the hypothesis that the globe was in a state unfavourable to the development of organic life by reason of the greater influence then exercised by its proper heat upon the phenomena at the surface, than after a considerable thickness of non-conducting materials (the earlier strata,) had become effectual in retarding the flow of heat from within. At all events, for us, reasoning from facts observed, the origin of our system of organic life is to be placed in the midst of the period of primary strata. "The earliest forms of life known to geology are not, as might perhaps be expected, plants, but animals; they are not of the lowest grade of organization merely; zoophyta far advanced in structure, (lamelliferous corals); brachiopodous bivalves, of three genera, were found by myself on Snowdon, but no distinct traces of plants. The number of species of this early fauna is extremely small, but there is about them no mark of inferiority,-no extraordinary simplicity. "From this origin of organic life there is no break in the vast chain of organic development till we reach the existing order of things: no one geological period, long or short, no one series of stratified rocks, is everywhere devoid of traces of life; the world once inhabited has apparently never for any ascertainable period, been totally despoiled of its living wonders; but there have been many changes in the individual forms, great alterations in the generic assemblages, entire revolutions in the relative number and development of the several classes. Thus the systems of life have been varied from time to time to suit the altered condition of the planet, but never extinguished; the earth once freed from its early inadequacy to support life according to the appointed laws of life, has since been prolific of vegetable and animal existence. "The proportionate number of organic forms has gone on even gradually (see my Guide to Geology,) augmenting from the dozen species of the Snowdon slates, through the twelve hundred and more species of the oolite, the four thousand forms of the tertiary eras, to the multitudes of existing things. The change of organic structure is also, in some degree, proportioned to the time elapsed; tried by the cephalopodous mollusca, we see perish first the orthoceratites, then the Belemnites and Ammonites, while nautilus and sepia exist to represent this class in existing nature. The development of the different classes of animals is usually thought to exhibit a similar relation, as if nature had been continually improved from the moment of the origin of life; but this opinion is, if taken generally, one of the least certain of all the general notions now current, because of a radical defect in the reasoning. This defect consists in assuming into one induction the terrestrial and marine races of animals. Now, as the higher forms of life are terrestrial, and the remains of terrestrial things are only by accident mixed with the spoils of the sea, it is no wonder that mammalia and birds are rarely suspected even to occur among the buried spoils of the ocean. However, the Didelphis of Stonesfield is enough to cast a doubt on this notion, which should be more critically examined by a logical process. It should be inquired what is the order of development among the marine races on one hand, and the terrestrial groups on the other. The latter are too few, in a fossil state, to justify any decision; the former supply certain evidence. The order of development is, zoophyta and brachiopodous conchifera; the same groups, with the addition of plagimyonous conchifera, gasteropoda, cephalopoda, fishes; the same, with the addition of reptiles; the same, with one solitary didelphis; the same, without didelphis or any other quadruped; the same, with marine and terrestrial quadrupeds; existing creation. "Is the present creation of life a continuation of the previous ones,- -a term of the same long series of communicated being?-I answer, Yes! But not as the offspring is a continuation of its parent. The present crocodiles are not thus derived from the Teleosaurus of Caen, by indefinite change through time and circumstance, as St. Hilaire's and Lamarck's, (and Goethe's ?) speculations might lead to suppose; but the existing forms of life resemble those of times gone by, because the general aspect of the physical conditions of the world has always been, since the origin of life on the globe, decidedly analogous, and they differ from them because the co-relation of life and physical conditions is strict and necessary, so that all the variations of these conditions are represented in the phases of organic structure, while all their general agreements are also represented by the conformity of the great principles of structure in the beings of every geological age, and the often repeated analogies and parallelisms of series of forms, between different geological periods, which we now hail as a law of nature, when comparing America or Australia with Africa, Asia, or Europe. "We are not, then, in a different system of nature, properly so called, from those which have been created and have been suffered to pass away before the birth of man! but in a forward part of the same system, whose law of progression is fixed, though from time to time the signification of the terms varies. The full and complete system of organic life now on the globe includes all the effects of land and sea, warmth and cold, divided regions, and all the other things which are the diversifying causes of nature; and it is no wonder if before this land was raised from the deep, and the present distinction of natural regions was produced, there was not the same extreme variety of natural productions. Till that variety was occasioned on the globe it was not the fitting place for intellectual man that now it is; for surely among the other uses and co-relations of the visible creation this is one; by its inexhaustible diversity and ever-growing newness to interest with a perpetual charm the growing mind of a rational being, and lead him by a flowery path to the full cultivation of the divine thing within him, which raises him above all that his senses make known, and thus to fit him for the highest contemplation of which he is capable, viz., the relation which he bears to the unseen Author of all this visible material world. "Thus, to the mind of a geologist nature is one glorious book; one system of appointed and associated law, independent of time and exempt from change, but operating under conditions which vary with time and place; the past has prepared the present, the present explains the past and points to the future." |