Either the geological record is sufficiently complete to afford us a means of determining the order in which animals have made their appearance on the globe or it is not. If it is, the determination of that order is little more than a mere matter of observation; if it is not, then natural science neither affirms nor refutes the "fourfold order," but is simply silent.
The series of the fossiliferous deposits, which contain the remains of the animals which have lived on the earth in past ages of its history, and which can alone afford the evidence required by natural science of the order of appearance of their different species, may be grouped in the manner shown in the left-hand column of the following table, the oldest being at the bottom:--
Formations First known appearance of Quaternary. Pliocene. Miocene. Eocene. Vertebrate _air_-population (Bats). { 82} Cretaceous. Jurassic Vertebrate _air_-population (Birds and Pterodactyles). Triassic. Upper Palæozoic. Middle Palæozoic Vertebrate _land_-population (Amphibia, Reptilia [?]). Lower Palæozoic. Silurian. Vertebrate _water_-population (Fishes). Invertebrate _air_ and _land_-population (Flying Insects and Scorpions). Cambrian Invertebrate _water_-population (much earlier, if _Eozoon_ is animal).
In the right-hand column I have noted the group of strata in which, according to our present information, the _land_, _air_, and _water_-populations respectively appear for the first time; and in consequence of the ambiguity about the meaning of "fowl," I have separately indicated the first appearance of bats, birds, flying reptiles, and flying insects. It will be observed that, if "fowl" means only "bird," or at most flying vertebrate, then the first certain evidence of the latter, in the Jurassic epoch, is posterior to the first appearance of truly terrestrial _Amphibia_, and possibly of true reptiles, in the Carboniferous epoch (Middle Palæozoic) by a prodigious interval of time.
The water-population of vertebrated animals first appears in the Upper Silurian.[12] Therefore, if we found ourselves on vertebrated animals and take "fowl" to mean birds only, or, at most, flying vertebrates, natural science says that the order of succession was water, land, and air-population, and { 83} not--as Mr. Gladstone, founding himself on Genesis, says--water, air, land-population. If a chronicler of Greece affirmed that the age of Alexander preceded that of Pericles and immediately succeeded that of the Trojan war, Mr. Gladstone would hardly say that this order is "understood to have been so affirmed by historical science that it may be taken as a demonstrated conclusion and established fact." Yet natural science "affirms" his "fourfold order" to exactly the same extent--neither more nor less.