Three solu

lead us into the error of imputing to such a law, impressed by the Creator on the developing organism, that which really belongs to external physical conditions, which, on their part, are following a law of their own. What is here meant may be illustrated by the facts that occur on the habitable surface of a planet suffering a gradual decline of heat. On such a surface a succession tions of it. of vegetable types might make its appearance, and, as these different types emerged or were eliminated, we might speak of the events as creations and extinctions, and therefore as the acts of God. Or, in the second place, we might refer them to an intrinsic force of development imparted to each germ, which reached in due season its maximum, and then declined and died out; and, comparing each type with its preceding and succeeding ones, the interrelation might be suggested to us of the operation of a controlling law. Or, in the third place, we might look to the external physical condition-the decline of heat-itself taking place at a determinate rate under a mathematical law, and drawing in its consequences the organic variations observed.

Now the first of these explanations in reality means the arbitrary and unchallengeable will of God, who calls into existence, and extinguishes according to his sovereign pleasure, whatever he pleases; the orderly progression we notice becoming an evidence that his volitions are not erratic, but are according to pure reason. The second implies that there has been impressed upon every germ a law of continuous organic variation-it might have been through the arbitrary fiat of God. The third implies that the successive types owe their appearance and elimination to a physical influence, which is itself varying under a strict mathematical necessity; for the law of cooling, which the circumstances force on our attention, is such a strict mathematical necessity.

If at this point we balance the probabilities of these Their relative three explanations, we shall perhaps find ourprobability. selves biassed toward the last, as physiologists have been, because of its rigorous scientific aspect, and should not be surprised to find it supported by an array of facts depending on the principle that the appearance of

new forms does not observe a certain inevitable order, or stand in a certain relation to time. From individual development it might seem as if the advancing procession of an organism is such that specific forms ever appear in a certain order one after another, and at certain intervals; but the fallacy of such a conclusion is apparent when we attend to the orderly procedure of the physical conditions to which the developing organism is exposed. The passing through a given form at a given epoch is due to the relation being to space and its conditions, Development not to time. And so in the life of the earth, if is in place, development were according to time, we should not in time. have an orderly succession of grades as the earth grew older, and in all localities, at a given moment, the contemporary organisms would be similar; but if it were according to space, that rigorous procedure would not occur; in its stead we should have a broken series, the affiliation being dependent on the secularly continuous variation of the physical condition.

Now this was discovered to be the case. For instance, throughout the northern hemisphere, during the Tertiary period, an extinct placental Fauna was contemporaneous with an extinct marsupial Fauna in Australia. If the development was proceeding according to time, by an innate nisus, and not according to external influences, the types for the same epoch in the two hemispheres should be the same; if under external influences, irrespective of time, they should be, as they were found to be, different.

If true-going clocks, which owe their motion to their own internal mechanism, were started in all countries of the earth at the same instant, they would strike their successive hours simultaneously. But sun-dials, which owe their indications to an exterior cause, would in different longitudes tell different times, or, when the needful light was absent, their shadows would altogether fail.

As to the vegetable kingdom, the principles that hold for the animal again apply. At a very early period, even before the deposit of the coal, all the distinct forms of vegetable tissue were in existence, and nothing to prevent, so far as time was concerned, their being united together all over the world into similar structural combinations.

And, in truth, as the botany of the Coal period proves, there was a far more extensive sameness than we see at present, simply because the distribution of heat was more uniform and climates were less marked. But from this point the diversity of form in climate distribution becomes more and more conspicuous, though we must descend, perhaps, as late as the Wealden before we discover any flowering plants, except Gymnosperms, as Conifers and Cycads. All this is what might be expected on the doctrine of external influence, but not on the doctrine of an innate and interior developmental force.

If, at this stage, attention is once again turned to the animal kingdom, we find our opinion confirmed. The diminution of carbonic acid in the atmosphere, the deposit of coal in the earth, the precipitation of carbonate of lime in the sea, the disengagement of an increased quantity of oxygen in the air, and the reduction of atmospheric pressure-different effects contemporaneously occurring-were soon followed by the consequence which they made possible—the appearance of hot-blooded mammals. Perhaps Cold and hot- those first arising might, like our hibernates, lead a sluggish existence, with imperfect respiration; but, as the media improved and the temperature declined, more vigorous forms of life emerged, though we have probably to descend to the Tertiary epoch before we meet with birds, which of all animals have the most energetic respiration, and possess the highest heat.

mals.

As with the atmosphere, so with the sea. Variations in The organisms its composition must control the organisms it of the sea. contains. With its saline constituents its life must change. Before the sunlight had removed from the atmosphere so much of its carbonic acid, decomposing it through the agency of plants, the weight of carbonate of lime held in solution by the highly carbonated water was far greater than was subsequently possible, and the occurrence of limestone became a necessary event. With such a disturbance in the composition of the sea-water, its inhabiting organisms were necessarily disturbed. And so again, subsequently, when the solar heat began to preponderate on the surface over the subsiding interior heat,

the constitution of the sea-water, as respects its salinity, was altered through difference of evaporation in different latitudes, an effect inevitably making a profound impression on marine animal life.

transmission.

We

Supported by the facts that have been mentioned respecting the later fossils of Australia and Brazil, Nature of and their analogy to forms now existing in those hereditary countries, much stress was laid on the hereditary transmission of structure, and hence the inference was drawn that such examples are of a mixed nature, depending in part on external agency, in part on an interior developmental force. From marsupial animals, marsupials will issue; from placental ones, those that are placental. But here, perhaps, an illustration drawn from the inorganic kingdom may not be without interest and use. Two pieces of carbonate of lime may be rolling among the pebbles at the bottom of a brook, one perpetually splitting into rhomboids, the other into arragonitic prisms. The fragments differ from one another not only thus in their crystalline form, but in their physical qualities, as density and hardness, and in their optical qualities also. might say that the calc-spar crystals gave birth to calcspar crystals, and the arragonitic to arragonite; we might admit that there is an interior propensity, an intrinsic tendency to produce that result, just as we say that there is a tendency in the marsupial to engender a marsupial; but if, in our illustration, we look for the cause of that cause, we find it in a physical impression long antecedently made, that the carbonate of lime, crystallizing at 212° Fahr., produces arragonite, and, at a lower temperature, calc spar; and that the physical impression thus accomplished, though it may have been thousands of years ago, was never cast off, but perpetually manifested itself in all the future history of the two samples. That which we sometimes speak of as hereditary transmission, and refer to an interior property, peculiarity, or force, may be nothing more than the manifestation of a physical impression long antecedently made.

In the last place, the idea of an intrinsic force of development is in connexion with time and a progression, and only comes into prominence when we examine a

limited portion or number of the things under consideration. The earth, though very beautiful, is very far from The broken being perfect. The plants and animals we sea organic chain. are only the wrecks of a broken series, an incomplete, and, therefore, unworthy testimonial of the Almighty power. We should judge very inadequately of some great author if only here and there a fragmentary paragraph of his work remained; and so, in the book of organization, we must combine what is left with what we can recover from past ages and buried strata before we can rise to a comprehension of the grand argument, and intelligibly grasp the whole work.

Enormous

age of the earth.

It

Of that book it is immaterial to what page we turn. tells us of effects of such magnitude as imply prodigiously long periods of time for their accomplishment. Its moments look to us as if they were eternities. What shall we say when we read in it that there are fossiliferous rocks which have been slowly raised ten thousand feet above the level of the sea so lately as since the commencement of the Tertiary times; that the Purbeck beds of the upper oolite are in themselves the memorials of an enormous lapse of time; that, since a forest in a thousand years can scarce produce more than two or three feet of vegetable soil, each dirt-bed is the work of hundreds of centuries. What shall we say when it tells us that the delta of the Mississippi could only be formed in many tens of thousands of years, and yet that is only as yesterday when compared with the date of the inland terraces; that the recession of the Falls of Niagara from Queenstown to the present site consumed thirty thousand years; that if the depression of the carboniferous strata of Nova Scotia took place at the rate of four feet in a century, there were demanded 375,000 years for its completionsuch a movement in the upward direction would have raised Mont Blanc; that it would take as great a river as the Mississippi two millions of years to convey into the Gulf of Mexico as much sediment as is found in those strata. Such statements may appear to us, who with difficulty shake off the absurdities of the patristic chronology, wild and impossible to be maintained, and yet they are the conclusions that the most learned and profound