feet up fifteen feet, and even at a height of two hundred and seventy feet, it was nine feet in diameter. It is within the hollow trunk of this tree that a man on horse-back can ride--both man and horse being rather small; but the dimensions undoubtedly show that it was considerably larger than the "Pavilion tree," and that it carried its huge dimensions to a greater altitude; and although this does not prove it to have been much taller, yet it was in all probability more than four hundred feet in height.

Very absurd statements are made to visitors as to the antiquity of these trees, three or four thousand years being usually given as their age. This is founded on the fact that while many of the large Sequoias are greatly damaged by fire, the large pines and firs around them are quite uninjured. As many of these pines are assumed to be near a thousand years old, the epoch of the "great fire" is supposed to be earlier still, and as the Sequoias have not outgrown the fire-scars in all that time, they are supposed to have then arrived at their full growth. But the simple explanation of these trees alone having suffered so much from fire is, that their bark is unusually thick, dry, soft, and fibrous, and it thus catches fire more easily and burns more readily and for a longer time than that of the other coniferæ. Forest fires occur continually, and the visible damage done to these trees has probably all occurred in the present century. Professor C.B. Bradley, of the University of California, has carefully counted the rings of annual growth on the stump of the "Pavilion tree," and found them to be twelve hundred and forty; and after considering all that has been alleged as to the uncertainty of this mode of estimating the age of a tree, he believes that in the climate of California, in the zone of altitude where these trees grow, the seasons of growth and repose are so strongly marked that the number of annual rings gives an accurate result.

Other points that have been studied by Professor Bradley are, the reason why there are so few young trees in the groves, and what is the cause of the destruction of the old trees. To take the last point first, these noble trees seem to be singularly free from disease or from decay due to old age. All the trees that have been cut down are solid to the heart, and none of the standing trees show any indications of natural decay. The only apparent cause for their overthrow is the wind, and by noting the direction of a large number of fallen trees it is found that the great majority of them lie more or less towards the south. This is not the direction of the prevalent winds, but many of the tallest trees lean towards the south, owing to the increased growth of their topmost branches towards the sun. They are then acted upon by violent gales, which loosen their roots, and whatever the direction of the wind that finally overthrows them, they fall in the direction of the over-balancing top weight. The young trees grow spiry and perfectly upright, but as soon as they overtop the surrounding trees and get the full influence of the sun and wind, the highest branches grow out laterally, killing those beneath their shade, and thus a dome-shaped top is produced. Taking into consideration the health and vigor of the largest trees, it seems probable that, under favorable conditions of shelter from violent winds, and from a number of trees around them of nearly equal height, big trees might be produced far surpassing in height and bulk any that have yet been discovered. It is to be hoped that if any such are found to exist in the extensive groves of these trees to the south of those which are alone accessible to tourists, the Californian Government will take steps to reserve a considerable tract containing them, for the instruction and delight of future generations.

The scarcity of young Sequoias strikes every visitor, the fact being that they are only to be found in certain favored spots. These are, either where the loose débris of leaves and branches which covers the ground has been cleared away by fire, or on the spots where trees have been uprooted. Here the young trees grow in abundance, and serve to replace those that fall. The explanation of this is, that during the long summer drought the loose surface débris is so dried up that the roots of the seedling Sequoias perish before they can penetrate the earth beneath. They require to germinate on the soil itself, and this they are enabled to do when the earth is turned up by the fall of a tree, or where a fire has cleared off the débris. They also flourish under the shade of the huge fallen trunks in hollow places, where moisture is preserved throughout the summer. Most of the other conifers of these forests, especially the pines, have much larger seeds than the Sequoias, and the store of nourishment in these more bulky seeds enables the young plants to tide over the first summer's drought. It is clear, therefore, that there are no indications of natural decay in these forest giants. In every stage of their growth they are vigorous and healthy, and they have nothing to fear except from the destroying hand of man.

Destruction from this cause is, however, rapidly diminishing both the giant Sequoia and its near ally the noble redwood (_Sequoia sempervirens_), a tree which is more beautiful in foliage and in some other respects more remarkable than its brother species, while there is reason to believe that under favorable conditions it reaches an equally phenomenal size. It once covered almost all the coast ranges of central and northern California, but has been long since cleared away in the vicinity of San Francisco, and greatly diminished elsewhere. A grove is preserved for the benefit of tourists near Santa Cruz, the largest tree being two hundred and ninety-six feet high, twenty-nine feet diameter at the ground and fifteen feet at six feet above it. One of these trees having a triple trunk is here figured from a photograph. Much larger trees, however, exist in the great forests of this tree in the northern part of the State; but these are rapidly being destroyed for the timber, which is so good and durable as to be in great demand. Hence Californians have a saying that the redwood is too good a tree to live. On the mountains a few miles east of the Bay of San Francisco, there are a number of patches of young redwoods, indicating where large trees have been felled, it being a peculiarity of this tree that it sends up vigorous young plants from the roots of old ones immediately around the base. Hence in the forests these trees often stand in groups arranged nearly in a circle, thus marking out the size of the huge trunks of their parents. It is from this quality that the tree has been named _sempervirens_, or ever flourishing. Dr. Gibbons, of Alameda, who has explored all the remains of the redwood forests in the neighborhood of Oakland, kindly took me to see the old burnt-out stump of the largest tree he had discovered. It is situated about fifteen hundred feet above the sea, and is thirty-four feet in diameter at the ground. This is as large as the very largest specimens of the _Sequoia gigantea_, but it may have spread out more at the base and have been somewhat smaller above, though this is not a special characteristic of the species.

WHAT IS EVOLUTION?

(FROM THE ATLANTIC MONTHLY, MARCH, '93.)

BY PROFESSOR E.S. HOLDEN.

I was once trying to tell a boy, a friend of mine, what the scientific men mean by the long word _Evolution_, and to give him some idea of the plan of the world. I wanted an illustration of something that had grown--evolved, developed--from small beginnings up through more and more complicated forms, till it had reached some very complete form. I could think of no better example than the railway by which we were sitting. The trains were running over the very track where a wagon-road had lately been, and before that a country cart-track, and before that a bridle-path, and before that again a mere trail for cattle. So I took the road for an example, and tried to show my boy how it had grown from little things by slow degrees according to laws; and if you like, I will try to tell it again.

Just as one can go further and further back, and always find a bird to be the parent of the egg, and an egg to be the parent of that bird, so in the history of this road of ours; we may go back and back into the past, always finding something earlier, which is the cause of the something later. The earth, the planets, and the sun were all a fiery mist long ago. And in that mist, and in what came before it, we may look for the origin of things as they are. But we must begin somewhere. Let us begin with the landscape as we see it now,--hills, valleys, streams, mountains, grass,--but with only a single tree.

We will not try to say how the tree came there. At least, we will not try just yet. When we are through with the story you can say just as well as I can.

Suppose, then, a single oak-tree stood just on that hillside thousands and thousands of years ago. Grass was growing everywhere, and flowers, too. The seeds came with the winds. Year after year the oak-tree bore its acorns, hundreds and hundreds of them, and they fell on the grass beneath and rolled down the smooth slopes, and sprouted as best they could,--most of them uselessly so far as producing trees were concerned,--but each one did its duty and furnished its green sprout, and died if it found no nourishment.

All the hundreds of acorns rolled down the slopes, Not one rolled up; and here was a _law_,--the law of gravitation,--in full activity. There were scores of other laws active, too; for evolution had gone a long way when we had an earth fit to be lived on, and hills in their present shape, and a tree bearing acorns that would reproduce their kind. But ever since the fiery mist this simple law of gravitation has been acting, binding the whole universe together, making a relationship between each clod and every other clod, and forcing every stone, every acorn, and every rain-drop to move down and not up.

Just as this law operates,--continuously, silently, inexorably,--so every other law makes itself felt in its own sphere. Gravitation is simple. The law according to which an acorn makes an oak--and not a pine-tree is complex. But the laws of Nature are all alike, and if we understand the simple ones, we can at least partly comprehend the more complex. They are nothing but fixed habits on a large scale.

So the acorns fell year by year and sprouted; and one out of a thousand found good soil, and was not wasted, and made a tree. And so all around (below) the tree with which we started there grew a grove of oaks like it, in fact its children; and finally the original trees died, but not without having left successors.

First of all, the green hillside is smooth and untrodden. There is nothing but grass and flowers, borne there by the winds, which leave no track. There is no animal life even in this secluded spot save the birds, and they too leave no track. By and by there comes a hard winter, or a dearth of food, and a pair of stray squirrels emigrate from their home in the valley below; and the history of our hill and its woods begins. Mere chance decides the choice of the particular oak-tree in which the squirrels make their home. From the foot of this tree they make excursions here and there for their store of winter food,--acorns and the like,--and they leave little paths on the hillside from tree to tree.

The best-marked paths run to the places where there are the most acorns. A little later on there are more squirrels in the colony,--the young of the parent pair, and other colonists from the valley. The little tracks become plainer and plainer.

Later still come other wild animals in search of food,--squirrels will do. The wild animals do not remain in the colony (there are too few squirrels, and they are too hard to catch), but they pass through it, sometimes by day but oftenest by night.

You might think it was perfectly a matter of chance along which path a bear or a wolf passed, but it was not. He _could_ walk anywhere on the hillside; and sometimes he would be found far out of the paths that the squirrels had begun. But usually, when he was in no haste, he took the easiest path. The easiest one was that which went between the bushes and not through them; along the hillside and not straight up it; around the big rocks and not over them. The wolves and bears and foxes have new and different wants when they come; and they break new paths to the springs where they drink, to the shade where they lie, to the hollow trees where the bees swarm and store the wild honey.

But the squirrels were the first surveyors of these tracks. The bears and wolves are the engineers, who change the early paths to suit their special convenience.

By and by the Indian hunter comes to follow the wild game. He, too, takes the easiest trail, the path of least resistance; and he follows the track to the spring that the deer have made, and he drinks there. He is an animal as they are, and he satisfies his animal wants according to the same law that governs them.

After generations of hunters, Indians, and then white men, there comes a man on horseback looking for a house to live in. He, too, follows along the easiest paths and stops at the spring; and near by he finds the place he is looking for. Soon he returns, driving before him herds of cattle and flocks of sheep, which spread over the grassy glades to feed. But everywhere they take the easiest place, the old paths, from the shady tree to the flowing spring. After awhile the hillside is plainly marked with these sheep trails. You can see them now whenever you go into the country, on every hillside.

Soon there are neighbors who build their homes in the next valley, and a good path must be made between the different houses.

A few days' work spent in moving the largest stones, in cutting down trees, and in levelling off a few steep slopes, makes a trail along which you can gallop your horse.

Things move fast now,--history begins to be made quickly as soon as man takes a hand in it. Soon the trail is not enough: it must be widened so that a wagon-load of boards for a new house can be carried in (for the settler has found a wife). After the first cart-track is made to carry the boards and shingles in, a better road will be needed to haul firewood and grain out (for the wants of the new family have increased, and things must be bought in the neighboring village with money, and money can only be had by selling the products of the farm). By and by the neighborhood is so well inhabited that it is to the advantage of the villages all around it to have good and safe and easy roads there; and the road is declared a public one, and it is regularly kept in repair and improved at the public expense. Do not forget the squirrels of long ago. They were the projectors of this road. Their successors use it now,--men and squirrels alike,--and stop at the spring to drink, and under the huge oaks to rest.

A few years more, and it becomes to the advantage of all to have a railway through the valley and over the hillside. Then a young surveyor, just graduated from college, comes with his chain-men and flag-men, and finds that the squirrels, and bears, and hunters, and all the rest have picked out the easiest way for him long centuries ago. He makes his map, and soon the chief enigneer and the president of the road drive along in a buggy with a pair of fast horses (frightening the little squirrels off their road-way and into their holes), and the route of the Bear Valley and Quercus Railway is finally selected, and here it is. See! there comes a train along the track. This is the way a railway route grew out of a squirrel path. There are thousands of little steps, but you can trace them, or imagine them, as well as I can tell you.

It is the same all over the world. Stanley cut a track through the endless African forests. But it lay between the Pygmy villages, along the paths they had made, and through the glades where they fought their battles with the storks.

Sometimes the first road is a river--the track is already cut. Try to find out where the settlements in America were in the very early days--before 1800. You will find them along the Hudson, the Juanita, the St. Lawrence, the James, the Mississippi Rivers. But when these are left, men follow the squirrel-tracks and bear-tracks, or the paths of hunters, or the roads of Roman soldiers. It is a standing puzzle to little children why all the great rivers flow past the great towns. (Why do they?) The answer to that question will tell you why the great battles are fought in the same regions; why Egypt has been the coveted prize of a dozen different conquerors (it is the gateway of the East); why our Civil War turned on the possession of the Mississippi River. It is the roadways we fight for, the ways in and out, whether they be land or water. Of course, we really fought for something better than the mere possession of a roadway, but to get what we fought for we had to have the roadway first.

The great principle at the bottom of everything in Nature is that the fittest survives: or, as I think it is better to say it, in any particular conflict or struggle that thing survives which is the fittest to survive _in this particular struggle_. This is Mr. Darwin's discovery,--or one of them,--and the struggle for existence is a part of the great struggle of the whole universe, and the laws of it make up the methods of Evolution--of Development.

It is clear now, is it not, how the railway route is the direct descendant of the tiny squirrel track between two oaks? The process of development we call Evolution, and you can trace it all around you. Why are your skates shaped in a certain way? Why is your gun rifled? Why have soldiers two sets of (now) useless buttons on the skirts of their coats? (I will give you three guesses for this, and the hint that you must think of cavalry soldiers.) Why are eagles' wings of just the size that they are? These and millions of like questions are to be answered by referring to the principle of development.

Sometimes it is hard to find the clew. Sometimes the development has gone so far, and the final product has become so complex and special, that it takes a good deal of thinking to find out the real reasons. But they _can_ be found, whether they relate to a fashion, to one of the laws of our country, or to the colors on a butterfly's wing.

There is a little piece of verse intended to be comic, which, on the contrary, is really serious and philosophical, if you understand it. Learn it by heart, and apply it to all kinds and conditions of things, and see if it does not help you to explain them to yourself....

"And Man grew a thumb for that he had need of it,
And developed capacities for prey.
For the fastest men caught the most animals,
And the fastest animals got away from the most men.
Whereby all the slow animals were eaten,
And all the slow men starved to death."

HOW THE SOIL IS MADE

(FROM THE FORMATION OF VEGETABLE MOULD.)

BY CHARLES DARWIN.

Worms have played a more important part in the history of the world than most persons would at first suppose. In almost all humid countries they are extraordinarily numerous, and for their size possess great muscular power. In many parts of England a weight of more than ten tons (10,516 kilogrammes) of dry earth annually passes through their bodies and is brought to the surface on each acre of land; so that the whole superficial bed of vegetable mould passes through their bodies in the course of every few years. From the collapsing of the old burrows the mould is in constant though slow movement, and the particles composing it are thus rubbed together. By these means fresh surfaces are continually exposed to the action of the carbonic acid in the soil, and of the humus-acids which appear to be still more efficient in the decomposition of rocks. The generation of the humus-acids is probably hastened during the digestion of the many half-decayed leaves which worms consume. Thus the particles of earth, forming the superficial mould, are subjected to conditions eminently favorable for their decomposition and disintegration. Moreover, the particles of the softer rocks suffer some amount of mechanical trituration in the muscular gizzards of worms, in which small stones serve as mill-stones.

The finely levigated castings, when brought to the surface in a moist condition, flow during rainy weather down any moderate slope; and the smaller particles are washed far down even a gently inclined surface. Castings when dry often crumble into small pellets and these are apt to roll down any sloping surface. Where the land is quite level and is covered with herbage, and where the climate is humid so that much dust cannot be blown away, it appears at first sight impossible that there should be any appreciable amount of sub-aerial denudation; but worm castings are blown, especially while moist and viscid, in one uniform direction by the prevalent winds which are accompanied by rain. By these several means the superficial mould is prevented from accumulating to a great thickness; and a thick bed of mould checks in many ways the disintegration of the underlying rocks and fragments of rock.

The removal of worm-castings by the above means leads to results which are far from insignificant. It has been shown that a layer of earth,.2 of an inch in thickness, is in many places annually brought to the surface per acre; and if a small part of this amount flows, or rolls, or is washed, even for a short distance, down every inclined surface, or is repeatedly blown in one direction, a great effect will be produced in the course of ages. It was found by measurements and calculations that on a surface with a mean inclination of 9° 26', 2.4 cubic inches of earth which had been ejected by worms crossed, in the course of a year, a horizontal line one yard in length; so that two hundred and forty cubic inches would cross a line one hundred yards in length. This latter amount in a damp state would weigh eleven and one-half pounds. Thus, a considerable weight of earth is continually moving down each side of every valley, and will in time reach its bed. Finally, this earth will be transported by the streams flowing in the valleys into the ocean, the great receptacle for all matter denuded from the land. It is known from the amount of sediment annually delivered into the sea by the Mississippi, that its enormous drainage-area must on an average be lowered.00263 of an inch each year; and this would suffice in four and a half million years to lower the whole drainage-area to the level of the seashore. So that if a small fraction of the layer of fine earth,.2 of an inch in thickness, which is annually brought to the surface by worms, is carried away, a great result cannot fail to be produced within a period which no geologist considers extremely long.

(Scale, 1/2 inch to 1 foot.)]

Archaeologists ought to be grateful to worms, as they protect and preserve for an indefinitely long period every object, not liable to decay, which is dropped on the surface of the land, by burying it beneath their castings. Thus, also, many elegant and curious tesselated pavements and other ancient remains have been preserved; though no doubt the worms have in these cases been largely aided by earth washed and blown from the adjoining land, especially when cultivated. The old tesselated pavements have, however, often suffered by having subsided unequally from being unequally undermined by the worms. Even old massive walls may be undermined and subside; and no building is in this respect safe, unless the foundations lie six or seven feet beneath the surface, at a depth at which worms cannot work. It is probable that many monoliths and some old walls have fallen down from having been undermined by worms.

Worms prepare the ground in an excellent manner for the growth of fibrous-rooted plants and for seedlings of all kinds. They periodically expose the mould to the air, and sift it so that no stones larger than the particles which they can swallow are left in it. They mingle the whole intimately together, like a gardener who prepares fine soil for his choicest plants. In this state it is well fitted to retain moisture and to absorb all soluble substances, as well as for the process of nitrification. The bones of dead animals, the harder parts of insects, the shells of land mollusks, leaves, twigs, etc., are before long all buried beneath the accumulated castings of worms, and are thus brought in a more or less decayed state within reach of the roots of plants. Worms likewise drag an infinite number of dead leaves and other parts of plants into their burrows, partly for the sake of plugging them up and partly as food.

The leaves which are dragged into the burrows as food, after being torn into the finest shreds, partially digested and saturated with the intestinal and urinary secretions, are commingled with much earth. This earth forms the dark-colored, rich humus which almost everywhere covers the surface of the land with a fairly well-defined layer or mantle. Von Hensen placed two worms in a vessel eighteen inches in diameter, which was filled with sand, on which fallen leaves were strewed; and these were soon dragged into their burrows to a depth of three inches. After about six weeks an almost uniform layer of sand, a centimetre (.4 inch) in thickness, was converted into humus by having passed through the alimentary canals of these two worms. It is believed by some persons that worm-burrows, which often penetrate the ground almost perpendicularly to a depth of five or six feet, materially aid in its drainage; notwithstanding that the viscid castings piled over the mouths of the burrows prevent or check the rain-water directly entering them. They allow the air to penetrate deeply into the ground. They also greatly facilitate the downward passage of roots of moderate size; and these will be nourished by the humus with which the burrows are lined. Many seeds owe their germination to having been covered by castings; and others buried to a considerable depth beneath accumulated castings lie dormant, until at some future time they are accidentally uncovered and germinate.

Worms are poorly provided with sense-organs, for they cannot be said to see, although they can just distinguish between light and darkness; they are completely deaf, and have only a feeble power of smell; the sense of touch alone is well developed. They can, therefore, learn little about the outside world, and it is surprising that they should exhibit some skill in lining their burrows with their castings and with leaves, and in the case of some species in piling up their castings into tower-like constructions. But it is far more surprising that they should apparently exhibit some degree of intelligence instead of a mere blind, instinctive impulse, in their manner of plugging up the mouths of their burrows. They act in nearly the same manner as would a man, who had to close a cylindrical tube with different kinds of leaves, petioles, triangles of paper, etc., for they commonly seize such objects by their pointed ends. But with thin objects a certain number are drawn in by their broader ends. They do not act in the same unvarying manner in all cases, as do most of the lower animals; for instance, they do not drag in leaves by their foot-stalks, unless the basil part of the blade is as narrow as the apex, or narrower than it.

* * * * *

When we behold a wide, turf-covered expanse, we should remember that its smoothness, on which so much of its beauty depends, is mainly due to all the inequalities having been slowly levelled by worms. It is a marvellous reflection that the whole of the superficial mould over any such expanse has passed, and will again pass, every few years through the bodies of worms. The plough is one of the most ancient and most valuable of man's inventions; but long before he existed the land was in fact regularly ploughed, and, still continues to be thus ploughed by earth-worms. It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organized creatures. Some other animals, however, still more lowly organized, namely, corals, have done far more conspicuous work in having constructed innumerable reefs and islands in the great oceans; but these are almost confined to the tropical zones.

ZOÖLOGICAL MYTHS

(FROM FACTS AND FICTIONS OF ZOÖLOGY.)

BY ANDREW WILSON.