Page:Popular Science Monthly Volume 10.djvu/55

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45
PROFESSOR HUXLEY'S LECTURES.

things has had only a limited duration, and that at some period in the past the state of things which we now know (substantially, though not, of course, in all its details) arose and came into existence without any precedent condition from which it could have naturally proceeded. The third hypothesis also assumes that the present order of Nature has had but a limited duration, but it supposes that the present order of things proceeded by a natural process from an antecedent order, and that from another antecedent order, and so on; and on this hypothesis the attempt to fix any limit at which we could assign the commencement of this series of changes is given up. I am very anxious that you shall realize what these three hypotheses actually mean; that is to say; what they involve, if you can imagine a spectator to have been present during the period to which they refer. On the first hypothesis, however far back in time you place that spectator, he would have seen a world essentially, though not perhaps in all its details, similar to that which now exists. The animals which existed would be the ancestors of those which now exist, and like them; the plants in like manner would be such as we have now; and the supposition is that, at however distant a period of time you place your observer, he would still find mountains, plains, and waters, with animal and vegetable products flourishing upon them and sporting in them just as he finds now. That view has been held. It was a favorite fancy of antiquity, and has survived toward the present day. It is worthy of remark that it is an hypothesis which is not inconsistent with what geologists are familiar with as the doctrine of Uniformitarianism. That doctrine was held by Hutton, and in his earlier days by Lyell. For Hutton was struck with the demonstration of astronomers that the perturbations of the planetary bodies, however great they may be, yet sooner or later right themselves, and that the solar system contained within itself a self-adjusting power by which these aberrations were all brought back to an equilibrium.

Hutton imagined that something of the same kind may go on in the earth, although no one recognized more clearly than he the fact that the dry land is being constantly washed down by rain and rivers and deposited in the sea, and that thus in a certain length of time, greater or shorter, the inequalities of the earth's surface must be leveled, and its high lands brought down to the sea. Then, taking into account the internal forces of Nature, by which upheavals of the sea-bottom give rise to new land, he thought that these operations might naturally compensate each other, and thus, for any assignable time, the general features of the earth might remain what they are. And, inasmuch as there need be no limit under these circumstances to the propagation of animals and plants, it is clear that the logical development of this idea might lead to the conception of the eternity of the world. Not that I mean to say that either Hutton or Lyell held this conception—assuredly not; they would have been the first to repu-