The seventh day is the modern or human era in geology; and, though it can not yet boast of any physical changes so great as those of past periods, it is still of much interest, as affording the facts on which we must depend for explanations of past changes; and as immediately connected in time with those later tertiary periods which afford so many curious problems to the geological student. The actual connection of the human with preceding periods is still involved in some obscurity; and, as we shall see, there has recently been a strong tendency to throw back the origin of man into prehistoric ages of enormous length, on grounds which are, however, much less certain than is commonly imagined. This question we have to examine; but before entering upon it may shortly sketch the actual import of the statements of the Hebrew Scriptures respecting what may be called the prehistoric duration of the human species. This is the more necessary, as the most crude notions seem very widely to prevail on the subject. I shall, therefore, in this place notice some general facts deducible from the Bible, and which may be useful in appreciating the true relation of the human era to those which preceded it. It will be understood that I shall endeavor merely to present a picture of what the Bible actually teaches, and which any one can verify by reading the book of Genesis. 1. The local centre of creation of the human species, and probably of a group of creatures coeval with it, was Eden; a country of which the Scriptures give a somewhat minute geographical description. It was evidently a district of Western Asia; and, from its possession of several important rivers, rather a region or large territory than a limited spot, such as many, who have discussed the question of the site of Eden, seem to suppose. In this view it is a matter of no moment to fix its site more nearly than the indication of the Bible that it included the sources and probably large portions of the valleys of the Tigris, the Euphrates, and perhaps the Oxus and Jaxartes. Into the minor difficulties respecting the site of Eden it would be unprofitable to enter, and it will matter little if we accept that view, which, however, I think less probable, that it was placed in the lower part of the valley of the Euphrates. I may merely mention one particular of the Biblical description, because it throws light on the great antiquity of this geographical delineation, and has been strangely misconceived by expositors--the relation of those rivers to Cush or Ethiopia and Havilah, a tribal name derived from that of a grandson of Cush. On consulting the tenth chapter of Genesis, it will be found that the Cushites under Nimrod, very soon after the deluge, are stated to have pushed their migrations and conquests along the Tigris to the northward, and established there the first empire. It is probably this primitive Cushite empire, called Ethiopia in our