154 THE POPULAR SCIENCE MONTHLY. 



seems like the lower Amazon, too broad for us to see its banks, 

 coming from the high Andes and the lower plains, and going to 

 its rest in the ocean. 



According to the well-approved nebular hypothesis of Kant 

 and Laplace, the material of our earth and moon became sepa- 

 rated from the condensing mass of the sun after the outer planets 

 had been similarly produced, but before the birth of Venus and 

 Mercury. At early stages in the condensation of the revolving 

 nebula, it had thrown off successively the portions of matter 

 which were afterward gathered, by their independent condensa- 

 tion and revolution, to form Neptune, Uranus, Saturn, Jupiter, 

 and Mars ; while another portion, which was probably never united 

 like the other planets, made the many small asteroids. The mat- 

 ter which has been changed into our splendidly luminous sun was 

 at one time very attenuated and occupied the whole space inclosed 

 by the orbit of the outermost planet, which was developed from 

 a comparatively very small cloud or ring of this matter, centrif u- 

 gally detached from the revolving exceedingly tenuous mass. In 

 like manner the material of each of the planets, including the 

 earth, was shed from the whirling nebula at times during its 

 decrease in volume when its circumference was approximately 

 coincident with their orbits. 



Again, in their turn the planetary masses have undergone the 

 same evolutionary process, taking a rotary motion and throw- 

 ing off, as they condensed, the material which now circles about 

 them in the shape of moons and rings. In the case of our own 

 planet and its single large satellite, probably the far greater part 

 of the original cloud or ring whence they were produced had 

 assumed a somewhat globular or discoid form and taken a move- 

 ment of revolution which still continues as the earth's daily rota- 

 tion, before the moon's mass was separated from that of the 

 earth. It seems to me, however, very improbable that the 

 present contour of our globe should preserve, as suggested by 

 Fisher, the scars of this loss in the depressions of the deep ocean 

 basins. 



Many relatively small portions of the ring of matter produc- 

 ing the earth and moon may have become early separated from 

 the chief condensing mass, and after its division in our globe and 

 its satellite have been drawn by gravitation into them, marring 

 the face of the moon, as Gilbert supposes, with its multitudes of 

 both small and very large crateriform scars. On the earth, too, 

 if this hypothesis be true, such falling asteroid-like bodies must 

 also have made similar small and huge blots by their violent im- . 

 pact; but they evidently were effaced by the slow processes 'of 

 atmospheric and stream erosion, or in basin areas were deeply 

 covered by sediments, before the formation of the oldest of our 



