When during a long epoch a continent, slowly sinking, gives place to a far-spreading ocean some miles in depth, at the bottom of which no deposits from rivers or abraded shores can be thrown down; and when, after some enormous period, this ocean-bottom is gradually elevated and becomes the site for new strata; it is clear that the fossils contained in these new strata are likely to have but little in common with the fossils of the strata below them. Take, in illustration, the case of the North Atlantic. We have already named the fact that between this country and the United States, the ocean-bottom is being covered with a deposit of chalk--a deposit which has been forming, probably, ever since there occurred that great depression of the Earth's crust from which the Atlantic resulted in remote geologic times. This chalk consists of the minute shells of _Foraminifera_, sprinkled with remains of small _Entomostraca_, and probably a few Pteropod-shells; though the sounding lines have not yet brought up any of these last. Thus, in so far as all high forms of life are concerned, this new chalk-formation must be a blank. At rare intervals, perhaps, a polar bear, drifted on an iceberg, may have its bones scattered over the bed; or a dead, decaying whale may similarly leave traces. But such remains must be so rare, that this new chalk-formation, if accessible, might be examined for a century before any of them were disclosed. If now, some millions of years hence, the Atlantic-bed should be raised, and estuary deposits or shore deposits laid upon it, these would contain remains of a Flora and a Fauna so distinct from everything below them, as to appear like a new creation. Thus, along with continuity of life on the Earth's surface, there not only _may_ be, but there _must_ be, great gaps in the series of fossils; and hence these gaps are no evidence against the doctrine of Evolution. * * * * * One other current assumption remains to be criticized; and it is the one on which, more than on any other, depends the view taken respecting the question of development.