Page:Popular Science Monthly Volume 47.djvu/319

Rh of some sizable lumps of black diamond in the Cañon Diablo meteorite led Mr. Huntington to investigate further in the very extensive collection belonging to Harvard University, and he found, on dissolving sample chips as thoroughly as possible, that a powder remained whose resistance to corrosives and invincible hardness are signs manual of the sovereign of stones. We find, too, in these iron meteorites gases absorbed, such as those at whose door we have laid the responsibility for the production of volcanic eruptions.

Since the weight of our earth and the evidence of sample fragments of planetary matter point to its being mainly iron—if we may not only say that this is an iron age but also an iron world—is it any wonder that iron is so widely distributed, or that it is the universal pigment, even dyeing the blood of our veins? But there is further evidence on these lines at which we have as yet but hinted. We said that meteorites were connected in composition with terrestrial rocks. It is in fact true that native iron similar in structure to that of meteorites is found in some basaltic dikes in Greenland as large masses, and in microscopic quantities elsewhere, and it seems almost certain that it has been torn from the depths of the earth. The rock in which the diamonds occur in the Kimberly mine (and everywhere else where they occur originally, and not in sand and gravel, they are in similar connection) is very rich in iron, is composed of minerals common in meteorites, but is devoid of quartz and feldspar, the commonest minerals of the upper crust. Practically, all the minerals of the meteorites occur native in the earth's crust, but only sparingly, except in connection with rocks that have risen through fissures from beneath. They do not occur in connection with all these rocks, but only in connection with rocks like the Kimberly rock, which are darker and heavier and less siliceous. There are a number of reasons for supposing that these darker and heavier igneous rocks, containing more iron and less silica, have a deeper source than those composed mainly of quartz and feldspar, but we will mention only one. Our earth is wrapped with an atmosphere of oxygen, an element exceedingly ready to enter into combination—so much so that in all our ordinary surface rocks all the other elements are combined with oxygen as much as can be. Now iron, as is well known, has the power of combining with oxygen either in the proportion of three of oxygen to two of iron or in even proportions. The former compounds which have more oxygen are those found in ordinary rust, and are much more readily formed, being the so-called ferric compounds. They are often yellow or red in color. The other compounds containing less oxygen—the so-called ferrous compounds—very readily absorb more oxygen. In fact, their readiness to do so under the