Harper's Round Table, August 20, 1895 Part 6

"So do I. Wish you had said so before. Not that I mind exploring, but it's hot work such a day as this."

They found a shady bank and drew up under the bushes. Edith gave a sigh of relief.

"Do you mind if I smoke?" asked Bronson, getting out a silver cigarette-case with a _blase_ air.

"Oh, not at all."

"That's nice. Now we can be comfortable. I am so glad you came with me this afternoon, for I want to talk to you, Miss Franklin. I want in talk freely to you about something."

Edith's face expressed her astonishment.

"You look surprised," he continued, "but you will not be when I tell you what it is. You are the only person whom I can rely on to manage the matter well and to help me. It is connected with Neal Gordon."

[TO BE CONTINUED.]

AN EXPLANATION.

MAMMA. "Why do you come in every minute for something to eat, Herbert?"

HERBERT. "Because, mamma, I am so small that I cannot eat enough to last me over an hour."

ON THE EARTH AND IN THE SKY.

THE EARTH YESTERDAY, TO-DAY, TO-MORROW.

BY N. S. SHALER,

PROFESSOR OF GEOLOGY AT HARVARD UNIVERSITY.

From ancient days men have been seeking to learn the history of the earth; how it came to be set in the orderly array of the heavenly bodies; how it has step by step come forth from the ancient chaos to the existing perfection; how and to what end it is to go forward in ages beyond our own. In this century many thousands of able men have been engaged in these inquiries.

[Ill.u.s.tration: A RING THROWN FROM THE SUN FORMING A SEPARATE PLANET.]

The studies of astronomers have made it evident that in the olden days, indeed before days began, at a time which is to be reckoned as many hundred million years ago, the sun and the other bodies of the solar system, including our earth, the kindred planets and their satellites, were parts of a great ma.s.s of vapor or star dust, which extended throughout the s.p.a.ces in which these spheres now swing about the sun. As time went on this nebulous ma.s.s, just like many such ma.s.ses which the telescope reveals in the distant heavens, drew together, because its particles were impelled by gravitation towards the central point, and as it contracted it began to revolve, much as our earth and the other spheres as well now turn on their axes. Thus turning, it divided into successively formed rings, each of which in time broke up, the matter of the ring gathering into a separate planet. At first this planet, like the original ma.s.s, was gaslike, and when separated from the sun it began to gather in on itself, in most cases forming rings, which in time were to alter into the lesser spheres--the moons. The earth and all the planets lying further away from the sun have these little bodies about them, but in one case, as if to show the stages of creation, the unbroken ring remains, forming the magnificent circles which girdle Saturn. When, in the history of these wonderful processes of growth which have taken place in our solar system, our earth parted from the shrinking sun, the separate life of the sphere began. In the course of ages it set off the ma.s.s of the moon, and after that process was effected by further shrinking, it was reduced from a body several hundred thousand miles in diameter to a relatively small sphere. Such are the steps which led to the birth of our planet.

As the earth's matter gathered into a smaller bulk, its heat was greatly increased, so that for a time it was a hot, s.h.i.+ning star like the sun.

Gradually, however, it parted with so much of its heat that it, as we may say, froze over or became covered with a solid crust which soon became cool enough to permit the waters. .h.i.therto in the state of steam to descend upon the surface of the sphere. With this descent of the waters, which led to the formation of the seas, another stage of great importance in the history of the earth began. In the earlier ages the heat of the earth, which came from within its ma.s.s, was so great that the temperature coming from the sun was of no consequence, but when the earth acquired a crust of cold rocks, a new period began, that in which the solar heat was thereafter to be the source of most of the movements that occurred in this limited world. Thenceforward to the present day, and yet on through the ages, the sun and earth are linked together in their actions in a marvellously entangled way.

When the sun's heat began effectively to work on the earth in the manner which we now behold, the winds began to blow, the ocean waters under their influence to circulate currents, and the moisture to rise into the air to be carried to and fro and to fall as rain. It seems likely that these movements of air and water, which we know to be due to the action of the sun's heat, took place at first upon the surface which was everywhere covered by the ocean, a vast continuous sea through which the lands had not yet pierced, and in which living creatures had not begun to dwell. This universal field of waters could not have long continued, and this for the reason that certain changes in the earth itself brought about the creation of broad folds on the sea-bottom, which grew upward until dry lands rose above the level of the waters. The way in which this process took place can in general be easily understood.

After the earth had cooled to the point where its outer parts were what we term cold, and the whole of its ma.s.s approximately solid, it remained as it does to-day, exceedingly hot in its central portions, and therefore kept on slowly cooling. What we call the outer or crust part, because it had already become cool, had little heat to lose. The greater portion of the temperature, which crept away into the frigid places of the heavens, where the thermometer is always some hundred degrees below the freezing-point, came from the interior of the sphere. Because of this cooling in the deeper parts of the earth the ma.s.s shrunk in its interior portion, while the outer part, losing less heat, because it had less to lose, did not contract to anything like the same extent. Thus it came about that this crust portion which forms the surface, and that which is below to the depth of many miles, were forced to wrinkle in order to fit the diminished centre. The action may be compared, in a way, to what takes place when in an apple or other similar fruit or vegetable with a distinct skin the water dries out of the interior parts. The skin wrinkles, because it has little water to lose. Let us conceive that the heat which keeps the particles of matter apart in our earth answers to the water which separates the solid portions of the fruit, and the likeness becomes clear.

When the great wrinkles of the earth's crust were high enough to bring their surfaces in part above the level of the ocean, another important stage in the history of the sphere was begun. Before that time, the water which the sun's heat had lifted into the air, and sent back to the earth in the form of rain, had fallen into the ocean whence it came without in any way affecting the solid parts of the crust. But now a portion of it came down on what we call the dry land, making the beginning of the rivers and the lakes, and in its course to the sea wearing away the rocks over which it flowed, conveying the debris to the oceans, where it served to build layers of rocks upon the bottom, which with the further upward growth of the continent might in turn rise above the sea. Thus we may fairly reckon the appearance of the land above the seas as the third great event in the history of the earth.

After the earth had cooled down so that the waters had something like their present temperature, and probably after the lands had appeared, came the fourth and, on many accounts, the most interesting episode in the history of the planet. This was the beginning of what we call life, those little temporary gatherings of the earth's substance which take shape in the form of animals and plants. As yet we do not know, we are not likely indeed ever to know, just when or how this change from the earlier stage in which the earth knew no living creatures to that in which they were to abound in seas and on land. All that has been found out concerning the matter leads us to believe that the first steps led to the creation of very simple species--jellylike forms having but few of the qualities which we commonly a.s.sociate with living beings. But the first steps taken in the immemorable ages, the others followed in quick succession, so that the earliest fossil remains which we find in rocks formed on the sea-bottom, a hundred million or more years ago, show that the earth was richly peopled with a lowly life.

Probably at some time after the lands had risen above the sea, and had begun to yield their waste in the form of mud, sand, and pebbles, to provide strata on the sea-bottoms, volcanoes began to break forth on the sea-bottom and along the margins of the continents. These strange outbursts, mainly of steam, but often accompanied by molten rock, appear to owe their formation to the acc.u.mulation of beds on the bottom of the ocean, which as they are formed are to a great extent filled with water.

Acc.u.mulated to a thickness of many miles, the water in the lower part of these strata gradually becomes exceedingly heated. In the end it breaks forth in steam, having a temperature quite as hot as molten iron, so that it may melt ordinary rocks.

The beginning of volcanic action on the earth was in a way important, though the event is less noteworthy than any of those which have been previously remarked, for tremendous as a volcanic eruption may be (that of Kratakoa in 1883 shook a large part of the earth's surface, perturbed all its atmosphere, and sent its dust to every part of the world), they, after all, are not leading features in the earth's history, but rather incidents. It is otherwise with the last great physical event in the history of the earth, which we shall now have to consider.

As the earth became divided, so that there were a number of continents and oceans, its climate became diversified. This was in part accomplished by the changes in the course of the ocean currents, such as our Gulf Stream; in part it may have been by slight variation in the sun's heat. However brought about, from very ancient days to the present time large portions of the earth's surface have occasionally had climatal conditions which cause the rainfall to descend in the form of snow, the snow falling in such quant.i.ties that it did not melt away in the summer season. This condition now exists about either pole, and to a certain extent on the high mountains, even those of tropical lands.

From time to time, owing to the variable adjustments of climate, these periods of excessive snow have endured for ages, in which the glacial sheet has extended in either hemisphere far towards the equator. In our present day the earth is just escaping from the last of these wonderful ice epochs. At a time so recent that it may be called a geological yesterday the greater part of Europe and of North America was buried beneath acc.u.mulations of snow, or rather of ice formed from it, the sheets having in places the depth of a mile or more, and, according to their strange nature, moving slowly over the surface, crus.h.i.+ng and grinding the rocks as they went, until the ice either reached the sea, where it would float off as icebergs, or a place on the land where it was far enough south to be melted away.

[Ill.u.s.tration: THE ICE SHEET WAS DEEP ENOUGH TO FLOW OVER THE TOP OF MOUNT WAs.h.i.+NGTON.]

On the surface of North America the ice sheet, the remnant of which still covers Greenland, expelled all life from the region of Canada and the United States from a line a little to the east of the Rocky Mountains, and in general north of the Ohio and the Mississippi rivers to the sea-coast. It was deep enough to flow over the top of Mount Was.h.i.+ngton in New Hamps.h.i.+re, and a primitive man (for there were such in those days) might possibly have journeyed over all the realm without discerning the least trace of the earth's rock surface, for even the higher mountains were buried.

We do not yet know how many of these glacial periods there have been, or whether they occur at the same time in both the northern and southern hemispheres, but it is clear that they have been of frequent occurrence.

In the intervals between the ice epochs warm conditions appear to have prevailed even up to the pole of the hemisphere, which was shortly afterwards to experience the dreadful winter of an ice-time. Thus, at a period which in its geological sense was not long before the last glacial epoch, the Greenland district bore a forest much like that which now exists in parts of the Southern States of this country. It seems probable from the history of the past that the next revolution in our northern hemisphere will dissipate the ice about the arctic pole, and make a wide realm now uninhabitable to man fit for his use.

The foregoing little sketch of a few of the great events of the earth's history does not take into account the greatest of them all, the coming of man. But the conditions which surround the appearance of this flower of the earth are as yet so imperfectly known that they cannot well be considered.

HINTS TO YOUNG BOTANISTS.

BY CAROLINE A. CREEVY.

ROOTS.

When we are about to do a thing thoroughly and systematically we often say we will "begin at the root of the matter." That is because the root of a plant is supposed to be the first thing in its life. It is indeed the foundation, the substructure of a plant, but not strictly the first thing that starts to grow. The little stem feels the first quiver of life, and the root follows. You can see the little stem, or _caulicle_ in fat seeds like squash and melon, beans and pease. Split a squash seed, and between the two fat sides the caulicle lies cozily tucked, like a tiny tail or handle. Plant a squash seed in the earth. The caulicle, fed by the two fat sides, pushes its way upward into the air, making a stem with leaves, and finally a big vine, while from its lower end the root develops and pushes itself as fast as possible into the earth.

The roots of some plants are small. I think most weeds make pretty large and strong roots, which are hard to pull up. But when a tree has grown to its full size its roots are almost as large as its branches. I once saw a fine old maple-tree cut down, and its roots dug up to make room for a cellar. I was surprised to see what a big hole the roots made. Two men dug for several days before they had the roots all up.

The work for the roots to do is to drink water. The upper half of the plant is very thirsty, and calls constantly for water. The roots push and dig into the moist soil, drink in water, and pa.s.s it up by a sort of pumping process. Only think, drinking and pumping! That is what roots do. And so if the earth is dry, and the roots can find nothing to drink, the plant will die. But after a shower see how glad the leaves seem, and how stiff and straight they stand, because the roots are sucking up great draughts of water.

To protect roots in their hard burrowing work a little cap of hard cells is fitted over their tips. Little hairs grow all over them, whose purpose is to help absorb moisture.

Some thick and fleshy roots are good to eat. They form many of our best vegetables. Beets, turnips, parsnips, and carrots are such roots. They belong to biennial or two-year plants. The first year they store up food in their roots; the second year draw upon this food, and produce flowers and fruit. They are named from their shapes. _Fusiform_, like radishes, when thicker in the middle, tapering at both ends. Carrots are _conical_, thicker at the top. Turnips bulge out in the middle, and are _napiform_. When cl.u.s.tered like a dahlia the roots are _fascicled_. All are _taproots_, or main roots. Besides these _primary_ roots there are _secondary_. You may have noticed secondary roots springing from the joints of a corn-stalk above ground. The wonderful banyan-tree sends down roots from its branches, making new trees, until one tree is the mother of a colony.

There are plants which take their nourishment from the air alone, and not from the soil. They need roots as hold-fasts, not as drinking-cups.

Some lovely orchids grow in that way. Those leathery patches which you have seen on old fence-rails and rocks are lichens. They have roots for attachment only, and such are called _aerial_ roots.

Then there are _climbing_ rootlets. Look at the poison-ivy, but do not touch it, and you will see it climbing over tree-trunks and fence-posts by means of rootlets. The trumpet-creeper will show you the same thing.

These rootlets are very strong, as you will find if you try to pull, as I did once, a trumpet-creeper out of a grape-vine.