soil it readily took root and flourished like a vigorous tree, bearing rich fruit and sending its seeds into every land upon the earth where knowledge is sought for.
At first progress was necessarily slow, mistakes were frequent, and a general interest in the subject was almost lacking. But as one point after another was gained, and as a deeper insight into the problems presented was secured, the number of workers steadily increased. The patient labors of such pioneers as Zirkel, Vogelsang, and Rosenbusch can never be forgotten by those who can now avail themselves of their years of toil in a few months.
Interesting and surprising results were secured at the outset by the new science, but they were mineralogical rather than geological in their bearing. It is only now, after thirty years of preparation, that the time is fully ripe for the application of the new petrography to some of the deepest questions of theoretical geology. This it is which affords almost the only hopeful means of dealing with the records of the crystalline strata of the earth, which undoubtedly contain the longest, as they do by far the darkest, chapter of its history. What paleontology has already done and is still doing for the more superficial strata in which organic remains are preserved, the microscope must do for the crystalline rocks, whether volcanic, plutonic, or metamorphic. These contain their own life-histories, written in characters which need only to be carefully studied in order to be properly interpreted.
The purely mineralogical services of the microscope need not here concern us, but it may be pertinent to inquire. What specific classes of facts has this instrument disclosed and what new ideas has it suggested that entitle it to so high a consideration by those who are interested with the broader problems of the earth's history? To this inquiry we may answer:
1. The microscope has shed light into darkness; and, by its promise of results, has stimulated an enthusiastic cultivation of a most important but hitherto neglected field.
2. It has shown us that the internal structure of the commonest pebble is not less admirable, delicate, and exquisitely beautiful than that of a living organism.
3. It has already thrown much light upon the origin of many of the crystalline rocks—both massive and schists—by allowing us to judge of the conditions under which they must have been formed.
4. Most wonderful of all, it has taught us that the components of the "everlasting hills" are not mere masses of dull, unchangeable, inert matter, but that, in so far as constant change of form and composition to accord with altered conditions is a sign of life, they live.
Any single one of the four points which I have here enumer-
