every living thing upon the earth was destroyed. Furthermore, that the whole earth, at the beginning of each successive period, was stocked anew by special creation, with all its forms of life; and that these forms were everywhere impressed with the typecharacters peculiar to the respective epochs. Even after it became known that in numerous instances species and genera continued their existence from one period to another, it was still held that these were extra-limitary forms, and that their existence did not affect the exclusive character of the types of those animals and plants which were ordained to bear the chronological impress.

Accepting such a scheme of creation as this, it was natural to suppose that the types of animal and vegetable life which characterized each of the geological periods should be universal in its distribution, and strictly confined to the period for which it was specially created.

Although the doctrine of evolution is now accepted by every working naturalist, this idea of a successive series of narrow chronological horizons of universal extent, each characterized by its own peculiar types of organic forms, which are everywhere the same, and none of which exist in any other horizon, prevails to almost as great an extent as before. The later naturalists, it is true, based their views of this assumed constancy, not upon the idea of special creation and universal distribution in each period, as their predecessors did, but upon that of a progressive evolution, by distinct and world-wide steps, from pre-existing forms. The views which were held by the older naturalists were the result of a rational deduction from their own premises; but that similar views should be held by the naturalists of to-day is certainly unphilosophical. In accordance with the old views little opportunity was given for the variation of types, because, as they believed, all the species in which those types were expressed were sure to be extinguished at the close of each period, and they were to be succeeded by a newly-created series.

To the modern naturalist, a belief in the universal distribution, and narrow and rigidly restricted chronological range of organic types which characterize each successive epoch, implies that evolution has occurred in all instances in exactly the same mathematical ratio; for animal as well as vegetable forms; for aqueous as well as for terrestrial life; for the life of fresh waters as well as that of the seas; and under every environing condition of climate and of geological change. It implies the existence of some unknown and unexplainable law which, at the close of each epoch, required the utter and speedy extinction of exactly such types as had specially characterized those epochs, even if the physical conditions under which they had formerly existed had continued the same. That such ideas do prevail among paleontologists at the present time one has abundant proof in their published writings.

In Europe it was found that during the successive geological epochs certain types of plants and vertebrate and invertebrate animals all lived simultaneously; and the actual and relative rate of progress of evolution of the types in each of these great biological divisions, seeming to be a natural one, was regarded as under the influence of some cosmical law which necessarily made that rate uniform for the whole earth. When, therefore, even a single type, whether of plants or vertebrate or invertebrate animals, such as is known to characterize any European group of strata, has been found in any other part of the earth, it has been customary to hold that the animal or plant, as the case might be. which is represented by that type, existed simultaneously with its European congeners. Although the folly of relying upon such slender evidence has again and again been shown, it is not uncommon to see it presented in important paleontological publications with all the force that such words as "certainly," "undoubtedly," "unquestionably," &c., can give it.

I have made the foregoing statements, first, to call attention to the existence of the erroneous views which I have indicated; and, secondly, that they may serve as a suggestion of the reason

why they have obtained a foothold.

I am confident that if the

geological scheme had yet to be devised upon the basis of the advanced knowledge which naturalists have now acquired, it would be free from the defects which I have mentioned. In fact, it seems that these defects are due to the erroneous biological views which naturalists formerly entertained; and that they have remained solely because it is so difficult for men to free their minds from impressions which have once become firmly fixed, even after their fallacy has become apparent.

These errors have by no means escaped the attention of leading naturalists; and several years ago Prof. Huxley proposed the term "homotaxis" to express the existence of close biological relationship between formations in different parts of the world respectively, which might not, or could not, have been contemporaneously deposited. In using this term instead of " "equivalent," synchronous," &c., as has usually been done in relation to formations in separate regions which contain closely similar faunas or floras, one does not thus commit himself to any opinion as to the actual geological age of such formations, but only to the fact that the forms of life were similar when and where those formations were respectively deposited. Professor Huxley's idea may be represented graphically by superimposing upon the diagram which I have suggested a complementary series of lines, much as isothermal lines are superimposed upon a map with its lines of latitude. But to express the present state of our knowledge, these complementary or isotaxial lines must be sadly broken and fragmentary.

This idea of homotaxy necessarily has reference to some acknowledged standard of the order in which the geological formations have been deposited; and in using the term I shall of course have reference to that which is in general use, which is practically the European standard.

Various authors have shown, not only that many formations have been found in different parts of the world to be homotaxi

ally related to each other by their respective faunas and floras which certainly were not contemporaneously deposited, but also that many foreign formations contain faunas which respectively embrace homotaxial representatives of two or more European formations. After I had selected the subject, and written out the greater part of these remarks, the address of Mr. W. T. Blanford and the article of Mr. J. Starkie Gardner, read before the British Association for the Advancement of Science, at Montreal, reached my hands. I find from a perusal of them that both of those gentlemen have so far anticipated much which I intended to say that I cordially recommend my hearers to read those productions. Both of them, especially that of Mr. Blanford, record some startling exceptions to the generally received rule that formations homotaxially related were of contemporaneous origin. I shall have occasion to refer to some of the cases of this character which they have mentioned, and I shall also cite other instances which have come under my own observation. First, I shall mention instances where there is apparent reversion of the chronological order of the formations, and afterward those in which a commingling in one formation of the characteristic types of two or more epochs occur.

Mr. Blanford, in his address, cites a considerable number of instances where the order of occurrence of faunal and floral types, according to the accepted chronological scale, is reversed. One of these instances occurs at the famous Pikermi beds, near the ancient city of Athens. These beds contain a rich mammalian fauna which is so characteristically Miocene that the French committee of the International Congress of Geologists specially mention it as of that age. Some of the species of the Grecian locality referred to are identical with those of some of the fully recognized Miocene strata of other parts of Europe. Now, Professor Gaudry found in the lowest of these Grecian beds which bear Miocene vertebrates several species of well-known Pliocene mollusca, and he also found that this bed in turn rests upon a marine bed of undoubted Pliocene age."

A similar condition of things occurs among the Tertiary deposits along the southern base of the Himalayas in India, in what are known as the Siwalik beds. These beds contain a mammalian fauna which European paleontologists have unhesitatingly referred to the Miocene; but the geologists of the Indian survey have shown that they have many thousand feet of Miocene strata beneath them; and upon other grounds, also, they show that they cannot be of earlier age than the Pliocene.

Perhaps one of the most remarkable instances of the apparent reversion of the chronological order of the formations, as it is known in Europe, occurs in the great series of strata in India which is known as the Gondwána System. Mr. Blanford, in his address, gives an account of this remarkable case in detail. Certain of the beds of this system of formations contain a fauna which paleontologists agree in classifying as Triassic. These Triassic beds are found overlying beds which contain a Rhætic flora, or one which has its homotaxial representative in Europe between the Jurassic and Triassic; and, these Rhætic beds are found to overlie those which contain a flora that paleobotanists refer with confidence to the Jurassic period. In the other cases mentioned, there is a reversion of two homotaxial epochs; but in this Gondwana System the reversion embraces three of them. That is, the order of all the three is reversed, so that the ascending order in India is the same as the descending order in Europe.

Again, it has been shown by experienced geologists that in Australia there are beds which bear a flora that paleobotanists declare to be typically Jurassic, and which are interstratified with marine beds that bear an abundance of characteristic Lower Carboniferous molluscan species. And, furthermore, that these beds are overlaid by a fresh-water formation which has been referred with confidence to the Permian period.

Coming to our own country, the most remarkable case of the reversion of the order in which the faunal and floral types are