With respect, then, to the first of these propositions, we may ask whether the theory of the progressive development of animal and vegetable life, and their successive advancement from a simple to a more perfect state, has any secure foundation in fact? No geologists who are in possession of all the data now established respecting fossil remains, will for a moment contend for the doctrine in all its detail, as laid down by the distinguished philosopher to whose opinions we have referred: but naturalists, who are not unacquainted with recent discoveries, continue to defend it in a modified form. They say that in the first period of the world (by which they mean the earliest of which we have yet brought to light any memorials), the vegetation was characterized by a predominance of cryptogamic plants, while the animals which coexisted were almost entirely confined to zoophytes, testacea, and a few fish. Plants of a less simple structure, coniferæ and cycadeæ, flourished largely in the next epoch, when oviparous reptiles began also to abound. Lastly, the terrestrial flora became most diversified and most perfect when the highest orders of animals, the mammalia and birds, were called into existence. Now in the first place, it may be observed, that many naturalists are guilty of no small inconsistency in endeavoring to connect the phenomena of the earliest vegetation with a nascent condition of organic life, and at the same time to deduce from the numerical predominance of certain forms, the greater heat or uniformity of the ancient climate. The arguments in favor of the latter conclusion are without any force, unless we can assume that the rules followed by the Author of Nature in the creation and distribution of organic beings were the same formerly as now; and that, as certain families of animals and plants are now most abundant in, or exclusively confined to regions where there is a certain temperature, a certain degree of humidity, a certain intensity of light, and other conditions, so also analogous phenomena were exhibited at every former era. If this postulate be denied, and the prevalence of particular families be declared to depend on a certain order of precedence in the introduction of different classes into the earth, and if it be maintained that the standard of organization was raised successively, we must then ascribe the numerical preponderance, in the earlier ages, of plants of simpler structure, _not to the heat_, or other climatal conditions, but to those different laws which regulate organic life in newly created worlds.