As far as it can penetrate into the mysteries of creation, Physical Astronomy has endeavoured to show how the solar system may have been formed out of a mass of nebulous matter. Furthermore, as has already been adduced in evidence, that at one time the earth must have been a molten, liquid globe surrounded by vapours of metals, metalloids, gases, and finally by water; and even goes the length of supposing that the planets were evolved to something approaching their present state, long before the sun attained its present form. Following up this hypothesis, it is more than probable that the sun had not attained that form when this fourth period began, and, although capable of emitting light early in the first period, still required a vast amount of evolution to reduce it to the brilliant globe now seen in the heavens. Everybody knows that plants grow without sunshine, and it is generally believed that the primary forests of the earth grew most rapidly in a moist, stifling atmosphere, which neither admitted of animal life, nor could be penetrated by sunshine. Thus Physical Astronomy cannot say that the sun could not have been made into its present state until near the end of this fourth period. It _may_ have been as bright as it is now, though very probably not, as we shall see in due time; but it could not _shine_ upon the earth, neither could the earth, nor anything thereon, see it. It is not necessary to say anything about the moon, as it only reflects sunlight, and the reflection could not reach the earth if the light could not. In the fifth period the waters were _let_ "bring forth the moving creature that hath life, and fowl that may fly above the earth in the open firmament of heaven." Here again spontaneous generation may have been provided for beforehand, the same as in the case of vegetation. Also it is said "God created great whales," and it is to be observed that this is only the second time that creation has been mentioned in the book, and would seem to teach that _making_, or evolution, was the most active agent at work in the construction of the earth--and, we may add, of the universe. The sixth period was one almost exclusively of evolution, unless it should be considered that spontaneous generation is a different, and newly discovered process. In it God _made_ the beast of the earth, cattle, and everything that creepeth upon the earth, after his kind. Last of all: "God said, let us make man in our image, after our likeness." Thus it appears that the only work of creation done in this period was that of creating man, and even that _after_ some length of time and work had been expended in _making_ or _evolution_, which may have extended over a very considerable portion of the fifty millions of years corresponding to it.