barrier against the waves. An enormous amount of airborne dust is distributed over wide areas to form the loess soils of China or eastern Washington. Amethyst Mountain in Yellowstone Park shows at least seventeen forests, one above the other buried in volcanic dust. The sand particles carried by the wind are carving the cliffs into fantastic forms.

The distribution of the land and water areas presents some interesting problems. The present positions of the oceans and continents have been more or less permanent throughout all the time which geologists can measure. Yet there is evidence that shallow seas were once far more numerous than to-day. It is known that the specific gravity of the earth beneath the oceans is much greater than that of the continents. Barrell believes

that the ocean basins have been formed by the subsidence of broad areas of the crust, owing to the weight of magmas of high specific gravity rising widely and in enormous volume from a deep core of greater density into those portions of an originally lighter crust. This regional subsidence was especially characteristic of primordial times, but the process did not wholly cease then; since certain lines of evidence suggest that some ocean basins have been extended in later geologic ages, breaking into once wider continental platforms. The resultant increase in the volume of the ocean basins has led to a drawing off of the ocean waters from the continental areas, and a marked diminution of the shallow seas of earlier ages.1

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That the weight of the lava (magma) accumulating on a given area may be "enormous" may be seen by glancing at the vast lava field, covering between 200,000 and 300,000 square miles in Washington, California, Idaho, and Oregon, which is over 5,000 feet thick, having been put down in layers averaging about 75 feet.

It is well known that many of our mountain ranges were once seashores. I have seen clam shells on some of the

mountains of Haiti as thickly packed together as on any beach. The shrinking of the earth, together with the deposition of enormous weights of magma, seems to have produced from time to time those titanic convulsions which have thrown up the mountain ranges. The difference in the elevation of the earth's surface starts the waters flowing and causes the phenomena of erosion.

From the foot of the glacier comes a milky stream colored by sediment from the rocks ground to powder by the ice. From the hills the streams are carrying vast quantities of dirt to be deposited in the lowlands or carried to the ocean. Thus the Mississippi has built a delta of over 60,000 square miles extending practically from its old mouth at Cairo, Illinois to the Gulf where it is now depositing some 113,000,000 tons of silt yearly and extending its delta at the rate of a mile in sixteen years. This delta is so thick that driftwood has been found in a boring 1,042 feet deep at New Orleans. The entire land surface of the United States is being lowered at the rate of an inch in 760 years. All over the earth the same thing is happening. Slow as the rate may seem, the total amount carried to sea from the United States yearly is 270,000,000 tons of dissolved matter and 513,000,000 in suspension. Between one and two miles of igneous rock have been eroded from the surface of the earth, more than half of this having taken place before the Paleozoic era. The Rhone River has added a mile to its delta since Roman times. The town of Pu-tai in China, said to have been a third of a mile from the sea in the year 220 B.C., is now 48 miles from the shore. Some ocean shores are sinking, others rising. Erosion has taken some 3.5 miles from the top of the Uintah Mountains in Utah. Earthquake and volcano show that the earth is far from finished. "Even though the earth has been dissipating its inherited and derived energy for at least some hundred millions of years, and in so doing repeatedly given birth to

a new series of mountains, our mundane sphere is still far from having attained that internal stability that will, when achieved, result in a featureless earth, an atmosphere devoid of the carbon dioxide that is the basis of life, and a universal lifeless ocean-the facial expression which the earth will have in its old age.'

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Originally all the water on earth was fresh; now, as every one knows, the oceans and some lakes are salt. Throughout the ages the waters have been dissolving various salts out of the earth and carrying them to the oceans. Some of these have been deposited in great beds to be the supply of present generations, like that of Stassfurt in Germany which is 4,794 feet thick. Enormous deposits are reported from the Dead Sea of Palestine. Salty as the water of the ocean seems, it contains only 2.7 pounds per hundredweight. To have taken this amount of salt from the land and transferred it to the ocean has required from one to two hundred million years. Great Salt Lake in Utah is but the salty remnant of the vast fresh-water Lake Bonneville whose waters once flowed north through the Bear River, which now empties into the lake, and the Snake to the Pacific. This lake now contains 18 per cent of salt and a person cannot sink in it. Other lakes in arid regions have deposited most of the common salt (NaCl) and the liquid remaining is chiefly Epsom and Glauber salts. A similar fate awaits the oceans.

In the table of the chemical elements on page 8 no mention was made of such valuable substances as gold, silver, and platinum, while the much commoner metal copper appears at the foot of the list. Relatively they are very scarce, yet, as every one knows, they are sometimes found in considerable amounts. How does it happen? The explanation seems to be that they have been deposited in favored spots by the waters which constantly circulate in the earth. Water is a splendid solvent, assisted at times by other substances. There is a circulation of the water in the soil com

parable to the circulation of the air. No one knows how deeply into the earth it penetrates. Coming in contact with all the different elements, it has collected them and deposited them, possibly bringing many of them nearer the surface. Add to this the subsequent elevation of the mountain ranges and the later erosion by ice and water and we get a glimpse of the process. This explains the presence of minute quantities of gold in the oceans as well.

It may be broadly stated that were it not for the circulation of water with vast depths of the earth's crust we would have no workable deposits of any of the metals such as iron, copper, lead, tin, chromium, gold, platinum, or even of lime, phosphates, or petroleum. These materials with the exception of petroleum were originally contained in the molten magma of the earth and in the igneous rocks resulting from the cooling of the same. Most of them are present in only small proportions and are only very slightly soluble in water. For instance lead is contained in igneous rocks to the extent of .004 per cent, zinc .009 per cent, and copper .006 per cent. They are present in ordinary soil to about the same extent. Through various processes of chemical solutions and reactions and differences in solubilities of the various compounds they form, these metals have been completely separated from each other, carried up to or near the surface of the earth where, under other conditions, of which we know little or nothing, they have been deposited in workable beds often of immense proportions at different places on the earth's surface At other points on the earth's surface conditions are favorable for their precipitation and they wander up and down with the circulating waters in an unending search for a resting place. What a vast amount of water must have been used for their transportation to the surface and how complex must the process of separation and final segregation have been.14

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This process produces results both good and bad from the standpoint of man. The leaching of soluble salts from the ground in countries of good rainfall would mean that in time the elements necessary for plant food would be carried away and the land rendered sterile. Of the 272

pounds mentioned above as taken from each acre about 5.79 are potash and 0.54 pounds phosphoric acid. Yet there is abundant evidence that many old soils are fertile. The only answer must be that new supplies are brought in by the earth water. This is fortunate for man. In countries of poor rainfall many salts distinctly injurious to plant growth -calcium, magnesium, sodium-are brought to the surface and deposited as alkalies. There is plenty of evidence of this in the territory between the Rocky Mountains and the Sierras.

Let us restate briefly what is now known of the earth.

Taking all known facts into consideration . . . the best opinion is that the earth has a skin of ordinary earth and rock about 60 kilometers (37 miles) thick, then a shell 1,600 kilometers (954 miles) thick of compounds of iron, magnesium, and silicon, then a shell 1,400 kilometers (37 miles) thick in which iron begins to predominate, and finally a nickel-iron core something like a meteorite in make-up 6,800 kilometers (4,225 miles) in diameter. The pressure at the center is something like 50,000,000 pounds per square inch, and the material there is about 10 times as heavy as water. Of course, other substances like platinum, gold, silver, lead, copper, are scattered through the mass, but it is not supposed that they make up a very large portion of the central core as compared to nickel-iron. This view is taken partly on account of the well known composition of meteorites.

So much for the size, weight and structure of the earth. Now a few words about its indispensable coverings, air and water. About 70 per cent of the earth's surface is submerged in water, and to an average depth of 12,000 feet. The atmosphere stretches up and up, getting rarer and rarer, till at 15 miles above the earth's surface 24/25 of it are left below. Yet there is air sufficient to produce white heat in meteors, as they rush into it, as high up as 100 miles. At the earth's equator, the air is composed in percentage by volume roughly as follows: