And a corresponding style of reasoning, based on the corresponding fact of the breaking up and piecemeal disappearance of the group of organized being, seems equally admissible. It is somewhat difficult to conceive how at least _many_ more volumes of the geologic record than the known ones could be got up without the _club_. Further,—so far as yet appears, the fish must have lived in advance of the reptile during the three protracted periods of the Old Red Sandstone, the two still more protracted periods of the Upper and Lower Silurians, and the perhaps more protracted period still of the Cambrian deposits;—in all, apparently, a greatly more extended space than that in which the reptile lived in advance of the quadrupedal mammal, or the quadrupedal mammal lived in advance of man. On principles somewhat similar to those on which, with reference to the average term of life, the genealogist fixes the probable period of some birth in his chain of succession of which he cannot determine the exact date, it seems natural to infer that the _birth_ of the fish should have taken place at least not earlier than the times of the Cambrian system. There is another consideration, of at least equal, if not greater weight. A general correspondence is found to obtain in widely-separated localities, in the organic contents of that lowest band of the Lower Silurian or Cambrian system in which fossils have been detected. In Russia, in Sweden, in Norway, in the Lake district of England, and in the United States, there are certain rocks which occupy relatively the same place, and enclose what may be described generally as the same remains. They occur in Scandinavia as that “fucoidal band” of Sir Roderick Murchison which forms the base of the vast Palæozoic basin of the Baltic; they exist in Cumberland and Westmoreland as the Skiddaw slates of Professor Sedgwick, and bear also their fucoidal impressions, blent with graptolites; they are present in North America as those Potsdam sandstones of the States’ geologists in which fucoids so abound, mixed with a minute lingula, that they impart to some portions of the strata a carboniferous character. But with these deep-lying beds in all the several localities, thousands of miles apart, in which their passage into the inferior deposits has been traced, fossils cease. And why cease with them? In one locality the ancient ocean may have been of such a depth in the period immediately _previous_, and represented, in consequence, by the strata immediately _beneath_, that no animal could have _lived_ at its bottom,—though I do not well see why the remains of those animals who, like the shark and pilot-fish, are frequently seen swimming over the profoundest depths, might not, did such exist at the time, be notwithstanding _found_ at its bottom; or in another locality every trace of organization in the nether rocks may have been obliterated, at some posterior period, by fire. But it is difficult to