Part 4

In the earliest vertebrate period, namely, the Silurian, our author shews that the fishes were homologically symmetrical in their organization, as exhibited in the Placoids. In the second great Ichthyic period, that of the Old Red Sandstone, he finds the first example in the class of fishes of _monstrosity, by displacement of parts_. In all the Ganoids of the period, there is the same departure from symmetry as would take place in man if his neck was annihilated, and the arms stuck to the back of the head. In the _Coccosteus_ and _Pterichthys_ of the same period, he finds the first example of _degradation through defect_, the former resembling a human monster without hands, and the latter one without feet. After ages and centuries have passed away, and then after the termination of the Palæozoic period, a change takes place in the formation of the fish tail. “Other ages and centuries pass away, during which the reptile class attains to its fullest development in point of size, organization, and number; and then, after the times of the cretaceous deposits have begun, we find yet another remarkable monstrosity of displacement introduced among all the fishes of one very numerous order, and among no inconsiderable proportion of the fishes of another. In the newly-introduced Ctenoids (_Acanthopterygii_,) and in those families of the Cycloids which Cuvier erected into the order _Malacopterygii sub-brachiati_, the hinder limbs are brought forward and stuck on to the base of the previously misplaced fore limbs. All the four limbs, by a strange monstrosity of displacement, are crowded into the place of the extinguished neck. And such, in the present day, is the prevalent type among fishes. Monstrosity through _defect_ is also found to increase; so that the snake-like _apoda_, or feet-wanting fishes, form a numerous order, some of whose genera are devoid, as in the common eels and the congers, of only the hinder limbs, while in others, as in the genera _Muræna_ and _Synbranchus_, both hinder and fore-limbs are wanting.” From these and other facts, our author concludes that as in existing fishes we find many more proofs of the monstrosity, both from displacement and defect of parts, than in all the other three classes of the vertebrata, and as these monstrosities did not appear early, but late, “the progress of the race as a whole, though it still retains not a few of the higher forms, has been a progress not of development from the low to the high, but of degradation from the high to the low.” An extreme example of the degradation of distortion, superadded to that of displacement, may be seen in the flounder, plaice, halibut, or turbot,—fishes of a family of which there is no trace in the earlier periods. The creature is twisted half round and laid on its side. The tail, too, is horizontal. Half the features of its head are twisted to one side, and the other half to the other, while its wry mouth is in keeping with its squint eyes. One jaw is straight, and the other like a bow; and while one contains from _four_ to _six_ teeth, the other contains from _thirty_ to _thirty-five_.

Aided by facts like these, an ingenious theorist might, as our author remarks, “get up as unexceptionable a theory of degradation as of development.” But however this may be, the principle of degradation actually exists, and “the history of its progress in creation bears directly against the assumption that the earlier vertebrata were of a lower type than the vertebrata of the same Ichthyic class which exist now.”

In his next and _tenth_ chapter, our author controverts with his usual power the argument in favor of the development hypothesis, drawn from the predominance of the Brachiopods among the Silurian Molluscs. The existence of the highly organized Cephalopods, in the same formation, not only neutralizes this argument, but authorizes the conclusion that an animal of a very high order of organization existed in the earliest formation. It is of no consequence whether the Cephalopods, or the Brachiopods were most numerous. Had there been only one cuttle fish in the Silurian seas, and a million of Brachiopods, the fact would equally have overturned the development system.

In the same chapter, Mr. Miller treats of the geological history of the Fossil flora, which has been pressed into the service of the development hypothesis. On the authority of Adolphe Brongniart, it was maintained that, previous to the age of the Lias, “Nature had failed to achieve a tree—and that the rich vegetation of the Coal Measures had been exclusively composed of magnificent immaturities of the vegetable kingdom, of gigantic ferns and club mosses, that attained to the size of forest trees, and of thickets of the swamp-loving horse-tail family of plants.” True exogenous trees, however, do exist of vast size, and in great numbers, in all the coal-fields of our own country, as has been proved by Mr. Miller. Nay, he himself discovered in the Old Red Sandstone, _Lignite_, which is proved to have formed part of a true gymnospermous tree, represented by the pines of Europe and America, or more probably, as Mr. Miller believes, by the Araucarians of Chili and New Zealand. This important discovery is pregnant with instruction. The ancient Conifer must have waved its green foliage over dry land, and it is not probable that it was the only tree in the primeval forest. “The ship carpenter,” as our author observes, “might have hopefully taken axe in hand to explore the woods for some such stately pine as the one described by Milton,—

‘Hewn on Norwegian hills, to be the mast Of some great admiral.’”

Viewing this _olive leaf_ of the Old Red Sandstone as not at all devoid of poetry, our author invites us to a voyage from the latest formation up to the first zone of the Silurian formation,—thus passing from ancient to still more ancient scenes of being, and finding, as at the commencement of our voyage, a graceful intermixture of land and water, continent, river, and sea.

But though the existence of a true Placoid, a real vertebrated fish, in the Cambrian limestone of Bala, and of true wood at the base of the Old Red Sandstone, are utterly incompatible with the development hypothesis, its supporters, thus driven to the wall, may take shelter under the vague and unquestioned truth that the lower plants and animals preceded the higher, and that the order of creation was fish, reptiles, birds, mammalia, quadrumana, and man. From this resource, too, our author has cut off his opponents, and proceeds to show that such an order of creation, “at once wonderful and beautiful,” does not afford even the slightest presumption in favor of the hypothesis which it is adduced to support.

This argument is carried on in a popular and amusing dialogue in the _eleventh_ chapter. Mr. Miller shows, in the clearest manner, that “superposition is not parental relation,” or that an organism lying above another gives us no ground for believing that the lower organism was the parent of the higher. The theorist, however, looks only at those phases of truth which are in unison with his own views; and, when truth presents no such favorable aspect, he finally wraps himself up in the folds of ignorance and ambiguity—the winding-sheet of error refuted and exposed. We have not yet penetrated, says he, in feeble accents, to the formations which represent the dawn of being, and the simplest organism may yet be detected beneath the lowest fossiliferous rocks. This undoubtedly _may be_, and Sir Charles Lyell and Mr. Leonard Horner are of opinion that such rocks may yet be discovered; while Sir Roderick Murchison and Professor Sedgwick and Mr. Miller are of an opposite opinion. But even were such rocks discovered to-morrow, it would not follow that their organisms gave the least support to the development hypothesis. In the year 1837, when fishes were not discovered in the Upper Silurian rocks, the theorist would have rightly predicted the existence of lower fossiliferous beds; but when they are discovered, and their fossils examined, they furnish the strongest argument that could be desired against the theory they were expected to sustain. This fact, no doubt, is so far in favor of the supposition that there may be still lower fossil-bearing strata; but, as Mr. Miller observes, “The pyramid of organized existence, as it ascends into the by-past eternity, inclines sensibly towards its apex,—that apex of ‘_beginning_’ on which, on far other than geological grounds, it is our privilege to believe. The broad base of the superstructure planted on the existing scene stretches across the entire scale on life, animal and vegetable; but it contracts as it rises into the past;—man,—the quadrumana,—the quadrupedal man,—the bird and the reptile are each in succession struck from off its breadth, till we at length see it with the vertebrata, represented by only the fish, narrowing as it were to a point; and though the clouds of the upper region may hide its apex, we infer, from the declination of its sides, that it cannot penetrate much farther into the profound.”

In our author’s next chapter, the _twelfth_ of the series, he proceeds to examine the “Lamarckian hypothesis of the origin of plants, and its consequences.”

In his _thirteenth_ chapter, on “The two Floras, marine and terrestrial,” he has shown that all our experience is opposed to the opinion, that the one has been transmuted into the other. If the marine had been converted into terrestrial vegetation, we ought to have, in the Lake of Stennis, for example, plants of an intermediate character between the algæ of the sea, and the monocotyledons of the lake. But no such transition-plants are found. The algæ, as our author observes, become dwarfish and ill-developed. They cease to exist as the water becomes fresher, “until at length we find, instead of the brown, rootless, flowerless fucoids and confervæ of the ocean, the green, rooted, flowering flags, rushes, and aquatic grasses of the fresh water. Many thousands of years have failed to originate a single intermediate plant.” The same conclusion may be drawn from the character of the vegetation along the extensive shores of Britain and Ireland. No botanist has ever found a single plant in the transition state.

The _fourteenth_ chapter of the “Footprints” will be perused with great interest by the general reader. It is a powerful and argumentative exposure of the development hypothesis, and of the manner in which the subject has been treated in the “Vestiges.” Whether we consider it in its nature, in its history, or in the character of the intellects with whom it originated, or by whom it has been received and supported, Mr. Miller has shown that it has nothing to recommend it. It existed as a wild dream before Geology had any being as a science. It was broached more than a century ago by De Maillet, who knew nothing of the geology even of his day. In a translation of his Telhamed, published in 1750, Mr. Miller finds very nearly the same account given of the origin of plants and animals, as that in the “Vestiges,” and in which the sea is described as that “great and fruitful womb of nature, in which organization and life first begin.” Lamarck, though a skilful botanist and conchologist, was unacquainted with geology; and as he first published his development hypothesis in 1802, (an hypothesis identical with that of the “Vestiges,”) it is probable that he was not then a very skilful zoologist. Nor has Professor Oken any higher claims to geological acquirements. He confesses that he wrote the first edition of his work in _a kind of inspiration!_ and it is not difficult to estimate the intelligence of the inspiring idol that announced to the German sage that the globe was a vast crystal, a little flawed in the facets, and that quartz, feldspar, and mica, the three constituents of granite, were the hail-drops of heavy showers of stone that fell into the original ocean, and accumulated into rocks at the bottom!

Such is the unscientific parentage of the theories promulgated in the “Vestiges.” But the author of this work appeals in the first instance to science. Astronomy, Geology, Botany, and Zoology are called upon to give evidence in his favor; but the astronomer, geologist, botanist, and the zoologist, all refuse him their testimony, deny his premises, and reject his results. “It is not,” as Mr. Miller happily observes, “the illiberal religionist that casts him off. It is the inductive philosopher.” Science addresses him in the language of the possessed: “The astronomer I know, and the geologist I know; but who are ye?” Thus left alone in a cloud of star-dust, or in brackish water between the marine and terrestrial flora, he “appeals from science to the want of it,” casts a stone at our Scientific Institutions, and demands a jury of “ordinary readers,” as the only “tribunal” by which “the new philosophy is to be truly and righteously judged.”

The last and _fifteenth_ chapter of Mr. Miller’s work, “On the Bearing of Final Causes on Geologic History,” if read with care and thought, will prove at once delightful and instructive. The principle of _final causes_, or the conditions of existence, affords a wide scope to our reason in Natural History, but especially in Geology. It becomes an interesting inquiry, if any reason can be assigned why at certain periods species began to exist, and became extinct after the lapse of lengthened periods of time, and why the higher classes of being succeeded the lower in the order of creation? The incompleteness of geological science, however, does not permit us to remove, for the present, the veil which hangs over this mysterious chronology; but our author is of opinion that in about a quarter of a century, in a favored locality like the British Islands, geological history “will assume a very extraordinary form.”

It is a singular fact, which will yet lead to singular results, that Cuvier’s arrangement of the four classes of vertebrate animals should exhibit the same order as that in which they are found in the strata of the earth. In the _fish_, the average proportion of the brain to the spinal cord is only as 2 to 1. In the _reptile_, the ratio is 2½ to 1. In the _bird_, it is as 3 to 1. In the _mammalia_, it is as 4 to 1; and in _man_, it is as 23 to 1. No less remarkable is the fœtal progress of the human brain. It first becomes a brain resembling that of a fish; then it grows into the form of that of a reptile; then into that of a bird; then into that of a mammiferous quadruped, and finally it assumes the form of a human brain, “thus comprising in its fœtal progress an epitome of geological history, as if man were in himself a compendium of all animated nature, and of kin to every creature that lives.”

With these considerations, Mr. Miller has brought his subject to the point at which Science in its onward progress now stands. It is to embryology we are in future to look for further information upon the most intimate relations which exist between all organized beings. We may fairly entertain the hope that the time is not far when we shall not only fully understand the Plan of Creation, but even lift some corner of the veil which has hitherto prevented us from forming adequate ideas of the first introduction of animal and vegetable life upon earth, and of the changes which both kingdoms have undergone in the succession of geological ages.

L. AGASSIZ.

CAMBRIDGE, _September, 1850_.

CONTENTS

PAGE

STROMNESS AND ITS ASTEROLEPIS.—THE LAKE OF STENNIS 21

THE DEVELOPMENT HYPOTHESIS, AND ITS CONSEQUENCES 37

THE RECENT HISTORY OF THE ASTEROLEPIS.—ITS FAMILY 48

CEREBRAL DEVELOPMENT OF THE EARLIER VERTEBRATA.—ITS APPARENT PRINCIPLE 62

THE ASTEROLEPIS.—ITS STRUCTURE, BULK, AND ASPECT 94

FISHES OF THE SILURIAN ROCKS, UPPER AND LOWER.—THEIR RECENT HISTORY, ORDER, AND SIZE 130

HIGH STANDING OF THE PLACOIDS.—OBJECTIONS CONSIDERED 147

THE PLACOID BRAIN.—EMBRYONIC CHARACTERISTICS NOT NECESSARILY OF A LOW ORDER 160

THE PROGRESS OF DEGRADATION.—ITS HISTORY 181

EVIDENCE OF THE SILURIAN MOLLUSCS.—OF THE FOSSIL FLORA.—ANCIENT TREE 205

SUPERPOSITION NOT PARENTAL RELATION.—THE BEGINNINGS OF LIFE 230

LAMARCKIAN HYPOTHESIS OF THE ORIGIN OF PLANTS.—ITS CONSEQUENCES 243

THE TWO FLORAS, MARINE AND TERRESTRIAL.—BEARING OF THE EXPERIENCE ARGUMENT 262

THE DEVELOPMENT HYPOTHESIS IN ITS EMBRYONIC STATE.—OLDER THAN ITS ALLEGED FOUNDATIONS 277

FINAL CAUSES—THEIR BEARING ON GEOLOGIC HISTORY—CONCLUSION 303

LIST OF WOOD-CUTS

PAGE

1. Internal ridge of hyoid plate of _Asterolepis_ 31

2. Shagreen of _Raja clavata_:—of _Sphagodus_ 54

3. Scales of _Acanthodes sulcatus_:—shagreen of _Scyllium stellare_ 55

4. Scales of _Cheiracanthus microlepidotus_:—shagreen of _Spinax Acanthias_ 56

5. Section of shagreen of _Scyllium stellare_:—of scales of _Cheiracanthus microlepidotus_ 56

6. Scales of _Osteolepis microlepidotus_:—of an undescribed species of _Glyptolepis_ 57

7. Osseous points Of Placoid Cranium 65

8. Osseous centrum of _Spinax Acanthias_:—of _Raja clavata_ 67

9. Portions of caudal fin of _Cheiracanthus_:—of _Cheirolepis_ 69

10. Upper surface of cranium of Cod 72

11. Cranial buckler of _Coccosteus_ 74

12. Cranial buckler of _Osteolepis_ 75

13. Upper surface of head of _Osteolepis_ 77

14. Under surface of head of _Osteolepis_ 79

15. Head of _Osteolepis_, seen in profile 80

16. Cranial buckler of _Diplopterus_ 81

17. Ditto 82

18. Palatal dart-head, and group of palatal teeth, of _Dipterus_ 83

19. Cranial buckler of _Dipterus_ 85

20. Base of cranium of _Dipterus_ 86

21. Under jaw of _Dipterus_ 87

22. Longitudinal section of head of _Dipterus_ 88

23. Section of vertebral centrum of Thornback 92

24. Dermal tubercles of _Asterolepis_ 95

25. Scales of _Asterolepis_ 96

26. Portion of carved surface of scale 96

27. Cranial buckler of _Asterolepis_ 98

28. Inner surface of cranial buckler of _Asterolepis_ 99

29. Plates of cranial buckler of _Asterolepis_ 102

30. Portion of under jaw of _Asterolepis_ 103

31. Inner side of portion of under jaw of _Asterolepis_ 104

32. Portion of transverse section of reptile tooth of _Asterolepis_ 105

33. Section of jaw of _Asterolepis_ 106

34. Maxillary bone? 108

35. Inner surface of operculum of _Asterolepis_ 109

36. Hyoid plate 110

37. Nail-like bone of hyoid plate 111

38. Shoulder plate of _Asterolepis_ 112

39. Dermal bones of _Asterolepis_ 113

40. Internal bones of _Asterolepis_ 114

41. Ditto 115

42. Ischium of _Asterolepis_ 116

43. Joint of ray of Thornback:—of _Asterolepis_ 117

44. Coprolites of _Asterolepis_ 118

45. Hyoid plate of Thurso _Asterolepis_ 124

46. Hyoid plate of Russian _Asterolepis_ 127

47. Spine of _Spinax Acanthias_:—fragment of Onondago spine 143

48. Tail of _Spinax Acanthius_:—of _Ichthyosaurus tenuirostris_ 172

49. Port Jackson Shark (_Cestracion Phillippi_) 177

50. Tail of _Osteolepis_ 195

51. Tail of _Lepidosteus osseus_ 196

52. Tail of Perch 197

53. _Altingia excelsa_ (Norfolk-Island Pine) 212

54. Fucoids of the Lower Old Red Sandstone 216

55. Two species of Old Red Fucoids 217

56. Fern (?) of the Lower Old Red Sandstone 219

57. Lignite of the Lower Old Red Sandstone 221

58. Internal structure of lignite of Lower Old Red Sandstone 223

STROMNESS AND ITS ASTEROLEPIS. THE LAKE OF STENNIS.

When engaged in prosecuting the self-imposed task of examining in detail the various fossiliferous deposits of Scotland, in the hope of ultimately acquainting myself with them all, I extended my exploratory ramble, about two years ago, into the Mainland of Orkney, and resided for some time in the vicinity of Stromness.