The water vapor load varies from 0.1 per cent to 4 per cent of the weight of the permanent gases in different times and locations. At higher elevations, water vapor rapidly grows less. Carbonic acid also diminishes, but not so fast. It is supposed that at very high levels the composition of the atmosphere is utterly changed. Ozone (another form of oxygen) is there as the spectroscope shows us, and it is supposed that finally helium (that light gas first found in the sun and now used to fill balloons) and other light gases predominate.15

Our evidence, then, indicates that the surface of the earth cooled first into igneous rocks. These were worked upon by ice, water, and air, and broken down into particles which were either deposited in place or carried into new locations. Thus arose under pressure the sedimentary, stratified rocks whose total depth is somewhere in the neighborhood of 80 miles. In turn these are eroded to form new layers, or to serve as the soil. Not all of these layers of stratified rocks are found in any one place. It is impossible to compare the age of the igneous rocks of different parts of earth but such a comparison can be made of the stratified in large measure because of the fossils they contain. We must not forget that both igneous and sedimentary rocks have often been changed under the influence of heat and pressure into metamorphic rocks which because of volcanic activity may now be found on the surface of the earth. Thus, the Palisades of the Hudson are of lava superimposed on sandstone. The stratified rocks are of three main classes:

1. Limestones, made of carbonates of calcium and magnesium

2. Sandstones and conglomerates, whose character varies with their composition

3. Shales which are consolidated mud

Regions underlain by shale are usually low and flat like the "Black Belt" of Alabama and the Mohawk Valley. The metamorphic rocks resulting from the above are as follows:

the limestone is turned into marble, sandstone turns into quartzite and shale into schist. The transformation of bituminous coal into anthracite may be mentioned also.

In as much as the soils are either formed in place by the decay of rocks, or else their particles have been moved to new locations by ice, water, or wind, we may classify them as:

Sedentary:

1. Residual gravels, clays sands
2. Peat, muck, swamp soils

Transported: 1. Alluvial

2. Glacial

3. Wind-blown, sand dunes, loess

Soils of these different types will have widely varying characters both as regards structure and chemical content. The particles of which they are composed will vary in size from the dust which forms clay to coarse gravel. Disregarding their water content they range in weight from peat at 40 pounds per cubic foot, through clay at 75, half sand and half clay at 96, to silicious sand at 110. The texture of the soil is determined by the arrangement of its particles which in turn determines the moisture it may hold. In fine clay the pore space is about 50 per cent but in coarse sand it is only 25 per cent. The importance of the relation of the soil to crops is now recognized and most of the soils of the country have been carefully studied as well as named.

In as much as the geologist measures time by eras rather than by years this appears to be the most logical place for the table showing the various eras, although hitherto any consideration of living organisms has been avoided.

PRESENT TIME

THE GEOLOGICAL TIME-TABLE

Psychozoic Era. Age of Man or Age of Reason

Includes the present or "recent time" and the time during which man attained his highest civilization, estimated to be probably less than 30,000 years

GEOLOGIC TIME

Cenozoic Era. Age of Mammalian Dominance

Glacial or Pleistocene time: last great ice age

Late Cenozoic or Pliocene and Miocene time: transformation of apes into man

Early Cenozoic or Oligocene and Miocene time: rise of higher mammals

Mesozoic Era. Age of Reptilian Dominance

Cretaceous period: rise of archaic or primitive mammals Comanchian period: rise of flowering plants and higher insects

Jurassic period: rise of birds and flying reptiles

Triassic period: rise of dinosaurs

Paleozoic Era. Age of Fish Dominance.

Permian period: rise of reptiles; another great ice age Pennsylvanian period: rise of insects and first time of marked coal accumulation

Mississippian period: rise of marine fishes

Devonian period: first known amphibians

Silurian period: first known land floras

Ordovician period: first known fresh water fishes
Cambrian period: first abundance of marine animals and
dominance of trilobites

Proterozoic Era. Age of Invertebrate Dominance
An early and a late ice age.

Archeozoic Era.

Origin of protoplasm and simplest life.

COSMIC TIME

Formative Era.

Birth and growth of the earth out of the spiral nebula of the sun. Beginnings of the atmosphere and hydrosphere, and of continental platforms and oceanic basins; no known geological record 16

The following tables will give some idea of the relative length of the different eras.

In 1917, Schuchert and Barrell estimated the geologic time ratios as indicated below. 18

To complete this brief summary of the facts of the inorganic world we must glance for a moment at some of the phenomena of motion which is quite as characteristic of matter as is mass. For long ages man had perceived through his various senses some of these movements and had classified them under such titles as sound, heat, electricity, light. We do not need to survey the earlier attempts to understand these phenomena but it is well to recall that a century ago heat was thought of as a fluid. With the discovery that atoms and their electrons and ions were moving as well as

molecules and masses, the way was opened for better understanding. A few atoms are breaking up in nature. Man can disrupt a few. He has a notion that if he knew more he could have a source of power beyond anything he now knows. That may or may not be true. It marks a great advance that he has learned something of the richness of nature and of the poverty of man. He hears sounds produced by vibration of molecules up to a certain limit when his ears cease to function. Insects appear to be better equipped. Man feels the atomic vibrations known as heat. He sees as colors some of the vibrations of electrons but far beyond the range of his vision are other rays. The waves of the wireless telegraph and radio are long-sometimes 15 miles from crest to crest. Passing the relatively short Roentgen and gamma rays, we reach the limit of present knowledge in the very short "cosmic" rays of Milliken. Substances opaque to the rays of light are easily penetrated by the short rays. To perceive these short rays we have to step them down to the range of our senses. Already we have learned to utilize many of them.

Matter, then, is not the dead, inert thing of which we used to talk. The sharp line man used to draw between matter and life becomes a hazy boundary belt separating two classes of natural phenomena which are, perhaps, as closely related as heat and light. The world becomes more marvelous, not less, and man stands in greater awe before its mysteries.

REFERENCES

1. J. BARRELL in LULL, Evolution of the Earth and Its Inhabitants, p. 42.

2. C. G. ABBOTT, The Earth and the Stars, p. 43.

3. Based on F. W. CLARKE, "Data of Geochemistry," Bulletin No. 491 (1911), U. S. Geological Survey.

4. S. A. ARRHENIUS, Chemistry in Modern Life, pp. 111, 112, 5. Ibid., p. 83.