STUDY X. DAY III.—THE HABITATION OF LIFE. "Thou, O Spirit, that dost prefer, Before all temples, the upright heart and pure, I may assert eternal Providence, Paradise Lost. By sacred geology we understand that the formation of the earth was by the Almighty. He did not labour as an artificer who shapes every work by handicraft. We do not conceive that every species of rhinoceros, and every species of hyæna, or the long succession of forms from earliest to present time, was separately constructed out of the dust. Nor did God create by intellectual or physical exercise, such as we are capable of, but by means of incomprehensible operations, defined as natural order or law, He furnished space as the star-domed city of the great King; and now, through every star, through every grass-blade, but most through every living soul, beams the glory of an ever-present God ;-natural law being the formula of Divine action, and all dynamic phenomena the multiform revelation of the Omniscient and Omnipresent. By various orders of experience we may imagine humanwise the creative process. The passage of invisibles into visibles, as gas into light; the coming of the unseen vapour of water into the seen; are one step. We may think of germs growing into animals; of plants, great or small, developing in such minute progression that at no moment can it be said, The Creative Process. 183 "now the seed ceases, now the tree exists." We then observe that the origin of plants, animals, men, separated by wide intervals of time, is analogous to epochs in the formation of stars and planets. The earth may so change in the course of hundreds of thousands of years that none of the present forms of life shall exist. In other starry worlds have been, are, and will be lifeless ages, living durations, death periods. Within our intellectual conceptions we may hasten or retard the operation, show the vast reach of organic phenomena, render them intelligible, and obtain as clear a view of creation as we can of evolution; indeed, evolution, rightly understood, is creation. We may reverently regard the production now of every child, and flower, and tree, as a special creation : for the perpetual origination of countless individuals throughout the world, from hour to hour, is to the devout mind the more miraculous because so ordinary. Thought may take another turn: a straight line and a circle are not much alike-let the straight line be continued as a figure of infinity, and the circle be conceived vast as the universe. The one encloses a space; the other, though continued for ever, will not enclose a space. The one is limited, the other may be unlimited; but if the straight line be bent so slightly that no eye-no, not even aided by a rule -can appreciate it, you may get an immensely elongated form; and, if you go on, may acquire the peculiar properties and special equations of the hyperbola, parabola, ellipse, circle. The first and last, being quite opposite, are nevertheless made members of a series which you produce by insensible modifications. Such a mode of representation has been used to figure evolution; it may well and fairly be used as a symbol of that line and universe which He stretched and fashioned who went forth, by His will and power, to make all things in continuance. In continuance, for no one supposes that the oak, ready formed within the acorn, lies there in miniature. The oak is quite as much in the earth and air, not really in any one, but formed from all. In like manner, when the eye was created, the means may have been the action of light on a suitable sensitive surface; then this eye being brought into due relation with external objects, there would be visual perception. We may also picture to ourselves the forms of sense and the forms of thought, being created and devoloped in us, as the stem, branches, and foliage of the oak, are evolved from the acorn. It matters little what name we give to the process; the great desire of our age is for a doctrine which shall arrange our knowledge, guide our researches, shape our lives, so that right conduct shall be the result of true faith. Scientific geology treats of what materials the earth is composed, and in what manner they are arranged. It reveals that the earth, some long time ago, was in a viscous or even perfectly liquid state. Cooling rapidly at the surface, the crust became denser than the liquid below; and, when broken by pressure from within, portions sank down, and solidification began on the newly exposed liquid surface. From volcanic phenomena we learn that at no very great depth under the surface, there may be portions of the originally liquid mass at temperatures equivalent to red, or even white heat, but under great pressure. Sir William Thomson has shown, by means of arguments on the rate of precession, and on the amount of land-tide, that the whole mass of the earth is now more rigid than if it were glass throughout, nearly as rigid as a solid mass of steel. Scientific geology, not limited to the mineral kingdom, nor to the various rocks and soils, relates the history of animals and plants; investigates all the changes which have taken place in the former state of the earth's surface and interior. Science, thus ascertaining the manner and means by which the works of Nature are wrought, is beneficent priestess of the physical universe, and we reverently receive her instructions. She describes and fairly well maps out the nearer portion of the pathway on which our earth has travelled, her varied period of existence as a revolving globe, the production of rocks, the gathering of seas, the depths out of which dry land was raised, and the emptiness of land and sea until both became many-chambered habitations of life. It is proved that man had a beginning, that the animals had a beginning, that the earth's surface was rearranged again and again. Mountains were formed, raised, worn down, or sunk; valleys have been excavated, filled up, and again dug out; sea became dry land, land became sea; yet, throughout all revolutions and the accompanying vicissitudes of climate, animal and vegetable life was sustained-a continual modification fitting it for the different ages and stages of the world. A close analogy is shown to exist between extinct and recent species, and the continuance of the same organic laws is thus evidenced: ancient lakes in the Upper Miocene had round their borders belts of poplars and willows and shrubs. Leaves resembling those of the tamarind, with a ripe seed-vessel, have been found; and, on the same slab, a winged ant. We learn from this that the seed was ripened in summer, at which season alone ants have their wings fully developed and make their flight. In venturing upon a short sketch of chemical geology, or of what may be termed the cosmogenetic era in the history of our globe; and then explaining some of the phenomena of the great changes from that early period down to the present time; principles, rather than details of chemical action, will be dealt with. Exact knowledge shows that mere fire and water are not the only great agents; the geologist must take into consideration the effects which are wrought by chemical action, heat, light, electricity, mechanical force. It is known that mechanical force may be converted, directly or indirectly, not only into heat, but into chemical action in the metamorphic alteration of rock masses. The Plutonic, Neptunic, Quiescent, Cataclysmic schools of thought, reveal principles which have had a share in Nature's operations; and an independent observer finds that the same identical phenomena are at times the result of agencies totally different from those which at other times produced them. For example: Take crystallised silica, or quartz; it appears— As an igneous product in recent volcanic lavas; As an aqueous product, by crystallisation and deposition from solution; As a gasolytic product, in tubes from deposition of its compounds with fluorine. Sulphur is seen As an igneous product from volcanoes; In applying chemical principles in explanation of the changes wrought in our globe, we shall not touch upon the asserted early gasiform condition as a nebula in space, nor inquire whether the elements then were in a state of chemical indifference to one another, but deal with the earth in its heated condition of complete liquidity. There would be bodies of two different characters-solid and gasiform; these, by their situation and rotation, would bring about the formation of a molten sphere surrounded by an intensely heated gasiform atmosphere. The affinity of bodies would be different, and their mutual chemical reactions vary considerably, from what takes place at ordinary temperatures; so that our conclusions, in great part hypothetical, are as follows: The molten substances and their atmosphere would obey the laws of gravity; and arrange themselves in strata, or zones, according to their respective density. The molten mass would arrange into three grand zones, probably with sub-zones: i. An external crust of highly acid silicates, and probably much free quartz; the bases of silicates being chiefly alumina and potash, with some soda, lime, magnesia, etc. ii. A zone of silicates of more basic character and greater density; the bases being lime, magnesia, alumina, oxide of iron, soda, with minor quantities of potash and other substances. iii. A far denser nucleus, containing most of the densest metallic elements; in part, at least, combined with sulphur, arsenic, etc.1 These zones, formed in the earth, would be of somewhat stable character; those in the atmosphere the reverse; but, at first, the atmosphere, next the earth, would be composed of a dense vapour of compounds volatile only at high temperature-chloride of sodium, probably, one of the most prominent. Above this, carbonic acid; then oxygen and nitrogen; vapour of water still higher. Afterwards, this 'See Lecture, in Journal of the Chemical Society, 20th February, 1868, by David Forbes. |