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Full text of "The geological evidence of evolution"

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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