Page:The evolution of worlds - Lowell.djvu/189

 CHAPTER VI A PLANET'S HISTORY Self-sustained Stage P to this point in our retrospective survey the long course of evolution has taken one line, that of dynamical separation of the system's parts with subsequent reunitement of them according to the laws of celestial mechanics. Of this action I have submitted the reader my brief: departing in it from common-law practice, in which the cause of action is short and the brief long. And I have, I trust, guarded against his appealing on exceptions.

From this point on we have two kinds of development to follow: the one intrinsic, the chemical; the other incidental, the physical. Not that, in a way, the one is divorcible from the other. For the physical makes possible the chemical by furnishing it the conditions to act. But in another sense, and that which is most thrust upon our notice, the two are independent. Thus oceans and land, hills and valleys, clouds and blue sky, as we know them,—everything, pretty much, which we associate with a world,—are not universal, 155