imagine that that uniform cessation of organized life at one point, which seems to have conducted Sir Roderick Murchison and Professor Sedgwick to their conclusion, should have been thus a mere effect of accident. Accident has its laws, but uniformity is not one of them; and should the experience be invariable, as it already seems extensive, that immediately beneath the fucoidal beds organic remains cease, I do not see how the conclusion is to be avoided, that they represent the period in which at least _existences capable of preservation_ were first introduced. Every case of coincident cessation which has occurred since the determination of the second case, must be reckoned, not simply as an additional unit in evidence, but, on the principles which determine mathematical probability, as a unit multiplied first by the chances against its occurrence, regarded as a mere contingency in that exact formation, and second, by the sum of all the previous occurrences at the same point. In this curious question, however, which it must be the part of future explorers in the geological field definitely to settle, the Lamarckian can have no legitimate stake. It is but natural that, in his anxiety to secure an ultimate retreat for his hypothesis, he should desire to see that darkness in which ghosts love to walk settling down on the extreme verge of the geological horizon, and enveloping in its folds the first beginnings of life. But even did the cloud exist, it is, if I may so express myself, on its nearer side, where there is light,—not within nor beyond it, where there is none,—that the battle must be fought. It is to Geology _as it is known to be_, that the Lamarckian has appealed,—not to Geology as it is _not_ known to be. He has summoned into court _existing_ witnesses; and, finding their testimony unfavorable, he seeks to neutralize their evidence by calling from the “vasty deep,” of the unexamined and the obscure, witnesses that “won’t come,”—that by the legitimate authorities are not known even to exist,—and with which he himself is, on his own confession, wholly unacquainted, save in the old scholastic character of mere possibilities. The _possible_ fossil can have no more standing in this controversy than the “_possible angel_.” He tells us that we have not yet got down to that base-line of all the fossiliferous systems at which life first began; and very possibly we have not. But what of that? He has carried his appeal to Geology _as it is_;—he has referred his case to the testimony of the _known_ witnesses, for in no case can the _unknown_ ones be summoned or produced. It is on the evidence of the known, and the known only, that the exact value of his claims must be determined; and his appeal to the unknown serves but to show how thoroughly he himself feels that the actually ascertained evidence bears against him. The severe censure of Johnson on reasoners of this class is in no degree over-severe. “He who will determine,” said the