CHAPTER XI.

GEOLOGY.

SECT. I. TRACES OF PLAN IN FOSSIL REMAINS.

We have discovered proofs of One Designing Mind in the organization of plants and animals in the existing epoch of our earth's history. But our earth has also had a past history. Could our globe relate the story of the scenes which have taken place on its surface, what a thrilling narrative would it furnish! The dumb earth possesses no power of detailing its past changes in language, but it has carefully prepared in its crust, records, which man has faculties to decipher, and which he may succeed in deciphering, provided he proceeds with pains and caution, and in the spirit and method of the induction of Bacon. The archeologist draws conclusions from the style of the ancient buildings examined by him, and finds an entire history in the coins which he disinters from their crumbling ruins; the geologist can also gather most important instruction as to the past from the still more valuable relics which are preserved in the rocks and dust of our earth. It will be found that geology extends our argument in respect of time throughout ages which cannot be numbered, and shews that God has been proceeding in a pre-arranged system from the commencement of creation.

First, On examining the deposits of geological eras, there is little difficulty in shewing that plants and animals have been constructed on the same general plan from the beginning.

Secondly, As the organisms of different geological eras, while formed on a general model, do yet differ widely from each other, the question is started, Is there a predetermined scheme in the successive appearances of animated beings; or, in other words, is there plan in the creation of classes, orders, genera, and species? It should be frankly acknowledged that geology is not yet prepared to give a certain and decided answer to this question. Still it has revealed phenomena which raise the question, and supplied some facts which may help to answer it, and furnishes proofs that there is order in the succession of animal races, even though it has not yet entitled us to say with confidence that we have discovered the plan. Geology thus opens up glimpses not only of a plan in respect of contemporaneous and existing nature, but of a plan in respect of past and successive nature. Thirdly, Geology has a further, and this a most important principle to reveal. It shews not only a uniform but an advancing plan. It does more, it unrolls a prophetic scroll, in which the earlier animated creation points on to the later, and in which the later comes as a fulfilment of the anticipation of the earlier. These are the topics to be discussed in this section.

I. UNIFORM PLAN.-The silex dissolved in the water of some ancient spring or lake has often entirely replaced the materials of a stem, taking not merely the place but assuming the very form and essential character of every cell and modification of it, so that, when subjected to the wheel of the lapidary, slices may be cut which, under the microscope, reveal the most minute structure of the ori

ginal plant. The elements, the living stones of the extinct vegetable, have thus been wonderfully preserved for our examination and instruction. Even when scarcely a trace of vegetable structure can be detected, the inorganic material of the earth's crust-the clay or mud of some ancient lake or swamp, or the sand now forming the stone of some modern quarry-has come into the place of the organic framework, or received such an impression by contact, that we have thus singularly preserved for our inspection an accurate representation of a fruit or of the venation of a leaf torn from the parent plant by a passing hurricane, or shed naturally in the autumn of some one of those countless years which elapsed before man appeared. These relics shew that the same system governed the building up of the ancient tree-ferns, palms, and pines, as still regulates the formation of those that surround us with all their symmetry and gracefulness. How interesting is it to trace on these fossils, as we have often done, the same crossing or winding spirals, and the same rhomboidal figures produced by their intersection, as we have in the tree-ferns and firs still growing on our earth; a proof that the spiral then, as now, regulated the position of the appendages of the plant.

A similar conclusion may be drawn from the animal remains imbedded in the crust of the earth. The Uraster obtusus of the older Silurian rocks has a striking resemblance to the Uraster rubens of our own coasts; the radiate arrangement of parts is identical in both. The earliest Crustacea known to us, the Trilobites, present the articulate type so familiar to us in the lobster and crab. The shell of the little Nucula varicosa, found in the same old strata, must have given protection to an animal like that of our living species of that same genus. The earliest spiral shells which have been discovered are

governed by the same mathematical principles as those which the molluscs are following at this day in the construction of their habitations. The vertebrate column and appendages of fossil fish, bird, and mammal, whether of the older or more recent geological epochs, were formed on the same models as those of the same models that still people our earth and its waters. The teeth of extinct animals were constructed on the same general plan as those of existing species, and this, whether we view them as regards form, position, number, or minute structure.

Indeed, the geologist proceeds, and is entitled-by a large induction of facts, and the verifications which are ever casting up-to proceed, on the principles which we have all along been illustrating in this treatise. It is seldom that he finds a fossil plant or animal entire; most commonly he falls in with only a fragment; yet this fragment, if it be a significant one, enables him to reconstruct the whole. The process of theoretical reconstruction is conducted on those very principles of homology and teleology which we have shewn to pervade all organic nature. The palæontologist supposes that the whole organism, whether plant or animal, was constructed on a plan; that there were answerable parts in the genus or species, and a series of homotypes in the individual; and he goes on confidently to supply the wanting parts on the principle of homology. He proceeds, too, on the principle of final cause; he supposes that the part had an end to serve, and that there would be a conformity of every other organ to fulfil that end. By means of these two principles he can often, when he is in possession of but a fragment, make the entire organism stand before us with all its harmonies and its fitnesses. When at any time he falls in with an entire fossil organism, he finds that his principles are verified, and that he is entitled to pro

ceed on them. In the next section we shall shew how he uses the principle of final cause; in this section we are to observe him as proceeding upon model forms in his investigations of the various kingdoms of nature.

Fossil Plants.-Certain vegetable organs have been imperfectly preserved in the earth's strata, or have undergone such changes that it is often difficult to detect their relations. The palæontologist does not hesitate to trace up these to one or other of the great leading divisions of the vegetable kingdom. He may not have before him, or be able to find, some one part of the organism-say the seed, so as to ascertain the structure of the embryo; but he is not thereby prevented from referring the plant to its proper place, provided he can find out the structure of some other part-say its stem, or the arrangement of the veins of its leaves. If the venation of the leaf is netted, he concludes that the plant proceeded from a seed with two cotyledons, and was exogenous. Associations of character, such as we have described in the chapter on the Forms of Plants, are all important, not only in the examination of living, but of fossil plants. Fortunately the structure, whether exogenous or endogenous, can be detected in most fossil plants, and thus we have a key to explain other arrangements which must have been associated with it, and this holds true, whether we have the whole stem or merely a fragment. In most cases we have only a part, but when we do meet with an entire trunk, as of Mantellia nidiformis in the petrified forest of the Isle of Portland, we see at once that we have drawn legitimate conclusions.

The characteristic venation, whether netted or otherwise, obvious in the impressions of leaves met with in various geological strata, it is so well preserved, that botanists do not hesitate to refer them to one or other of the