liquid water, and over a part of the surface of the water, while animals inhabit the atmosphere and the watery envelope or hydrosphere. What is usually called the land is but the upper surface of a third sphere of solid rock which is denominated by geologists as the lithosphere; this lithosphere contains another and important portion of the substances which are produced for the welfare of mankind. The lithosphere, the hydrosphere, and the atmosphere, together with the plants and animals of the earth, constitute the environment of mankind. All human industries are therefore included in the consideration of the sources of the substances which men produce.
Hence, when we classify the substances of the environment in these five groups, we classify them in coordinate groups from the consideration of the environment of man, though we may afterward subclassify every one of these groups. We are not classifying substances as fundamental classes, but we are classifying the substances used by man as fundamental classes, and the subclassification will still include only the substances used by man.
Man is a denizen of the air; he lives on that portion of the surface of the lithosphere which is called dry land, where the watery envelope is vapor. Thus he is directly connected in his environment with the three spheres and utilizes them for his purposes. Man is not content with thenatural products of the lithosphere, but he seeks to improve them. He is not content with the natural products of the hydrosphere, but he seeks to improve the water by purifying it or by charging it with other substances. He is not content to drink like the beast from the pool or the stream, but he seeks to bring the water to himself in the most convenient and best manner in which to enjoy it. Man is not even content with breathing the atmosphere, but he seeks to procure it in its purity, so he ventilates his habitation and otherwise secures the greatest purity. Man is not content with the plants as they are furnished by nature, so he improves them by cultivation and multiplies those which are useful to him and destroys
