ated is enough to assure a lively interest in modern petrography, not merely on the part of geologists, but on the part of all intelligent persons who love to study the "wonderful wisdom and power of God as shown in his works." Together they promise far more for the future than has been fulfilled in the past.
We can not pause long enough to consider each of these four points in succession, but it will be worth our while to glance for a few moments at the last.
It is a question how far the popularly received distinction between dead and living matter can be made amenable to strict definition as long as we know so little of what the so-called "life force" is. As far as we can judge of the phenomena presented by the organic and mineral worlds, they differ rather in degree than in kind. This seems like a bold statement, and I am fully aware that it would be totally unwarranted except for the recent disclosures of the microscope in geology.
The chemistry of life is the chemistry of carbon; the chemistry of the rocks is the chemistry of silicon. Both are closely allied elements, with the property of forming extremely complex compounds, which become more or less unstable with a variation of external conditions. We are accustomed to regard unceasing change as a sign of life, and to look upon the rocks as unchanging, and therefore dead. But the microscope shows that this is a false conception. Not only do the component minerals assume a form as directly inherent in their nature as that of a plant; but, if the surrounding conditions become unfavorable, they change to other forms, and leave written in the rocks the records of their often complicated histories. The only difference seems to be in the relative slowness of the action. I say "seems to be," because I am by no means convinced of the absolute identity of the two processes.
In his recent annual address, the well-known President of the Geological Society of London, Prof. John W. Judd, has attempted to throw aside entirely the distinction between crystallized and living matter, and to bring the phenomena of change observed by the microscopist in rocks within the limits of such definitions of life as those of Lewes and Spencer. While we may be unwilling to follow him to this extent, we can but confess that the analogy to vital terms and processes recently used with so much power by Prof. Drummond in quite a different sphere is also capable of a valuable application in illustrating some of the modern aspects of geology. We may speak of the embryology of a mineral, of its histology, morphology, physiology, vitality, and suitability to its environment, designating by these terms phenomena which are at least analogous to those which they represent in biology.
