Page:Popular Science Monthly Volume 2.djvu/745

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those set forth long afterward by Werner, we come to Hutton, with whom in fact rational geology commences. For the untenable Neptunist hypothesis, asserting a once-universal aqueous action unlike the present, Hutton substituted an aqueous action, marine and fluviatile, continuously operating as we now see it, antagonized by a periodic igneous action: he recognized denudation as producing mountains and valleys; he denied so-called primitive rocks; he asserted metamorphism; he taught the meaning of unconformity. Since his day rapid advances in the same direction had been made. William Smith, by establishing the order of superposition of strata throughout England, prepared the way for positive generalizations; and, by showing that contained fossils are better tests of correspondence among strata than mineral characters, laid the basis for subsequent classifications. The better data thus obtained, theory quickly turned to account. In his "Principles of Geology," Lyell elaborately worked out the uniformitarian doctrine—the doctrine that the earth's crust has been brought to its present complex structure by the continuous operation of forces like those we see still at work. More recently, Prof. Ramsay's theory of lake-formation by glaciers has helped in the interpretation; and by him, as well as by Prof. Huxley, much has been done toward elucidating past distributions of continents and oceans. Nor must we forget Mallet's "Theory of Earthquakes"—the only scientific explanation of them yet given. And there must be added another fact of moment. Criticism has done far more here than abroad, toward overthrowing the crude hypothesis of universal "systems" of strata, which succeeded the still cruder hypothesis of universal strata, enunciated by Werner.

That our contributions to Biological Science have in these later times not been unimportant, may, I think, be also maintained. Just noting that the "natural system" of plant-classification, though French by development, is English by origin, since Ray made its first great division, and sketched out some of its subdivisions, we come, among English botanists, to Brown. He made a series of investigations in the morphology, classification, and distribution of plants, which in number and importance have never been equalled: the "Prodromus Floræ Novæ Hollandia" is the greatest achievement in classification since Jussieu's "Natural Orders." Brown, too, it was who solved the mystery of plant-fertilization. Again, there is the conception that existing plant-distribution has been determined by past geological and physical changes—a conception we owe to Dr. Hooker, who has given us sundry wide interpretations in pursuance of it. In Animal-physiology there is Sir Charles Bell's discovery respecting the sensory and motor functions of the nerve-roots in the spinal cord; and this underlies multitudinous interpretations of organic phenomena. More recently we have had Mr. Darwin's great addition to biological science. Following in the steps of his grandfather, who had anti-