GIFT OF 
 MICHAEL REESE 
 
 EARTH 
 
 SCIENCES 
 LIBRARY 
 
UNIVERSITY 
 
THE 
 
 GEOLOGICAL EVIDENCES 
 
 OF 
 
 EVOLUTION. 
 
 BY 
 
 ANGELO HEILPRIN. 
 
 It 
 
 PROFESSOR OF INVERTEBRATE PALEONTOLOGY AT, AND CURATOR-IN-CH ARGK OF, 
 THE ACADEMY OF NATURAL SCIENCES OF PHILADELPHIA. 
 
 AUTHOR OF 
 
 "TOWN GEOLOGY: THE LESSON OF THE PHILADELPHIA ROCKS," "THE GEOGRAPHICAL 
 
 AND GEOLOGICAL DISTRIBUTION OF ANIMALS" (INTERNATIONAL 
 
 SCIENTIFIC SERIES), ETC. 
 
 PHILADELPHIA: 
 
 PUBLISHED BY THE AUTHOR. 
 
 ACADEMY OF NATURAL SCIENCES. 
 1888. 
 
SCIENCES 
 LIBRAE, 
 
 COPYRIGHT, 1888, BY A. HEILPRIN. 
 
TO MY DEAR PARENTS, 
 
 TO WHOSE LOVE FOR NATURE I OWE 
 
 WHAT LITTLE OF SCIENTIFIC KNOWLEDGE I POSSESS, 
 AND WHOSE KINDLY SYMPATHY WITH MY WORK 
 
 HAS BEEN THE SPUR TO MY LABORS, 
 THE FOLLOWING PAGES ARE AFFECTIONATELY INSCRIBED. 
 
 A. H. 
 
WHILE much has been done toward popular- 
 izing the subject of Evolution, whether in the way 
 of expounding the principles of the doctrine, or of 
 gathering in the proofs in favor of it, there has 
 not thus far appeared, to the knowledge of the 
 author, any collective or consecutive statement of 
 the evidence which geology and paleontology 
 present in support of organic transmutation. With 
 the view of partially filling this gap in the litera- 
 ture of Darwinism the author has prepared, at 
 the request of many of his friends, the following 
 
pages, which represent, somewhat broadened, the 
 substance of a Friday evening discourse delivered 
 at the Academy of Natural Sciences of Phila- 
 
 jf& ** v ' ' "'" -i *'-* 
 
 delphia. Brief though the statement is, it is 
 hoped that it may yet be of service to those to 
 whom the more specialized material is not 
 
 readily accessible. 
 
 A. H. 
 
 ACADEMY OF NATURAL SCIENCES, 
 
 Philadelphia, December, 1887. 
 
3 4^ 
 
 Of rm 'r 
 UNIVERSITY 
 
 THE GEOLOGICAL EVIDENCES 
 
 OF 
 
 EVOLUTION. 
 
 JUST fifty years ago this year were planted the 
 germs of a train of scientific speculation whose 
 development was destined to mark an epoch in 
 the history of science to work a most profound 
 revolution in the tendencies of modern thought. 
 It was then that Charles Darwin first conceived the 
 idea of investigating that mystery of mysteries, the 
 origin of species, and it was then that he laid the 
 foundation of that remarkable work which some 
 twenty years later was destined to convulse the sci- 
 entific world. Nearly thirty years have now elapsed 
 
2 THE GEOLOGICAL EVIDENCES 
 
 since the "Origin of Species" first saw the light of 
 day, and although in its infancy it met with but few 
 adherents to its general proposition that all existing 
 organic forms are but modifications of, or deriva- 
 tives from, allied or previously existing forms, it 
 numbers at the present day an equally small, or still 
 smaller, number of opponents. It may safely be 
 said that no broad scientific generalization, unless 
 possibly it be that of the Correlation of Forces, ever 
 met with such ready acceptance as did the doctrine 
 of evolution or transformism. It is not my purpose 
 to-night to discuss the status of evolution, which 
 has long since passed from the realm of pure and 
 simple theory, but to present to you such of the 
 more salient facts bearing upon its proof, drawn 
 from my own department of geology and paleontol- 
 ogy, as will permit you to understand why the 
 greater number of naturalists consider the doctrine 
 as firmly established to-day as is the Copernican 
 theory of planetary revolution, the theory of grav- 
 itation, or the undulatory theory of light. 
 
 Before entering into an analysis of this evidence, 
 
 i 
 
OF EVOLUTION. 
 
 it will be well to understand what is meant by the 
 term " evolution" as applied to organic beings. 
 There is much misconception on this point, arising 
 primarily from an erroneous interpretation of the 
 relations which the different animal and vegetable 
 organisms hold to one another. Evolution, in its 
 more common acceptation in the sense I propose 
 treating of it to-night signifies merely the evolving 
 or production of new organic forms from forms 
 more or less unlike themselves ; it recognizes as the 
 result of its action that all the varied animal and 
 vegetable forms now inhabiting or covering the 
 earth's surface are the descendants, through a long 
 series of modifications or transformations, of a lim- 
 ited number of ancient types whose ancestry lies 
 buried deep in the history of the world. As a 
 corollary of this, which might be termed material 
 evolution, we have an accompanying evolution of 
 the mind, habit, and consciousness, but these 
 important factors in sociology do not concern us 
 this evening. 
 
 One of the most popular fallacies connected with 
 
4 THE GEOLOGICAL EVIDENCES 
 
 evolution is the supposition that if all organic forms 
 are mere derivatives of one another, no matter how 
 unlike they may be, it follows that they occupy a 
 serial position with reference to each other; in other 
 words, it is conceived that if all the connecting forms 
 were discovered, they would build up a continuous 
 organic chain. Nothing could be further from 
 the truth ; evolution recognizes modification in the 
 most divergent directions, and the tree of life that 
 it restores is not a straight stem growing from a 
 continuous apical bud, but a stem, or possibly even 
 a limited number of stems, branching in varying 
 directions. The bird, which, in our conception of 
 structural organization, stands intermediate in rank 
 between the reptile and mammal, appears to be a 
 descendant of the former, the reptile, but the 
 mammal, which immediately follows the bird, has 
 little or no direct connection with it. One line 
 or the other is a side line, and there can be no 
 connection between the two except at their points 
 of divergence. 
 
 Granting the truth of the doctrine of evolution, 
 
OF EVOLUTION. 
 
 what is the nature of the proof that would be 
 required of the geologist to establish its validity ? 
 He would be required to show, in the first place, 
 that there has been a steady advance in the type 
 of structural organization from first to last not a 
 necessary elimination of forms of low degree, but 
 an overbalancing of these by forms of a more 
 complicated or higher grade of structure. Evo- 
 lution does not hold, as some opponents of the 
 theory would lead us to suppose, that the progres- 
 sive modification of individual organic forms 
 need be, or indeed has been, one of continuous 
 advance ; it recognizes merely a general advance 
 for the entire organic frame, while it admits of indi- 
 vidual retardation or degeneration. Its progress or 
 procession is the equivalent of the progress seen in 
 the development of civilization ; the united world 
 advances, whereas individual tribes or nations 
 remain at a standstill, or even degenerate and decay. 
 Such is precisely the history of the organic devel- 
 opment of our planet ; new and more complicated 
 organic types are being continually evolved, but 
 
6 THE GEOLOGICAL EVIDENCES 
 
 side by side with these forms we still meet with 
 those of a lower grade of organization, while still 
 others, belonging to the earlier periods of the 
 earth's history, have completely dropped out. 
 
 As a second proof of his position the geologist 
 would be compelled to show the lines along which 
 certain organic forms have developed ; to speak 
 more explicitly, he would be required to indi- 
 cate a number of transitional types intermediate 
 in their relations between forms otherwise appar- 
 ently far removed from one another. These 
 are the so-called " missing links." Furthermore, 
 these missing links must appear at definite geolo- 
 gical periods, and not promiscuously at all times 
 and places. This is practically the sum total of 
 the proof that would be required of the geologist, 
 and I believe that I shall be able during the course 
 of the evening to show to your entire satisfaction 
 that he can furnish this proof, and furnish it in a 
 most convincing manner. 
 
 I have placed before you a chart representing the 
 different geological periods, beginning with the 
 
OF EVOLUTION. 
 
 oldest at the bottom and ending with the newest on 
 top. I have so arranged it that each vertical inch 
 of its surface covers 2,000 feet thickness of deposit 
 belonging to each of the several periods of time, 
 the maxima of thickness occurring at any one part 
 of the earth's surface having been selected.* 
 You can thus determine for yourselves the rela- 
 tive values, as measured by the thickness of the 
 several deposits, of the different periods of time, 
 an important consideration in dealing with the life- 
 histories of animal groups. Now, when we seek to 
 investigate the life -histories of the different periods 
 indicated on this chart, we are immediately struck 
 by the very remarkable progression of the animal 
 forms distinctive of those periods. Instead of meet- 
 ing with a promiscuous association of animals of 
 lowest and highest organization, we find a gen- 
 eral advance in structural type from beginning to 
 end. It is true, we cannot in all cases indicate that 
 
 * In the following table the relative thicknesses are 
 expressed in feet, and the measure referred to in the text 
 has necessarily been omitted. 
 
GEOLOGICAL EVIDENCES 
 
 
 
 Epochs and Formations. 
 
 Faunal Characters. 
 
 
 
 POST-PLIOCENE. 
 Glacial Period. 
 
 Man. Mammalia principally of living 
 species. Mollusca exclusively recent. 
 
 ERTIAR^! 
 
 
 PLIOCENE, 3,000 feet. 
 
 Mammalia principally of recent genera 
 living species rare. Mollusca very 
 modern. 
 
 H 
 
 8 ' 
 
 o 
 
 
 MIOCENE, 4,000 ft. 
 OLIGOCENE, 8,000 ft. 
 
 Mammalia principally of living fam- 
 ilies ; extinct genera numerous ; spe- 
 cies all extinct. Mollusca largely of 
 recent species. 
 
 5 
 
 i 
 
 
 EOCENE, 10,000 ft. 
 
 Mammalia with numerous extinct fam- 
 ilies and orders; all the species and 
 most of the genera extinct. Modern 
 type Shell-Fish. 
 
 
 
 LARAMIE, 4,000 ft. 
 
 Passage Beds. 
 
 NDARY. 
 
 
 CRETACEOUS, 12,000 ft. 
 Chalk. 
 
 Dinosaurian (bird-like) Reptiles ; Pter- 
 odactyls (flying Reptiles) ; toothed 
 Birds ; earliest Snake ; bony Fishes ; 
 Crocodiles ; Turtles ; Ammonites. 
 
 
 
 03 
 
 Si 
 O 
 
 o 
 
 
 JURASSIC, 6,000 ft. 
 Oolite. 
 Lias. 
 
 Earliest Birds ; giant Reptiles (Ichthy- 
 osaurs, Dinosaurs, Pterodactyls) ; Am- 
 monites ; Clam-and Snail-Shells very 
 abundant ; decline of Brachiopods ; 
 Butterfly. 
 
 1 
 
 
 TRIAS, 5,000 ft. 
 New Red Sandstone. 
 
 First Mammalian (Marsupial) ; 2-gilled 
 Cephalopods (Cuttle-Fishes, Belem- 
 nites) ; reptilian Foot- Prints. 
 
 
 
 PERMIAN, 5,000 ft. 
 
 Earliest true Reptiles. 
 
 MARY. 
 
 
 CARBONIFEROUS, 
 26,000 ft. 
 Coal. 
 
 Earliest Amphibian (Labyrinthodont); 
 extinction of Trilobites ; first Cray- 
 fish ; Beetles ; Cockroaches ; Cent- 
 ipedes ; Spiders. 
 
 3 
 
 PH 
 
 8 ' 
 
 o 
 
 
 DEVONIAN, 18,000 ft. 
 Old Red Sandstone. 
 
 Cartilaginous and Ganoid Fishes; ear- 
 liest land (snail) and freshwater 
 Shells ; Shell-Fish abundant ; decline' 
 of Trilobites ; May-flies ; Crab. 
 
 l-s 
 
 & 
 
 
 SILURIAN, 33,000 ft. 
 
 Earliest Fish ; the first Air-Breathers 
 (Insect, Scorpion) ; Brachiopods and 
 4-gilled Cephalopods very abundant ; 
 Trilobites; Corals; Graptolites. 
 
 
 
 CAMBRIAN, 24,000 ft. 
 
 Trilobites ; Brachiopod Mollusks. 
 
 g 
 
 ' 
 
 ARCHAEAN, 30,000 ft. 
 Huronian. 
 Laurentian. 
 
 Eozoon (probably not a fossil.) 
 
 
 
 PRIMEVAL. 
 
 Non-sedimentary. 
 
OF EVOLUTION. 
 
 a type of higher or more complicated organization 
 invariably followed a lower type belonging to the 
 same group, but as a general rule we note that 
 there has been a steady advance in type structure. 
 What is the nature of this advance, or the essence 
 of the first required proof? 
 
 Looking at the animal kingdom broadly, and 
 without attempting to destroy the perspective by 
 inquiring into unnecessary details, we find that of 
 the two great divisions into which that kingdom is 
 divided, the backboned or vertebrate animals, like 
 the fish, reptile, amphibian, and quadruped, and 
 those without backbone, the Invertebrata, like the 
 coral, starfish, crab, etc., only the latter is rep- 
 resented in the earliest period, the Cambrian, 
 in which indisputable animal remains have been 
 found. Not a vestige of any of the higher forms 
 has here been met with. But let me warn 
 you against this non-appearance. It is by no 
 means impossible, or indeed unlikely, that back- 
 boned animals already lived during this period of 
 time, and that their remains will still some day be 
 
io THE GEOLOGICAL EVIDENCES 
 
 discovered. The fact, however, that the Cambrian 
 deposits have been so extensively studied, and that 
 no such remains have yet been found, renders it 
 more than probable that the animals of this class, 
 if they existed at all, existed in very small num- 
 bers ; and there can scarcely be a shadow of doubt 
 that their real development followed that of the 
 animals without backbone, whose remains are so 
 numerously scattered through the rocks. And let 
 me warn you further that the future finding of a few 
 vertebrate remains in the Cambrian deposits will be 
 no evidence against the doctrine of evolution not 
 until these remains will be found very much more 
 numerously than there is a prospect of ever find- 
 ing them. 
 
 In the period succeeding the Cambrian, the Silu- 
 rian, we find the first traces of backboned animals, 
 and what are they ? The lowest members of the 
 series, those which exhibit the least development of 
 the sense organs the fishes. These animals are 
 numerically insignificant during this era, and appear 
 only towards its close ; in the period following, 
 
OF EVOLUTION. 
 
 the Devonian, they become very abundant, so much 
 so that this period has been aptly designated the 
 "Age of Fishes." But neither here, nor in the 
 period preceding, the Silurian, has there ever been 
 found a vestige of an animal higher in the scale of 
 organization than a fish. In the rocks of the Car- 
 boniferous period do the first of the more highly 
 organized animals appear, but only in forms, as far 
 as it is possible to determine from our knowledge 
 of recent animal life, whose early existence is 
 passed in an ichthyic or fish-condition. These are 
 the amphibians, the group to which the frogs and 
 toads, the newts and salamanders belong animals, 
 as we all know, and as we see exemplified in the tad- 
 pole, whose larval forms breathe the oxygen of the 
 water by means of exposed gills, and which in their 
 advanced or adult stage, develop true lungs, and 
 thus approximate the reptilian condition. But we 
 meet as yet with no true reptiles. These appear 
 for the first time in the rocks of the succeeding 
 period, the Permian. 
 
 We have now passed through about two-thirds 
 
12 THE GEOLOGICAL EVIDENCES 
 
 of the known cycle of geological history, or com- 
 pletely through what is known as the Paleozoic 
 period of time. In the Triassic period we have 
 the first evidence of the existence of the highest 
 animals, the mammals, and in the period following 
 this, the Jurassic, of birds, an apparent contradic- 
 tion to the order of appearance. 
 
 Let us here enter somewhat more closely into an 
 examination of the order of appearance that has 
 been outlined, and see what it signifies. I believe 
 we shall find in its analysis both kinds of 
 evolutionary proof that we are in search of. But 
 in order to do this we must satisfy ourselves as 
 to the relationships to one another of the differ- 
 ent animal groups whose histories we have 
 followed. What is a fish, what is an amphibian, 
 and what is a reptile, and what relationship 
 do these three groups bear to one another ? 
 I can in this place only briefly indicate the 
 essential anatomical features of these groups. 
 Beyond having the characters belonging to the 
 Vertebrata in general, fishes may be described as 
 
OF EVOLUTION. 13 
 
 cold-blooded, water-inhabiting animals, breathing 
 by means of ills, having but two chambers to the 
 heart, and rejoicing in a purely systemic circula- 
 tion i. e., the arterialized or oxygenated blood 
 instead of being returned to the heart before being 
 finally distributed, is carried directly from the gills 
 to the different parts of the body. The body, 
 moreover, is provided with fins, which fins are sup- 
 ported by fin-rays. When we compare this general 
 structure with that of an amphibian, such as a sal- 
 amander or frog, we naturally find much difference. 
 The frog breathes by means of lungs, is largely an 
 inhabitant of the land, has three chambers to its 
 heart, has a true pulmonary circulation the blood 
 being first returned from the lungs to the heart 
 before it is finally distributed and the body is des- 
 titute of fins and supporting fin-rays, Thus, there 
 would appear to be but little connection between 
 these two classes of animals. When, however, we 
 inquire into the early history of the frog we find a 
 very close connection, and one that proves the 
 young frog to be more of a fish than anything else. 
 
i 4 THE GEOLOGICAL EVIDENCES 
 
 The familiar tadpole or fish-like form is an inhabit- 
 ant of water, and like the fish it breathes water by 
 means of gills; it has but two partitions to its heart, 
 a non-pulmonary circulation precisely like that 
 of the fish, and the body provided with fins, which 
 are, however, destitute of fin-rays. 
 
 Leaving out certain differences in the osteolog- 
 ical structure of the cranium, we might indeed say 
 that almost the only striking character separating 
 this larval amphibian from the fishes is the absence 
 of fin-rays ; but in whatever way we look upon it, 
 the creature is much more a fish than anything 
 else, and differs less from certain fishes than these 
 do from each other. So that to all intents and pur- 
 poses the frog is a dual creature a fish in its young 
 stage and something else afterwards. Why then, 
 it might be asked, separate the amphibians from 
 the fishes at all? The master mind of Professor 
 Huxley has solved this question. The fishes and 
 amphibians are but sub-groups of a single division, 
 known to naturalists as the Ichthyopsida. I 
 have thus far indicated to you only a one-sided 
 
OF EVOLUTION. 
 
 relationship. The amphibians not only approach 
 the fishes, but the fishes approach equally the 
 amphibians. There exist a limited number of 
 
 1. Ceratodus Forsteri, mud-fish of Australia. 2. Dental armature 
 of same. 
 
 fishes, known as " mud-fishes," inhabitants of the 
 waters of South America, Africa, and Australia, 
 which depart from other fishes so widely as to be 
 
1 6 THE GEOLOGICAL EVIDENCES 
 
 properly constituted -into a distinct class of their 
 own. They are provided, in addition to gills, with 
 true lungs, by means of which they respire the 
 oxygen of the air directly, and with which there 
 stands in immediate relation a pulmonary circula- 
 tion, operated by a heart with three chambers. 
 
 Having thus established the relationship existing 
 between fishes and amphibians, it will be well to 
 consider in how far this relationship also extends 
 to the third group of cold-blooded animals, the 
 reptiles. Manifestly, a reptile is most closely related 
 to the amphibians, from which it differs primarily 
 in never breathing by means of gills, and in having 
 but a single articulation to the base of the skull, 
 instead of the two seen in an amphibian. It may 
 also be added that the amphibian has a naked 
 skin, whereas nearly all reptiles are provided with 
 scales or plates developed in the integument. In 
 other important points of structure such as the 
 lungs, heart, and circulation a reptile agrees essen- 
 tially with an adult amphibian, and indeed more so 
 than certain reptiles agree with one another. The 
 
OF EVOLUTION. 17 
 
 amphibian is, in truth, an animal that binds the 
 three groups together. 
 
 If we now ask ourselves what are the relative 
 positions of these three groups, the answer is a 
 very simple one. The amphibians are obviously 
 higher than the fishes, since they pass from, or 
 through, a fish stage to maturity ; developing in 
 the direction of the reptile, they naturally point 
 to the latter as the superiors in the scale 
 of organization. Recognizing this position, what 
 is the nature of the geological history that they 
 would be likely to tell? That the fishes appeared 
 first, that the amphibians came next, and that 
 these were followed by the reptiles, just as we 
 have seen it actually to have been the case. It 
 is a remarkable fact, and one most confirmatory of 
 the doctrine of evolution, that the history of the 
 individual development of an animal frequently 
 repeats the development of the broad group which it 
 represents. But geological evidence is not entirely 
 satisfied with the evidence of succession, corres- 
 ponding to the law of development, which I have 
 
 (2) 
 
18 
 
 THE GEOLOGICAL EVIDENCES 
 
 1. Dipterus Valenciennesi, Devonian fish. 2. Dental armature of same. 
 3. Tooth of Ceratodus (Trias). 
 
OF EVOLUTION. 19 
 
 just given you; it must sooner or later show that 
 in the period intervening between the first appear- 
 ance of fishes and the earliest development of 
 amphibians there existed a type of fish more 
 closely related to the amphibian than the ordinary 
 fishes in other words, a connecting link more or 
 less closely related to the mud-fishes. Such a form 
 we find in Dipterus and its allies, fishes that belong 
 to the Devonian period of time ; and if any proof 
 were further wanted indicating the antiquity of 
 the existing group of lung-fishes, we have but to 
 point to the occurrence of one of our modern 
 genera, Ceratodus, already in the deposits of the 
 Permian period. Ceratodus, in fact, represents the 
 oldest living vertebrate type known to naturalists. 
 
 There is a remarkable structural peculiarity 
 belonging to a very large number, if, indeed, not to 
 the vast majority, of the earliest amphibians, which 
 seems to distinguish them from all the modern 
 members of the same group of animals. This is a 
 singular labyrinthine infolding of the substance of 
 the teeth, which has given to the group the name 
 
20 
 
 THE GEOLOGICAL EVIDENCES 
 
 of the Labyrinthodontia. Now it is a surprising cir- 
 cumstance that many of the most ancient fishes, or 
 those which preceded the labyrinthodonts in time, 
 
 Labyrinthodon Rutimeyeri, an early amphibian. 
 
 have this same peculiarity of structure, and at the 
 present day we have still a form, the alligator-gar 
 one of the last remaining survivors of that ancient 
 
OF EVOLUTION. 21 
 
 ichthyic group, the ganoids which retains this 
 peculiarity of dental structure. From what has 
 already been said, I believe it will be admitted that 
 we have the strongest kind of evidence to show 
 that the amphibians have been developed from the 
 fishes, and further, that one of the most striking 
 
 Section of labyrinthodont tooth. 
 
 characters of these most ancient amphibians is 
 a character which had already been developed in 
 that class of animals whose position is unmistak- 
 ably below them in the scale of organization. 
 
 Passing now to a consideration of what some 
 choose to call the rather anomalous appearance of 
 
22 THE GEOLOGICAL EVIDENCES 
 
 
 
 birds and mammals in Mesozoic time /. e., the 
 appearance first in time of the more highly organ- 
 ized group I am compelled to ask, in what respect 
 is this appearance anomalous ? What special rela- 
 tion do these two groups hold to one another and 
 to the animals that succeed them; and in accord- 
 ance with what law should it be required that the 
 order of appearance be reversed? Manifestly, only 
 if it can be shown that the line of descent of the 
 mammal passed through that of the bird; otherwise 
 the two need bear no special relation to one another. 
 What is the zoological position of the bird, and what 
 that of the mammal ? At first sight a bird appears 
 to be most sharply defined, and absolutely isolated, 
 from all other members of the great group of 
 animals. And our conception of this isolation 
 would probably have remained intact to the present 
 day were it not for the very remarkable discoveries 
 which the paleontologist has brought to light dur- 
 ing the last half-century. 
 
 Briefly defined, a bird is a hot-blooded verte- 
 brate animal, provided with feathers to its body, 
 
OF EVOLUTION. 23 
 
 with a complete pulmonary circulation operated by 
 a four-chambered heart, and with the anterior 
 appendages so modified as to permit of navigation 
 through the air ; the mouth is destitute of teeth, 
 a character which serves to separate it from 
 the greater number of other vertebrate animals. 
 This is our conception of a modern bird. But 
 what has been its earlier history ? I have 
 placed before you the figure of a remarkable 
 creature, known as the Archaeopteryx, only two 
 individuals of which have thus far been discov- 
 ered. The first, now deposited in the British 
 Museum, was found about twenty-five years 
 ago, and the second some ten years since, and 
 constitutes to-day one of the treasures of the 
 museum of Berlin. They were both found in 
 the lithographic-stone quarries of Solenhofen, 
 Bavaria, and in deposits that by geologists are re- 
 ferred to the Jurassic period of time. This remark- 
 able creature, which was of about the size of a 
 raven, had a generally bird-like head, but differing 
 from all modern birds, the head was supplied with 
 
24 THE GEOLOGICAL EVIDENCES 
 
 true teeth in the extremities of both the upper and 
 lower jaws, which teeth were implanted in distinct 
 sockets, as in the more highly constituted reptiles. 
 The body was provided with well-developed feath- 
 ered wings, but again, departing from true birds, 
 the rest of the body, except the tail and parts 
 of the legs, appears to have been either largely 
 
 Head of the Berlin Archseopteryx. 
 
 naked, or but scantily clothed with feathers ; the 
 legs and feet were bird-like in structure, but in 
 the hand and tail we have a remarkable combi- 
 nation of reptilian and avian characters. The 
 latter, instead of being made up in principal 
 part of feathers radiating from a greatly con- 
 densed vertebral axis, is prolonged into a long 
 
ARCH.EOPTERYX. 
 
 Specimen in the Berlin Museum. 
 
OF EVOLUTION. 25 
 
 succession of vertebrae, from two sides of which 
 feathers are given off in pairs. 
 
 Is this creature a bird or reptile ? I am free to 
 admit that I am unable to answer this question to 
 my absolute satisfaction, although I would prob- 
 ably say that it is more nearly bird than reptile. 
 But if bird it is manifest that we must very consid- 
 erably modify our conception of what a bird really 
 is. We must modify our notions as to the value of 
 the character afforded by the absence or presence of 
 feathers, and deduct from our definition that part 
 which pertains to the presence of teeth. But that 
 the matter of teeth is of no very great moment is 
 proved by the existence of these structures in a 
 group of remarkable and indisputable birds, which 
 have been discovered during the last few years 
 in our own western territory. These ar, i. 1 ie 
 Odontornithes, of which two members, Ichthy- 
 ornis and Hesperornis, are represented on the 
 diagrams before you. 
 
 That these earliest birds were largely reptilian 
 in character can, with the evidence before us, 
 
26 THE GEOLOGICAL EVIDENCES 
 
 Hesperornis repays. Specimen in the Peabody Museum, New Haven. 
 
OF EVOLUTION. 27 
 
 scarcely be gainsaid ; and if it can be shown with 
 equal force that many of the earlier reptiles pos- 
 sessed characters belonging to birds, have we not 
 the right to assume that the two classes of 
 animals are very closely related, and that they be- 
 long to one and the same stock ? And since the 
 modern birds have practically dropped all their 
 reptilian characters, have we not the right to 
 assume further that birds are descended from rep- 
 tiles, of which they represent only a diverging 
 group ? Is it not merely a repetition of the tale 
 that is furnished by the development of the am- 
 phibian from the fish so beautifully shown, apart 
 from geological history, by the tadpole before 
 our eyes and the reptile from the amphibian ? 
 It is true that we know of no modern bird 
 which passes through an absolute reptilian stage, 
 but does not embryology tell us that one of 
 the primary structures separating birds from rep- 
 tiles, the feather, is merely a modified scale, and 
 that it originates as a true scale ? 
 
 If the combination of the modern and ancient 
 
28 
 
 THE GEOLOGICAL EVIDENCES 
 
 characters of birds approximates them so closely 
 to reptiles, what indeed, it might be asked, are the 
 
 Ichthyornis victor. Specimen in the Peabody Museum, New Haven. 
 
 fundamental characters which separate them from 
 reptiles ? We have still the four-chambered 
 
OF EVOLUTION. 29 
 
 heart, the presence of wings, and certain struc- 
 tures connected with the hinder extremities. But 
 the first distinction is immediately disposed of by 
 the case of the crocodiles and alligators, which, 
 alone among reptiles, have the four recognized 
 chambers of the heart belonging to the highest 
 animals. The matter* of wings is also disposed of 
 by those remarkable reptilian creatures belonging 
 to the same epoch of geological time as the 
 earliest bird, the pterodactyls, which in many 
 other characters such as the light structure and 
 manner of support of the head, the presence of a 
 well-developed keel or carina to the breast-bone, 
 etc. also approximate the birds. Furthermore, 
 we are well aware that in the large group of stru- 
 thious birds the ostriches, cassowaries, and apter- 
 yxes the wings are so little developed as to be 
 all but functionless. We are hence driven to the 
 remaining characters derived from the structure 
 of the hind-quarters and their appendages. 
 
 The most careless observer is aware that a bird 
 can at almost all times be distinguished from a 
 
30 THE GEOLOGICAL EVIDENCES 
 
 I. 2. 
 
 Pterodactyls. 1. Rhamphorhynchus (restored) ; 2. Pterodactylas. 
 
OF EVOLUTION. 31 
 
 reptile by its mode of progression its elevation 
 on the hinder extremities alone. But this mode 
 of progression does not differ" more from that of a 
 reptile than does the method of a snake from that 
 of a turtle, yet both are reptiles. It is in the relative 
 disposition of the parts that we find the important 
 difference. In all birds the pelvic girdle, which 
 consists of the three bones recognized in man as 
 the pubis, ischium, and ilium, has the pubis 
 directed in a direction more or less parallel with 
 that of the ischium ; in other words, backward. 
 In all reptiles, on the other hand, this bone is 
 directed forward. Again, in all, or nearly all 
 birds, there is a prominence, known as the cnemial 
 crest, developed on the upper part of the tibia, 
 for the attachment of the powerful muscles of the 
 leg. This is wanting in reptiles ; and further, 
 there are certain peculiarities connected with the 
 articulation of the foot to the leg in birds which 
 almost immediately serve to distinguish these 
 parts from the similar parts of reptiles. Have 
 we any reptilian forms which at all meet the 
 
32 THE GEOLOGICAL EVIDENCES 
 
 divergencies in character here brought out? 
 
 All of you who have visited our museum will 
 
 remember the large -animal, mounted on the east 
 
 1, Leg of a hen ; 2, of a hen-embryo ; 3, of a dinosaur (Camptonotus], 
 showing disposition of pelvic bones. 
 
 side, which was discovered on the Hopkins Farm, 
 near Haddonfield, N. J., some thirty years ago. 
 
OF EVOLUTION. 33 
 
 The Hadrosaurus, as it is called, is the represent- 
 ative of a large group of reptiles, the dino- 
 saurs, or terrible reptiles, many of whose mem- 
 bers depart just in that much from other reptiles 
 as is indicated by the above characters supposed 
 to belong to birds. In other words, we have 
 here both small and giant animals, whose pro- 
 gression was either largely, or mainly, effected by 
 the hinder appendages alone ; in which the pubic 
 bone of the pelvis was directed backward, more 
 or less in a direction parallel with that of the 
 ischium ; in which the tibia was provided with a 
 well-developed cnemial crest ; and in which, finally, 
 the ankle-joint of the foot and the disposition of 
 the toes were in accordance with the disposition 
 seen in birds. Many of these animals, further- 
 more, had the pneumatic character of the bones 
 of birds, ensuring a certain amount of lightness 
 to an otherwise ponderous frame. These singular 
 creatures, one of which, the Iguanodon, is repre- 
 sented in the diagram before you, first appeared 
 
 in the Triassic age, or in the period immediately 
 
 (3) 
 
34 THE GEOLOGICAL EVIDENCES 
 
 Iguanodon Bernissartcnsis. Specimen in the Brussels Museum. 
 
OF EVOLUTION. 35 
 
 preceding the advent of the earliest known bird, 
 Archaeopteryx, although they do not acquire 
 any special development until the period following, 
 the Jurassic. It is to them that we owe those 
 remarkable foot-tracks which have made the red- 
 sandstone of the Connecticut Valley famous, 
 and which for full half a century after their 
 discovery were unhesitatingly referred to giant 
 birds of a type thought to be more or less 
 identical with that of the ostrich. So singularly 
 striking are the bird characters of these reptiles, 
 that for many years they have been looked upon 
 by many naturalists as the stock .whence the non- 
 flying or ostrich-like birds have been derived 
 the pterodactyls, or winged reptiles, furnishing 
 the line to the winged or flying birds and, indeed, 
 it has been thought that very nearly the exact type 
 could be pointed out which gave departure to 
 the birds. This has been indicated by Professor 
 Huxley to be near to Compsognathus. However 
 correct or incorrect this determination may be, 
 there can be no doubt in the face of the evidence 
 
36 THE GEOLOGICAL EVIDENCES 
 
 before us, as coming from the side of both rap- 
 tile and bird, that the two classes of animals 
 are simply modifications of the same stock, 
 
 Compsognathus longipes. 
 
 and that the one (the bird) is a derivative of 
 the other (reptile). The zoological relationship 
 clearly points to the nature of this derivation, 
 
OF EVOLUTION. 37 
 
 which the geological evidence amply and fully 
 confirms. 
 
 Were the Mammalia in any way specially 
 connected in their zoological relationship with 
 birds, we should naturally expect to find them 
 appear in succession to the birds. The vertebrate 
 line would then be an absolutely successive one. 
 But this relationship does not exist. For a 
 long time zoologists have held to the opinion 
 that these highest animals were more nearly 
 related to the reptiles than to any other class 
 of the Vertebrata, but the evidence supporting 
 this conclusion was all but the very weakest. 
 The fundamental conception of a mammalian de- 
 parts so widely from that of any other repre- 
 sentative of the great series to which it belongs, 
 that an actual comparison between it and the 
 nearest forms appears almost impossible. But 
 recent researches have thrown new light upon 
 the problem. That most obvious distinction 
 separating the Mammalia from all other animals 
 namely, that they bring forth their young 
 
THE GEOLOGICAL EVIDENCES. 
 
 alive, and that the young is nourished directly 
 from the parent has generally been considered an 
 impassable obstacle in the way of correlating these 
 animals with animals lower in the scale of organ- 
 ization than themselves. It is barely three years 
 since we had the startling announcement, made 
 
 Australian duck-bill (Ornithorhynchus). 
 
 independently by two investigators, and through 
 observation on two distinct animals, that at least 
 two of the mammalian types, the duck-bill and 
 the echidna, instead of developing their young in 
 the normal manner of the animals of their class, 
 
OF EVOLUTION. 39 
 
 bring them forth within the egg, and that the early 
 development of the egg corresponds with the 
 development of the egg of the reptile. This is 
 one of the most extraordinary discoveries made 
 in zoology during the last decade, and so 
 remarkable is it, that when a similar announce- 
 ment was made some sixty years ago, and by 
 
 Spiny hedgehog (Echidna). 
 
 one of the most eminent of naturalists living at 
 the time, it met with absolute unbelief. 
 
 The evidence bearing upon the inter-relationship 
 of mammals and reptiles is rapidly accumulating, 
 and it will probably not be long ere we will 
 be able to point to the connecting form between 
 
40 THE GEOLOGICAL EVIDENCES 
 
 the two. From the existing evidence before us 
 we are safe in concluding that the line of descent 
 of these animals is direct from a reptilian stock ; 
 and this being admitted, there is no anomaly in 
 the fact that the mammals appeared before the 
 birds. Both birds and mammals are divergent 
 modifications from a common axial stock. It 
 is certainly an interesting feature bearing upon 
 the reptilian relationship of the Mammalia that 
 the earliest reptilian forms, those of the Permian 
 period, are the only animals which possess the 
 remarkable dental characters of the Mammalia. 
 These, as is well known, have the teeth di- 
 vided into three series incisors, canines, and 
 molars a structure unknown among other living 
 animals. But in the reptiles of the Permian 
 period, which may perhaps be looked upon as 
 the ancestral stock whence the Mammalia were 
 derived, the same dental feature is presented. 
 

 OF EVOLUTION. 41 
 
 II. 
 
 We have thus followed the succession of the 
 higher groups of animals through geological time, 
 and find that this succession is one that is in 
 perfect harmony with structural relationship. Had 
 we no other evidence to offer in favor of evo- 
 lution than that which I have laid before you as 
 coming from fishes, amphibians, reptiles, and birds, 
 this evidence, in my mind, would of itself be amply 
 sufficient to prove the position. But there is no 
 lack of other evidence, and evidence fully as 
 strong, and, if possible, still stronger than that 
 which I have given you. Thus, if we trace the 
 
42 THE GEOLOGICAL EVIDENCES 
 
 histories of the primary and secondary groups 
 of the larger divisions of the animal kingdom, 
 we meet with a repetition of much the same 
 order of appearance. The fishes, for example, are 
 represented in the oldest formations exclusively 
 by such forms as betray a comparatively low 
 grade of organization ; these are the sharks and 
 ganoids, in which the vertebral column remains 
 largely in the embryonic condition, becoming only 
 partially ossified in most cases. The lung-fishes, 
 which are a direct modification of the ganoid 
 type, representing, however, a considerable amount 
 of specialization in the development of a respir- 
 atory apparatus adapted to breathing directly the 
 oxygen of the atmosphere, appear considerably 
 later, possibly in the Carboniferous period, but are 
 already preceded by an intermediate type, that 
 of the dipteroid ganoid. The more highly organ- 
 ized fishes, the teleosts, or bony fishes, appear for 
 the first time, as far as we know, in the deposits 
 of the Cretaceous period, and may consequently 
 be looked upon as a comparatively modern group ; 
 
OF EVOLUTION. 43 
 
 but even here we find that this highest group was 
 immediately preceded in time by a type of ganoid- 
 plated fishes, the Leptolepidae, which in so far 
 partake of the characters of both ganoid and 
 teleost as to have induced naturalists to place 
 them alternately now in the one group, now in 
 the other. 
 
 When we cast a broad glance over the existing 
 fish fauna of the globe, and compare it with that 
 of the earlier geological periods, we find that it 
 differs, not only in the introduction of types of a 
 higher grade of organization, but in the actual elim- 
 ination of the lower structural forms. The 
 ganoids, for example, which are numbered by hun- 
 dreds of species in the interval between the De- 
 vonian and Jurassic periods, are practically extinct 
 at the present day, numbering but a mere hand- 
 ful of species. A somewhat similar, although less 
 marked, elimination is also distinctive of the 
 selachians (sharks, rays). We thus find a com- 
 plete rotation marking the succession of these 
 animals. Evolution or transformism is the 
 
44 THE GEOLOGICAL EVIDENCES 
 
 expression of necessity for a change ; hence, the 
 rotation of forms. Among the amphibians, rep- 
 tiles, and birds, likewise, we observe that the older 
 forms are very different from those now living, 
 but the difference becomes less and less marked 
 as we approach the present day. The same 
 holds equally true with the mammals, whose ear- 
 liest representatives are again forms of a very low 
 grade of organization. These are the marsupials 
 of the Triassic and Jurassic periods, forms more 
 or less closely allied to some of the lowly types 
 inhabiting the Australian continent. 
 
 The chart before you indicates the rise and fall of 
 this highest order of animals. It will be seen that 
 they date their first appearance from the Triassic 
 period, where, however, there are but three or four 
 genera, and a barely larger number of individuals, 
 represented. One of these, and the first species 
 described, is on the table before you, known as 
 Dromatherium. A further development takes place 
 in the Jurassic period, when a broad hiatus fol- 
 lows. No mammalian remains have thus far 
 
OF EVOLUTION. 45 
 
 been discovered in any indisputable Cretaceous 
 deposit, and I may at once confess my inability 
 to satisfactorily account for this non-appearance. 
 But I feel perfectly safe in prophesying that they 
 will yet be found, and were I as sure of many 
 other things generally considered positive as I am 
 of this one, I could remain satisfied. 
 
 In the first stage of the Tertiary period, known 
 as the Eocene, we meet with the earliest of the 
 placental mammals, or those forms in which direct 
 union is established between the young and parent 
 during the process of development. From this 
 period, it might be said, dates the origin of our 
 modern fauna. It will be seen from the chart 
 before you that only about one-half of the exist- 
 ing orders of quadrupeds are represented in the 
 Eocene period ; these are the marsupials, insect- 
 ivores, rodents, whales, hoofed-animals, bats, 
 lemurs, and possibly even monkeys. In addition 
 to these there are a number of orders which 
 have no living representatives at the present 
 day. In the Miocene, or middle Tertiary period, 
 
46 THE GEOLOGICAL EVIDENCES 
 
 there are superadded the edentates, or tooth- 
 less animals, the carnivores, sirenians, elephants, 
 and true monkeys. Per contra, the special Eocene 
 orders to which reference has just been made, have 
 completely disappeared, so that in the Miocene 
 period only those orders of quadrupeds are 
 represented which have living representatives in 
 our existing fauna. But it must not be construed 
 from this that there is a true faunal identity ; this 
 only appears in the most recent or Post-Pliocene 
 period. 
 
 From the beginning of the Tertiary period 
 to the present day there is a steadily pro- 
 gressive approximation to modern type-structures, 
 but this approximation is a very gradual one. 
 This will appear clear to you when it is stated 
 that, with barely a single exception, not only are all 
 the Eocene species and genera of mammals differ- 
 ent from those of the present day, but even the 
 families are very largely different ; furthermore, 
 there are a number of orders indicated which have 
 no representation in the modern fauna. The only 
 
OF EVOLUTION. 47 
 
 known living types of mammals which are generi- 
 cally represented in the Eocene period are two gen- 
 era of bats Vespertilio and Vesperugo and the 
 opossum (Didelphys). In the Miocene period the 
 faunal difference is measurably lessened by the 
 elimination of the special orders which belong to 
 the period preceding, and by the introduction of a 
 considerable number of modern genera, such as 
 the porcupine, beaver, squirrel, rabbit, tapir, rhi- 
 noceros, hippopotamus, hog, deer, giraffe, elephant, 
 cat, dog, and hyena. The families, moreover, are 
 very largely identical with existing ones, so that 
 in its entirety the Miocene fauna may in a broad 
 way be looked upon as distinctly modern. 
 The species of this period are, however, all, or 
 nearly all, distinct .from those now living. In the 
 period following, the Pliocene, there is a still 
 further approximation to the modern fauna in 
 the introduction of an additional number of exist- 
 ing types such as the sheep, goats, and oxen, 
 the bear and camel, and among monkeys, the 
 macaques. Indeed, the greater number of the 
 
48 THE GEOLOGICAL EVIDENCES 
 
 genera are identical with the genera of to-day, and 
 even a limited number of living species appear 
 for the first time. One of these is the common 
 hippopotamus, which, consequently, represents 
 about the oldest type of existing quadrupeds. In the 
 Post-Pliocene period the correspondence between 
 the existing and extinct faunas is still further in- 
 creased through the large preponderance of recent 
 species. On the border-line of this and the pre- 
 ceding period we meet with the earliest unequiv- 
 ocal remains of man himself. 
 
 The correspondence between the recent and 
 extinct mammalian faunas may be conveniently 
 summarized as follows : 
 
 Post- Pliocene period. 
 Mammalia principally of living species. 
 
 Pliocene period. 
 Mammalia principally of recent genera living 
 
 species rare. 
 
 Miocene period. 
 Mammalia principally of living families extinct 
 
 genera numerous; species extinct. 
 
OF EVOLUTION. 49 
 
 Eocene period. 
 
 Mammalia with numerous extinct families and 
 orders. With two or three exceptions, all 
 the genera extinct. Species all extinct. 
 I appeal to the facts before you, and ask, Could 
 there be a more beautiful demonstration of the rise 
 and fall of a fauna tending in the direction of gen- 
 eral succession ? Do we not see in the wreck of 
 the past faunas the roots of the fauna of our own 
 day, and can we close our eyes to the evidence 
 of development that is here presented to us ? A 
 skeptical mind may, however, still urge that this 
 is but a fortuitous succession, and that we have 
 failed to bring forward proof of such transformism 
 as will permit us to see that the modern groups 
 which succeed the more ancient ones are necessa- 
 rily developed from these. But proof in this 
 direction is by no means wanting. When we 
 trace back the histories of some of our existing 
 groups of animals we find that the characters by 
 which they are defined become less and less 
 
 marked, until they are almost completely lost, 
 
 (4) 
 
50 THE GEOLOGICAL EVIDENCES 
 
 when the group as such disappears. In other 
 words, the specialized animals of to-day, or rather 
 their representatives, become more and more 
 generalized as we trace them back in geological 
 time. Thus, the Carnivora lose much of the true 
 type of carnivore structure in the early part of the 
 Miocene period, and by almost insensible modifi- 
 cations pass off into a group of animals, their im- 
 mediate forerunners in the Eocene period the 
 Creodonta which combine about equally the 
 characters of the Carnivora with those of the Insect- 
 ivora. Thus, the Creodonta stand intermediate 
 between two of our modern groups which are 
 seemingly very far removed from one another. In 
 the same way, if we take some, of the more prom- 
 inent families of the Carnivora, the bears and 
 dogs, for example, we find that their special 
 structural features likewise disappear the bears 
 becoming less and less bears, and the dogs less and 
 less distinctively dogs, until we meet with an 
 animal, the Amphicyon, which is about as much the 
 one as the other. Similarlv, the cats become less 
 
OF EVOLUTION. 5 i 
 
 
 
 and less cat-like, and they can be traced down to 
 animals which on the one side link them to the 
 civets, and on the other, to the dogs. 
 
 Again, the large group of the lemurs, those 
 singular representatives of the Quadrumana which 
 
 impress such a distinct individuality upon the 
 
 
 fauna of Madagascar, become less and less lemur- 
 
 ine the farther back we trace them, approximating 
 very closely to the type of insectivore structure. 
 So complete is this approximation that the most 
 experienced zoologists are at a loss to determine 
 in many cases whether certain ancient types are 
 in reality lemurs or insectivores. Other animal 
 groups likewise converge toward this same group 
 of the Insectivora, which (or certain immediate 
 allies) are now considered to represent the stem 
 from which most of the existing placental mam- 
 mals have been developed. We thus see how 
 unstable are the characters which have been 
 formulated toward the proper delimitation of ani- 
 mal groups. The beautiful classification of Cuvier, 
 which was founded on the assumption that the 
 
THE GEOLOGICAL EVIDENCES 
 
 living organisms represented are the only types 
 known to nature, is no longer applicable in the 
 sense it was intended by its illustrious promulgator, 
 and it is vain to plead the individuality or want 
 of convergence of animal groups. 
 
 But let us press the inquiry still further, and 
 
 Different types of tail - structure. 1. Homocercal (modern form). 
 2. Heterocercal (ancient form). 3. Diphycercal (primitive form). 
 
 within a narrower sphere. I have thus far treated 
 of the relations of the different higher groups 
 of animals, the limitations of which may not be 
 very clear to the non-scientific mind. But where, 
 the skeptical mind may ask, are the proofs of 
 
 
OF EVOLUTION. 53 
 
 individual variation, of variation in special organic 
 structures ? I will attempt to lay before you 
 some of these, and take my first illustration from 
 the class of fishes. In the vast majority of the 
 ordinary bony fishes, as is well known, the tail is 
 nearly equally divided into two lobes, and is said 
 
 Semionotus leptocephalus.G&noid fish from the Lias of Germany. 
 
 to be homocercal. In sharks and rays, as rep- 
 resentatives of the cartilaginous fishes, on the 
 other hand, the tail is typically unequally lobed, 
 and is said to be heterocercal. This, as might 
 have been expected, seeing that the sharks 
 
54 THE GEOLOGICAL EVIDENCES 
 
 represent a comparatively low ichthyic type, is also 
 the case with the earliest fishes, with both sharks 
 and ganoids, and not till an intermediate 
 middle period do we find a tendency on the 
 part of the tail toward homocercality. A 
 large proportion of the Jurassic ganoids are 
 provided with the modern form of tail, and these, 
 again, are preceded by a form, Semionotus, in 
 which the tail is of a distinctively transitional 
 character. 
 
 As pertaining to the group of reptiles I can 
 present to you an equally beautiful and con- 
 clusive case of the modification of special struct- 
 ures. The crocodiles represent a fairly ancient 
 group of reptiles, beginning with the Triassic 
 period of time ; the recent genera date from the 
 period of the chalk. In their history they pre- 
 sent a remarkable series of developmental changes. 
 In the modern crocodiles, and in those of the 
 later Cretaceous period, two series of bones be- 
 longing to the roof of the mouth, known as the 
 palatines and pterygoids, are so disposed as to 
 
OF EVOLUTION. 55 
 
 form the boundaries of the posterior nostrils ; 
 in the crocodiles that preceded these, or those 
 of the early Cretaceous and Jurassic periods, only 
 the palatines are produced to form these nares; 
 and in the still earlier and earliest forms, those 
 of the Triassic period, neither the one bone nor 
 the other is concerned in the structure of the 
 parts in question. Correlatively with these changes 
 other modifications, scarcely less significant, mark 
 the rise of this very remarkable animal group. 
 Thus, the earlier crocodilian forms retain a 
 primitive character in the biconcave form of the 
 vertebrae a structure belonging primarily to the 
 lowest group of vertebrates, the fishes. This 
 structure is replaced in the Cretaceous period 
 by the cup-and-ball, or proccelous vertebra, which 
 is also the type of the Tertiary and modern 
 forms. 
 
 Other instances of similar variation and pro- 
 gression could readily be cited, but my limited 
 time will only permit me to dwell upon a few 
 very striking cases drawn from the class of 
 
56 THE GEOLOGICAL EVIDENCES 
 
 mammals. The history of the horse furnishes, 
 perhaps, the most complete series of structural 
 modifications which permit us to trace the ances- 
 try of an animal in very nearly its minutest 
 details. The chart before you indicates these mod- 
 ifications in a series of horse-like animals which 
 carries the line of descent of our modern animal 
 back to the Eocene period, and to an animal 
 so very different, that were it known by itself 
 alone, it would be classified by zoologists, not only 
 as a species distinct from the modern horse, but 
 as a distinct genus, representing an entirely differ- 
 ent family, and even a wholly different sub-order. 
 The connecting ties, however, absolutely estab- 
 lish the serial line of progression, and indelibly 
 mark the pedigree. The history of the Euro- 
 pean horse is almost as complete as that of the 
 American, but remarkable though it may appear 
 on any but an evolutionary hypothesis, its first 
 ancestral forms include an animal different from 
 any of the earlier equine progenitors of the 
 New World, and one that holds equal claim to 
 
OF EVOLUTION. 57 
 
 being the true progenitor of the tapir and tapir- 
 oid animals. This is the Palaeotherium, several 
 species of which, ranging in size between the 
 
 Palseotherium. Ancestral form of the European horse (Lower Tertiary 
 of the Paris Basin). 
 
 deer and horse, have been described, and whose 
 remains from the early Tertiary strata of the 
 Paris Basin furnished the material for one of 
 
58 THE GEOLOGICAL EVIDENCES 
 
 the classic memoirs of the illustrious Cuvier. 
 The modifications here referred to are primarily 
 the greater or less differentiation of the elements 
 of the foot and leg (fore and aft). In the modern 
 horse there is but a single toe to each foot, which 
 is supported by a single metapodial (cannon-bone), 
 but in the more ancient horse-like animals the feet 
 were polydactyl in character, being furnished with f 
 three, four, or even five toes. This is seemingly 
 a broad difference, and it might reasonably be 
 supposed that there must exist strong grounds 
 for uniting animals that appear so widely removed 
 from one another. The rationale of our classifica- 
 tion is the fact that between the earliest horse-like 
 animals and the modern horse we have a series 
 of transitional forms which show almost every 
 grade of foot structure leading from polydactyl- 
 ism to monodactylism, the toes undergoing grad- 
 ual reduction in number, and (excepting the single 
 toe that is retained) growing smaller in size 
 as we proceed from the more ancient to the more 
 modern forms. This gradation is beautifully 
 
OF EVOLUTION. 
 
 59 
 
 Horse. 
 
 Pliohippus. 
 
 (Upper Pliocene.) 
 
 Hipparion. 
 (LowerPliocene.) 
 
 Anchitherium . 
 (Miocene.) 
 
 Mesohippus. 
 (Oligocene.) 
 
 Hyracotheriurn. 
 (Eocene.) 
 
 Successive forms of the American horse type. (After Marsh . ) 
 
6o 
 
 THE GEOLOGICAL EVIDENCES 
 
 illustrated in the chart before you, where the 
 supernumerary, and to an extent functionless, 
 toes of the Eocene Hyracotherium, which is fol- 
 lowed by the less and less distinctively polydactyl 
 
 Hipparion gracile. Skeleton in the museum of Munich. 
 
 forms of the Oligocene, Miocene, and early Plio- 
 cene periods, are seen to be represented in the 
 later Pliocene Pliohippus and the recent horse 
 (Equus) by a simple pair of " splints" attached 
 to the cannon-bone. Beyond the Hyracotherium 
 
OF EVOLUTION. 
 
 61 
 
 we have still a full five-toed animal, the Phe- 
 nacodus, which is now generally recognized as the 
 earliest known progenitor of the horse tribe. 
 Correlatively with the progressive changes in 
 the structure of the foot, there are equally well- 
 
 i. 
 
 2. 
 
 4- 
 
 Successive stages in the development of the European h^se. 1. Palae- 
 otherium (Eocene) ; 2. Anchitherium (Miocene) ; 3. Hipparion (Pli- 
 ocene) ; 4. Equus (modern). 
 
 marked modifications in the disposition of the 
 bones of the arm and leg, and in the form and 
 complexity of the grinding teeth, which are also 
 illustrated on the chart before you. 
 
62 
 
 THE GEOLOGICAL EVIDENCES. 
 
 That some of these modifications belong as 
 well to the horse as a specific animal as they do 
 to the horse as a tribe, is conclusively shown 
 
 Recent didactyl horse. (After Marsh.) 
 
 by the circumstance that we even now occa- 
 sionally meet with living horses possessed of 
 more than one toe to the foot, and, indeed, it 
 has been affirmed although the statement still 
 
OF EVOLUTION. 63 
 
 lacks full confirmation that the embryo horse is 
 polydactyl. These are important facts bearing 
 upon the developmental history of the animal. 
 
 The cameline animals, especially those of the 
 New World, present a connecting series or chain 
 almost as complete as that which has been estab- 
 lished for the horse. The existing animals of this 
 group, in common with other ruminants, have 
 the bones of the middle-foot (the metapodials) 
 united into a single " cannon-bone," as in the deer, 
 but they differ strikingly from all other mem- 
 bers of the broad group which they represent 
 in possessing a pair of incisor teeth in the upper 
 jaw. By some naturalists the absence of superior 
 cutting teeth in the ruminants has been supposed 
 to stand in direct connection with the develop- 
 ment of horns, but just in what manner has not 
 been definitely determined. It is, however, an 
 interesting circumstance, that the cameline forms, 
 almost alone among ruminants, are entirely des- 
 titute of horns, while they possess the peculiar 
 dental character above referred to. 
 
64 THE GEOLOGICAL EVIDENCES 
 
 In following back the ancestral line of these 
 hornless ruminants we can detect a series of 
 very remarkable and gradual modifications which 
 connect the modern animal with animal forms 
 very unlike itself. Thus, in one of the earliest 
 members of the cameline series, the Oligocene 
 or Miocene Poebrotherium, whose species appear 
 to have had the slender and graceful proportions 
 of the modern gazelles, the metapodial bones 
 were distinct, and the mouth was furnished with a 
 complete series of incisor teeth. This distinguish- 
 ing dental character is retained in the succeed- 
 ing Protolabis (Middle Miocene), but whether or 
 not the metapodials were united into a single 
 cannon-bone is still unknown. In the Upper Mio- 
 cene Procamelus, whose forms ranged in size 
 intermediate between the sheep and camel, the 
 incisor teeth have been reduced to the normal 
 number found in the camels, although the pre- 
 molars still conform to the formula |, instead of 
 f, which distinguishes the genus Camelus. An 
 intermediate position between Procamelus and 
 
OF EVOLUTION. 65 
 
 Camelus is held by the Pliocene genus Pliau- 
 chenia, which possesses but three premolars in 
 the lower jaw, while nearly the extreme term 
 of reduction in this part of the dental series is 
 found in the late Pliocene and recent llamas 
 (Auchenia), which retain but two premolars in 
 the upper jaw and a single one in the lower 
 jaw. Finally, in the nearly contemporary genus 
 Holomeniscus, which embraced animal forms fully 
 equalling the camel in size, and ranging from 
 Oregon to the valley of Mexico, there is but a 
 single premolar left to each side of either jaw. 
 
 The eliminative development that has here 
 been traced corresponds very closely with the 
 conditions presented by the living animal in 
 passing from its embryonic to its adult condi- 
 tion. Thus, in the foetal condition of probably all 
 ruminants the metapodial bones are distinct, as in 
 the early Poebrotherium ; moreover, the animals 
 are provided with cutting teeth in the upper 
 ja\v, in the manner of their ancient progenitors. 
 
 Professor Cope, who has given close attention to 
 
 (5) 
 
66 THE GEOLOGICAL EVIDENCES 
 
 the study of the development of the cameline 
 race, further shows that very young camels have 
 the additional premolar of Pliauchenia, and that 
 this tooth is shed at an early period, very rarely 
 persisting for any length of time. Similarly, the 
 anterior premolar of the normal camel is found 
 in the young llama, but it is dropped long before 
 the animal attains maturity. 
 
 The investigation of the causes which have 
 wrought these remarkable changes in the animal 
 frame constitutes more properly a part of zoolog- 
 ical or physiological inquiry, and I can but briefly 
 refer to the modifications as resulting primarily 
 from the interaction of mechanical forces. The use 
 and disuse of parts must necessarily have a direct 
 bearing upon their ultimate development, and sim- 
 ilarly the manner of use must largely influence the 
 manner of growth of such parts. These are con- 
 ditions known to us in our every day experience 
 but, owing to the very limited time over which our 
 direct observation extends, we are generally able 
 to detect only minor changes, and miss the grander 
 
OF EVOLUTION. 67 
 
 effects which are dependent upon the action of 
 time. The swift-footed animal, which in the pro- 
 cess of rapid locomotion elevates the body so as 
 to weight it principally upon the extremities of the 
 toes, leads the way to the gradual disuse of those 
 toes which, in the required position, are no longer 
 able to give support to the body ; hence, a conse- 
 quent degeneration, and the formation of those 
 apparently " accessory " and more or less func- 
 tionless toes which we see in the hog and many 
 other animals. Similarly, the necessity for a rigid 
 frame combined with lightness would tend to 
 bring about a consolidation of those bones, like 
 the metapodials, whose independent action may 
 now no longer be required. The character of the 
 food supply, necessitating definite methods in the 
 way of eating or mastication, must have a direct 
 effect upon the masticating apparatus, and con- 
 duce toward the formation of the special dental 
 structures which are distinctive of the different 
 animal groups. 
 
 Perhaps no more beautiful illustration of the 
 
68 
 
 THE GEOLOGICAL EVIDENCES 
 
 special modification of a certain organ or structure 
 can be found than that exemplified in the develop- 
 ment of the deer's horn. Everyone is aware that 
 in our ordinary deer with branched antlers the 
 process of growth is a regular and successive 
 one. Before the first shedding we have a single 
 
 Successive stages in the development of the stag's antler. 
 (After Gaudry.) 
 
 solid horn ; after this shedding a single tine is 
 developed ; then a second, and a third, until we 
 have the complicated structure of the typical ant- 
 ler. Now, precisely this system of progression 
 can be traced in the geological history of these 
 
OF EVOLUTION. 
 
 69 
 
 animals. In the early cervine animals of the 
 Middle Miocene period, as has been so clearly 
 stated by Prof. Boyd Dawkins, the horn is a simple 
 
 2. 
 
 4- 
 
 Stages in the geological development of the deer's antler. 
 1 (Dicrocerus) , Miocene ; 2, Upper Miocene ; 3, Pliocene ; 
 4, 5 (5, Cervus Sedgwickii], Newer Pliocene. 
 
 forked crown; in the Upper Miocene it becomes 
 more complex, but is still small and erect, as in 
 the roe ; in the Pliocene it becomes larger and 
 
70 THE GEOLOGICAL EVIDENCES 
 
 longer, and altogether more complex and differen- 
 tiated, some' forms, such as the Cervus dicranios of 
 Nesti, having the most complicated antlers known 
 either in the living or fossil state. Seeing this 
 steady progression in the complication of the ant- 
 ler, it might naturally be expected that were we to 
 trace this development backward we should grad- 
 ually come upon a zero of complication, and that 
 eventually the horn would completely disappear. 
 And this is precisely what we find to be the case. 
 The earliest cervine animals, or those of the 
 Lower Miocene period, are absolutely hornless, 
 and the series is thus made complete. The ques- 
 tion naturally arises : Are these earliest hornless 
 forerunners of the true deer deer or antelopes? 
 The fundamental distinction between these two 
 groups of animals lies in the fact that the horns 
 of the antelope are hollow, instead of solid, as in 
 the deer, simple, instead of branched, and that they 
 are not periodically shed. But if there are no 
 horns present, how are we to determine, in the 
 absence of these distinguishing characters, the 
 
OF EVOLUTION. 
 
 actual position of the animal under consideration ? 
 This is a problem that does not admit of ready 
 solution ; indeed, there is a strong probability that 
 the hornless animals of the Lower Miocene period 
 were ancestral to both deer and antelopes, a dual 
 development starting out, just as we have seen to 
 be the case with many other animals, in diverging 
 directions. The high probability of this dual 
 development is forced upon us, apart from all 
 other considerations, by the remarkable case of 
 the prong-horn of the western plains, which is a 
 hollow-horned ruminant, to all intents and pur- 
 poses a true antelope, yet with divided horns, 
 whose sheaths are periodically shed, in the manner 
 of the shedding of the horns of the deer. 
 
 The deer have quite recently furnished one of the 
 most interesting examples of a connecting form, or 
 so-called missing link, in an animal exhumed from 
 the swamps of northern New Jersey, which stands 
 intermediate between the stag and elk. This 
 relation is made clear by the figures of the skulls 
 of the three species which are placed before you. 
 
72 THE GEOLOGICAL EVIDENCES 
 
 1, Skull of the Canada stag; 2, of Cervalces Americanus; 3, of the elk. 
 (After Scott.) 
 
OF EVOLUTION. 73 
 
 In the stag, it will be observed, the skull is high, 
 and shows but little of that anterior attenuation 
 which is such a distinctive feature of the skull of 
 the elk. The nasal bones (N) of the former, again, 
 are remarkably long when compared with the sim- 
 
 Head of Cervalces A mericanus. Specimen in the Museum of 
 Princeton College. 
 
 ilar bones of the latter, and the premaxillaries(pMx), 
 instead of being projected forward along the hori- 
 zontal plane of the base of the skull, are deflected 
 sharply downward. In all these points, it will be 
 seen, the newly discovered form (Cervalces) holds 
 
74 THE GEOLOGICAL EVIDENCES 
 
 an intermediate position. The skull exhibits a par- 
 tial attenuation anteriorly, the premaxillaries are 
 directed about equally downward and forward, 
 and the nasal bones are measurably contracted in 
 size. The horns likewise furnish characters which 
 further serve to establish this dual relationship. 
 
 There is still one phase of development which 
 remains to be considered the development of 
 intellect or brain force. Although seemingly an 
 intangible subject, geology affords evidence in re- 
 gard to it fully as important as that which attaches 
 to the development of bone or muscle. No abso- 
 lute relationship has as yet been determined to ex- 
 ist between the size of the brain and mental capac- 
 ity, the latter being largely, or even principally, 
 dependent upon the quality of the brain mate- 
 rial, but, in a general way, it may be admitted 
 that the larger the brain in proportion to the 
 body, the greater will be the amount of brain 
 force generated by it. Using this most legit- 
 imate standard as a basis for comparison, 
 
OF EVOLUTION. 75 
 
 we are brought to an astonishing result when 
 a study is made of the brains of the earlier 
 animals, the outlines of many of which have been 
 as perfectly preserved as the casts of the interiors 
 of shells. From this study it appears that all 
 the Tertiary mammals had comparatively small 
 brains, and that there has been a gradual increase 
 in the size of the brain mass from the earlier to the 
 later parts of this period, the increase being almost 
 wholly confined to the cerebral hemispheres. In 
 the earlier forms indeed, until late in the Terti- 
 ary the hemispheres left the cerebellum entirely 
 uncovered, and the olfactory lobes were corre- 
 spondingly largely developed. The brain was, in 
 fact, more nearly reptilian in character than mam- 
 malian. The series of diagrams before you illus- 
 trate the development of the brain in certain 
 mammals of the Tertiary period more or less 
 closely connected in their ordinal relations. 
 
 It wifl be seen from these figures that the 
 relative size of the brain in the older mam- 
 malian types was small when compared with 
 
76 THE GEOLOGICAL EVIDENCES 
 
 that of the forms which successively followed 
 them. In some of the Dinocerata, which were 
 by far the largest of the Eocene Mammalia, 
 nearly equalling the elephant in size, the brain 
 was so small that it could have been passed 
 through the neural arches of the lumbar or 
 
 1, Skull of Tinoreras (Uintatherium) ingens, with brain cast in position ; 
 2, of Dinoceras laticeps. Middle Eocene. (After Marsh.) 
 
OF EVOLUTION. 
 
 77 
 
 sacral vertebrae ! In relative size this diminutive 
 brain, which is proportionately the smallest brain 
 known among mammals, whether recent or fos- 
 sil, is surpassed by the brains of many reptiles. 
 Hoplophoneus oreodontis, one of the sabre- 
 toothed cats, although of about the size of a 
 panther, had a brain no larger than that of the 
 domestic cat. The peculiar sulci or gyri seen 
 
 3, Skull of Limnohyus robustus (tapiroid), Middle Eocene ; 4, Amynodon 
 advenus (rhinoceros), Upper Eocene. (After Marsh.) 
 
78 THE GEOLOGICAL EVIDENCES 
 
 on the dorsal aspect of the brains of modern 
 mammals were also largely absent in the 
 earlier forms, or were disposed longitudinally, 
 instead of transversely, as we find them in 
 the lowest of recent placental mammals the 
 rodents, edentates, and insectivores. The same 
 law of cerebral development which is here indica- 
 ted for the Mammalia is also applicable to reptiles 
 
 5. 6. 
 
 5, Skull of Elotherium crassum, Miocene ; 6, Platygonus compressus 
 (peccary), Pliocene. (After Marsh.) 
 
OF EVOLUTION. 
 
 79 
 
 and birds, and in probably equal degree. I have 
 placed before you a drawing of one of the lar- 
 gest of the dinosaurian reptiles, the Jurassic Bron- 
 tosaurus, an animal measuring probably fifty feet 
 in length, yet in which the weight of the entire 
 skull does not appear to have exceeded that of 
 the fourth vertebra of the neck. 
 
 7, Skull of Mastodon Americanus, Pliocene and Post-Pliocene. 
 (After Marsh.) 
 
8o THE GEOLOGICAL EVIDENCES 
 
 Before dismissing this part of my subject I 
 must direct your attention to one phase of the 
 inquiry which is as well geographic as it is geo- 
 logic in its scope. It is a familiar fact that the 
 different parts of the earth's surface are to-day 
 characterized by distinct faunal associations. 
 Thus, we recognize a South American fauna as 
 distinguished from an African, a Eurasiatic 
 fauna as distinguished from an African or Aus- 
 tralian, and so on. Now if, as is contended by 
 the upholders of organic evolution, our exist- 
 ing faunas have been developed from their 
 immediate faunal antecedents, we must have 
 some indication or foreshadowing in the latest 
 geological formations of the faunal characters 
 which, in a broad way, serve to distinguish the 
 several zoogeographical regions. And this is 
 precisely what we find. You have already 
 learned that in the earlier Tertiary periods of 
 mammalian history the existing animal forms 
 were almost wholly different from the forms of 
 to-day, and that they became less and less 
 
OF EVOLUTION. 
 
 81 
 
 (6) 
 
82 THE GEOLOGICAL EVIDENCES 
 
 different as we approached the modern era. But 
 with this distinctness there appears to have been 
 more of a general correspondence between the 
 faunas of the different parts of the earth's 
 surface, so that the zoogeographical boundaries 
 which we now recognize could at best be only 
 partially drawn. It is only in the Post-Pliocene, 
 or latest Tertiary, period that the approximation 
 between the past and recent faunas has been so 
 far established as to permit us to trace clearly 
 the existing zoogeographical relations, and to 
 state that the modern fauna has been sketched 
 out in place. Thus, in the Australian Post- 
 Pliocene marsupials Diprotodon, Nototherium, 
 Thylacoleo, and their allies, we have the fore- 
 runners of the various marsupial forms that now 
 characterize the continental fauna ; in the giant 
 birds Palapteryx, Dinornis, Mionornis, etc., from 
 New Zealand, Dromaeornis from Australia, and 
 ^Epyornis from Madagascar, the forerunners of 
 the wingless apteryx and the struthious birds from 
 the same or neighboring regions; and in the giant 
 
OF EVOLUTION. 83 
 
 South-American edentates, Glyptodon, Megathe- 
 rium, Mylodon, and their allies, the representative, 
 if not the ancestral, forms of the existing sloth, 
 armadillo, and ant-eater. 
 
84 THE GEOLOGICAL EVIDENCES 
 
 III. 
 
 There has been much speculation, and no less 
 controversy, during recent years, concerning the 
 birthplace and origin of man, and I don't know 
 that we are any nearer the solution of these 
 questions than we were immediately after the 
 publication of Mr. Darwin's " Origin of Species," 
 nearly thirty years ago. That man is a 
 descendant of some two-legged and two-armed 
 creature much like himself, although less homi- 
 nine both in the development of his intellectual 
 faculties and the structure of his bodily frame, 
 there is little reason to doubt, but science has 
 
OF EVOLUTION. 85 
 
 thus far failed to make known this earliest and 
 much looked for preadamite. I am not pre- 
 pared to share the enthusiasm of certain French 
 archaeologists who recognize in a number of 
 very ancient " chips " or " flints " the handiwork 
 of apes, and in these last the missing progeni- 
 torial tribe (Anthropopithecus) ; for although the 
 reputed facts may be true and I am far from 
 denying that they are true some further evi- 
 dence is needed before they can be confidently 
 accepted as facts pure and simple. Nor can I 
 fully appreciate the evidence which carries his 
 antiquity back to the earlier portion of the Ter- 
 tiary epoch. I fail to find satisfactory proof of 
 man's belongings having been found in deposits 
 very much (if at all) older than the Post-Pliocene, 
 although not unlikely some such will yet be 
 discovered of far more ancient date; but a sharp 
 line must be drawn between actualities and 
 probabilities. 
 
 In our own country the finding of the " most 
 ancient remains " of man has from time to time 
 
86 THE GEOLOGICAL EVIDENCES 
 
 been reported, but I am not aware that in any 
 case these remains can be proved to be older 
 than the remains found in different parts of 
 Europe ; indeed, in most cases they appear to 
 be much younger. The implements from the 
 " Trenton " gravels of the Delaware, if actually 
 belonging there, would seem to indicate an 
 antiquity dating from the glacial epoch, and 
 probably nothing beyond this can be definitely 
 located. The famous Calaveras skull, from the 
 auriferous gravels of California, is still too much 
 involved in obscurity to permit of its being 
 used in ^ positive evidence; nor can much 
 dependence be placed upon the calculations 
 which have been made to determine the age of 
 the man of Florida, which was discovered by 
 Pourtales upwards of thirty years ago. I have 
 the pleasure to lay before you this evening two 
 human vertebrae, which I obtained two winters 
 ago from a semi-compact ferruginous sandstone 
 on Sarasota Bay (west coast of Florida), and 
 which our distinguished President, Prof. Joseph 
 
OF EVOLUTION. 87 
 
 Leidy, has kindly determined for me to be 
 probably the last dorsal and first lumbar. The 
 vertebrae, it will be observed, are of iron, there 
 having been a complete substitution of the bony 
 material by iron-hydroxide (limonite), but with 
 an absolute retention of the structure distinctive 
 of bone. Many of the other bones of the skel- 
 eton were still associated with these vertebrae, 
 but with limited facilities at my command I was 
 only able to procure these two fragments. How 
 old they may be I am not prepared to say ; 
 unfortunately, their geological position was such 
 as not to permit of a clear determination of this 
 point. Apart from the cast of an unknown 
 form of coral found in a neighboring and 
 similarly placed stratum, paleontology furnishes 
 no clue to the solution of this interesting prob- 
 lem. But that the age is very great, the 
 condition of fossilization fully proves; and I think 
 it may be safely held that the vertebrae in ques- 
 tion represent the most ancient, or very nearly 
 the most ancient, remains of man that have thus 
 
88 THE GEOLOGICAL EVIDENCES 
 
 far been discovered. But beyond this it would be 
 dangerous to venture. 
 
 We have thus far confined our attention 
 exclusively to a consideration of the higher 
 groups of animals, the Vertebrata. The lower 
 or invertebrate animals present equally striking 
 proofs of modification and transformism, but the 
 limited time at my command will permit me 
 to bring before you only one or two special 
 cases, drawn from the class of Mollusca, with 
 which my own investigations are connected. If 
 the doctrine of evolution holds true, it stands 
 to reason that, as in the case of higher animals, 
 the existing fauna must be foreshadowed in 
 the fauna of a period immediately preceding ; 
 this connection cannot generally be established, 
 owing probably to migrations and intermixtures 
 of different faunas, as depending upon changes 
 in the physical condition of the surroundings. 
 In the sheltered region' of the Gulf of Mexico, 
 
OF EVOLUTION. 89 
 
 however, a fauna appears to have been 
 developing in place for probably hundreds of 
 thousands of years, so that the unequivocal 
 ancestors of many of the living forms can be 
 found in the fossil remains that preceded them. 
 I have brought before you several such forms, 
 which it was my pleasure to discover two win- 
 ters ago in the interior wilds of the peninsula 
 of Florida. 
 
 One of these you will readily recognize as a 
 wing-shell, of the type of the large pink 
 conch which is found on so many of our 
 mantel tops ; I have named the species, in 
 honor of the distinguished President of this 
 Academy, Strombus Leidyi. Alongside of it I 
 have placed the stromb most nearly related to 
 it in the recent fauna, Strombus accipitrinus, an 
 inhabitant of the Floridian and West Indian 
 coasts. In comparing the two together it will 
 be seen that the principal distinguishing charac- 
 ters lie in the particular form of the wing, and in 
 the tuberculation of the body-whorl or chamber, 
 
90 THE GEOLOGICAL EVIDENCES 
 
 but these differences are so well marked as to 
 obscure at first sight the relationship. In the 
 majority of the fossil forms the wing is more 
 or less evenly crescentic in outline, whereas in 
 the recent species it is markedly quadrangular 
 in its upper moiety, so much so that in extreme 
 specimens the outline is wholly different from 
 that seen in the fossil. But Strombus Leidyi 
 shows a pronounced tendency to vary in the 
 direction of 5. accipitrinus, and conversely the 
 latter, in this regard, seems to vary equally in 
 the direction of the former, so that we have 
 an almost perfect gradation established between 
 the extreme wing-structures seen in the one 
 species and the other, or between the almost 
 perfectly crescentic outline and that which 
 exhibits the greatest quadrangulation. In a 
 similar manner the very prominent tubercles 
 seen in the recent species, which are represented 
 by elongated nodes in the fossil, are more or 
 less lost in some individuals, although they at 
 all times appear more prominent than in the 
 
OF EVOLUTION. 91 
 
 fossil ; on the other hand, the nodose ribs of 
 the fossil frequently tend in the direction of 
 tuberculation, thus again bridging the interval 
 between the two species. We have step by step 
 all the intervening gaps filled in between the 
 two species, and in such a manner as to leave no 
 doubt concerning the interrelationship of the 
 forms in question. It is interesting to note in this 
 connection that no individuals of the recent 
 form occur in the deposits containing the fossil 
 species, which, as an inhabitant of the seas 
 immediately preceding the present one, may 
 very reasonably be looked upon as the imme- 
 diate progenitor of the stromb of the modern 
 Gulf. 
 
 In the case of the other two forms which I 
 have brought before you, the fossil crown-conch 
 (Melongena subcoronata) and volute (Valuta 
 Floridand), we have similar or analogous details 
 of structure which unite them with their living 
 representatives (Melongena corona, Voluta Junonid). 
 Thus, the first-named is distinguished from the 
 
92 THE GEOLOGICAL EVIDENCES 
 
 common crown-conch of the Gulf by several 
 well-marked characters, of which the deficiency 
 in the number of tubercles to the different 
 whorls, and the horizontal position occupied 
 by them, are especially apparent. The tuber- 
 cles are also more compact, and do not 
 show the foliaceous or scaly character which 
 they exhibit in the living species. But while 
 these differences in structure readily serve to 
 distinguish the typical or most abundant forms 
 of the two species, they in a measure fail when 
 some of the less typical forms are taken by 
 way of comparison. Thus, a tendency toward 
 increase or duplication in the number of 
 tubercles is here and there apparent in the fossil 
 form, while, per contra, a tendency toward 
 deficiency is not exactly rare in the recent 
 species. Similarly, the tubercles or nodes of the 
 fossil, which in the typical forms stand out 
 nearly horizontally from the shoulder of the 
 shell, or have but a moderate inclination, are 
 occasionally more nearly directed in the position 
 
OF EVOLUTION. 93 
 
 occupied by the tubercles of M. corona ; 
 conversely, in many of the less typical forms of 
 the latter there is a close approximation to the 
 condition found in M. subcoronata. In this 
 manner the two species are inseparably bound 
 together. As in the case of the stromb, so in 
 this instance also, no trace (or at best but 
 a doubtful one) of the recent Melongena has 
 been found in the deposits containing the fossil; 
 nor, on the other hand, have any traces of the 
 latter been found in the modern seas, so that we 
 may here also plausibly assume that the one form 
 is the forerunner and probable progenitor of 
 the other. 
 
 The fossil volute differs slightly in outline 
 from the rare living species of the coast, and is 
 further distinguished from it by its more acute 
 apex, and the greater prominence of the costal 
 ornamentation on the apical portion of the shell. 
 These differences, although not very great, nor 
 seemingly of much consequence, are yet per- 
 sistent, and as such may be considered of 
 
94 THE GEOLOGICAL EVIDENCES 
 
 sufficient value to characterize a distinct species. 
 But despite these differences it is impossible not 
 to observe the very close connection which 
 unites the two forms, and I must admit that on 
 first finding the fossil I almost unhesitatingly 
 referred it to the recent species (Valuta Junonid], 
 and only after a careful comparison of actual 
 specimens of the two species was I able 
 to discern the - permanent differences between 
 the forms in question. Yet so fully convinced 
 was I of the ancestral relation binding together 
 the two that I did not hesitate, even in the 
 absence of all color-markings, to pronounce 
 the one as the all-probable progenitor of the 
 other. Other specimens that have since come 
 to me prove the correctness of my surmise, 
 since these very clearly show the peculiar and 
 beautiful color-markings which belong to Voluta 
 Junonia. 
 
 I also place before you two series of conch- 
 shells of the group to which the pear-conchs 
 (Fulgur and Sycotypus) of the New Jersey coast 
 

 6a 
 
 1-5, Series connecting Fulgur pymm with Falgur canaliculatus. 1, la, b and c, Fulgur pyrun 
 
 7, V. Junonia 8, 8a, Melonge 
 
Sa 
 
 excavatus. 3, F pyriformia. 4, F. plagoaud 5, F. canaiicuiatus. 6, 3a. Voluta B'loridana 
 
 coronata. 9. M. corona. 
 
OF EVOLUTION. 95 
 
 belong, which the fossil fauna of Florida has 
 permitted me to complete. They range back in 
 time from the present era to the Miocene, or 
 possibly even a still older, period, and comprise 
 each some four or five hitherto described species 
 and two or three new forms which are now for 
 the first time brought to light. In other words, 
 they represent some six or seven distinct species 
 of systematists, yet so closely do they grade 
 one into the other that it is impossible to 
 define the individual limits, and they may be 
 properly considered to represent one true or 
 varying type. Is not this a remarkable instance 
 of specific variation and origination, or is it 
 merely a matter of blind coincidence ? 
 
 It might very naturally be contended that in 
 assuming the Pliocene fossils here represented 
 to be the ancestral forms of some of the living 
 species the assumption is in the nature of a 
 thing taken for granted, and that no reasonable 
 proof has been presented indicating the neces- 
 sary changes from the extinct to the recent 
 
96 THE GEOLOGICAL EVIDENCES 
 
 faunas. And were no further evidence presented 
 than that which is embodied in the three shells 
 under consideration, the objection taken would be 
 allowed full weight. But when it can be shown, 
 as can very readily be done in the present 
 instance, that the Pliocene Floridian fauna, which 
 is in geological time the fauna immediately pre- 
 ceding the present one, already embraces many 
 of the forms that are now living, and a host of 
 others that are strictly representative of, although 
 not identical with, living forms ; and further, 
 that some of the forms, as the strombs, exhibit a 
 remarkable tendency to variation or convergent 
 modification, the objection loses all force, since 
 it is distinctly opposed to the interpretation of 
 fact and common sense. Manifestly, paleon- 
 tology can offer no direct testimony to trans- 
 mutation beyond that which a common-sense 
 interpretation of facts will allow. But the evi- 
 dence is approximately of the same nature as 
 that which permits us to interpret a very large 
 proportion of the phenomena about us without 
 
OF EVOLUTION. 97 
 
 our being able to perceive the workings of such 
 phenomena. 
 
 I cannot conclude this chapter on molluscan 
 variation without referring to the very remarkable 
 discoveries which have been made during the 
 last few years in some of the later Tertiary lake 
 basins of Germany and Austria, bearing upon the 
 modification, through time, of the characters of 
 certain well-known freshwater genera of mol- 
 lusks. The so-called " Paludina beds" of Slavo- 
 nia, which date from about the middle Tertiary 
 period, will best illustrate my purpose. From 
 these deposits, which run continuously from what 
 are known as the " lower " to the " upper Paludina 
 beds," and whose physical development appears 
 to have been practically unbroken, Prof. Neumayr, 
 of Vienna, has brought to light a number of 
 forms, eight or more, of Paludina, which differ 
 so materially from one another that to the casual 
 observer they appear like so many distinct 
 species ; and as such have they actually been 
 
 described. But it has been shown that the 
 
 (7) 
 
THE GEOLOGICAL EVIDENCES 
 
 divergences through which the different forms have 
 been brought about are clearly continuous and 
 
 Successive varietal and specific forms of Paludina from the Tertiary 
 ''Paludina-beds" of Slavonia. (After Neumayr.) 
 
 progressive; in other words, that the modification 
 is a gradual one, leading up from the oldest 
 
OF EVOLUTION. 99 
 
 found form of the basal series to the newest 
 from the top bed. This is one of the completest 
 cases of transformism known in the animal king- 
 dom. 
 
 I have now submitted to you such of the 
 evidences bearing upon evolution as it appeared 
 to me would most readily appeal to a quick 
 understanding and an unprejudiced mind. It 
 is, however, but a tithe of the evidence which 
 geology offers, and but a mere figment of that 
 which pertains to zoology. If the facts that I 
 have placed before you are true, and are prop- 
 erly interpreted, they must be held to be con- 
 clusive in favor of evolution ; if they mean noth- 
 ing, then science is a delusion and a snare, and 
 we will be compelled to begin anew our conception 
 of the universe, since the greater number of the 
 recognized truths of astronomy, of chemistry, 
 and of physics are based on facts identical in 
 character with those which I have adduced from 
 geology and paleontology. 
 
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