shrinkages of the earth's interior caused by its gradual cooling, and to the unequal deposition of material by water on different parts of its surface.[67] The more full discussion of these points belongs, however, to a future chapter. These greater movements of the crust, would, as already stated, coincide to some extent with the later creative days in the manner indicated below: ================================================================== Collapse of crust at close of | Close of Fourth AEon, Eozoic Time, | and beginning of Fifth. ------------------------------------------------------------------ Collapse in Permian Period and | Middle of Fifth AEon. end of Palaeozoic Time, | ------------------------------------------------------------------ Great subsidence and collapse | Close of Fifth AEon, and beginning at close of Mesozoic Age, | of Sixth. ------------------------------------------------------------------ Great subsidence of the | End of Sixth AEon. Pleistocene or Glacial Age, | ================================================================== The question recurs--Why are God's days so long? He is not like us, a being of yesterday. He is "from Olam to Olam," and even in human history one day is with him as a thousand years; and we who live in these later days of the world know full well how slow the march of his plan has been even in human history. We shall know in the endless ages of a future eternity that even to us these long creative days may at last become but as watches in the night. CHAPTER VII. THE ATMOSPHERE. "And God said, Let there be an expanse between the waters; and let it separate the waters from the waters. And God made the expanse, and separated the waters which are under the expanse from the waters which are over the expanse: and it was so. And God called the expanse Heaven. And the evening and the morning were the second day."--Genesis i. 6-8. At the opening of the period to which we are now introduced the earth was covered by the waters, and these were in such a condition that there was no distinction between the seas and the clouds. No atmosphere separated them, or, in other words, dense fogs and mists everywhere rested on the surface of the primeval ocean. To understand as far as possible the precise condition of the earth's surface at this period, it will be necessary to notice the present constitution of the atmosphere, especially in its relations to aqueous vapor.