himself—it is "demonstrably contrary to fact" to allege that geology "knows nothing" of them. The science knows of them so well and so familiarly that "the last great depression" has become a stock phrase among Quaternary geologists—as referring to many ascertained phenomena which are capable of no other interpretation.
It may, however, be well asked how it is, if these three great facts have been established, that the conclusions flowing from them have not been followed up. The explanation is as easy as it is instructive. It has been due to that one cause which, perhaps more than any other, has impeded the advance of science—the blinding effect of invincible preconceptions. Sometimes these have been aggravated by such intellectual aversions as that which animates Prof. Huxley against everything connected with Christian theology. But many desperate preconceptions have other sources. The authority of great men who have fallen into some great error has been one of the barriers most difficult to breach. Of this kind perhaps the most memorable example was the power of Sir Isaac Newton to postpone for nearly a century and a half the establishment of the undulatory theory of light. The furious and contemptuous attacks made upon Dr. Thomas Young, when in our own day he revived that theory and poured the light of his own genius upon it, remind one very much of the temper and the spirit in which some men are now meeting those movements of discovery that tend to reopen questions which only ignorance had closed, and to give to old ideas a new and scientific basis. Then there has been another source of abounding prejudice. The shape in which those old ideas were at first presented has often been really deforming and erroneous. This has been pre-eminently the case with the form under which the idea of a deluge has come across the pathway of geology. At first men would not believe in the reality of fossil shells. When' this reality was proved to demonstration, then the supposition was entertained that they were carried into the solid rocks by the Noachian Deluge. The absurdity of this supposition was almost sickening, and it established a lasting sense of nausea in all the stomachs of geologists at the very mention of a deluge as coming at all within the cognizance of their science. This is just the attitude of mind which sets up the most insuperable preconceptions, and renders men insensible to the force of any evidence which even seems to look in the direction of their disgust. In this very article Prof. Huxley makes a confession upon this subject, which he does not mean as such, but which, nevertheless, is a confession most true and most significant. "At the present time," he says, "it is difficult to persuade serious scientific inquirers to occupy themselves in any way with the Noachian Deluge. They look at you with a
