18 
POPULAR SCIENCE NEWS. 
[Februart, 1891. 
receive their education from external nature. Soil, 
climate, heat, moisture, altitude, position, food, 
furnish conditions under which they become 
healthier, larger, stronger, or the reverse. When 
the change in external conditions is considerable 
and long continued, what we call varieties are 
produced, and during longer periods new species 
are also developed. An orgaliism would not 
change as long as the external conditions remained 
the same ; but when these change, it must change 
or die. Some plants may be grown either in water 
or in soil, but the changes produced by changing 
them from one element to the other are so great 
that they may be taken for distinct species. Arti- 
ficial selection illustrates the more slow and patient 
work of natural selection. Breeders of rabbits 
produce what color they prefer by careful selec- 
tion. Nature has done the same thing. Quite 
black or white rabliits can be more easily seen by 
their enemies, and would have less chance of 
escape. They have therefore died out. The grey 
rabbit— i. e., the Attest — has survived. 
Natural selection means that those organisms 
which can adapt themselves to external changes, 
themselves change and survive ; the others perish. 
Now no two organisms are ever alike. Infinite 
variety reigns through nature. The offspring of 
the same parents vary. No two individuals are 
quite alike. Some are better adapted to the 
changes which may be taking place than others. 
They may be stronger, fleeter, or of more suitable 
color. Evolution produces these peculiarities, 
and natural selection takes advantage of them. 
It may be said that evolution produces new forms, 
and natural selection preserves them. Every 
organism possesses a certain potentiality for 
change, and the extent of any change it undergoes 
is measured by this potentiality and tlie extent of 
the external influences. Will this change always 
be in an upward direction, from lower to higher 
forms? It does not follow that it should, and 
nature teaches that it may be either progressive 
or retrogressive. • 
The theory of evolution explains many facts 
which are otherwise inexplicable, and intense 
excitement in the scientific world has attended its 
study and application to living forms, chiefly those 
of the animal kingdom. A field for investigation 
less explored, but of great interest, exists in tlie 
vegetation of the primeval world. The animal 
remains preserved in the rocks are chiefiy bones, 
teeth, or shells — the harder parts of the animal 
structures. They are not such as teach us any- 
thing of the nervous, reproductive, or digestive 
systems of the animals then existing. But in 
regard to the vegetable kingdom, we have the 
most delicate organisms preserved. Leaves, 
stems, roots, fruits, seeds, and spores are found 
In the most perfect state of preservation. The 
artificial changes brought about l)y the inter- 
ference of man with the growth and development 
of animals and plants, are rapid, and therefore 
unstable, while those of nature are slow and more 
permanent. For the demonstration of the truth 
of the theory of evolution, unlimited time is 
required. The changes it implies are the result 
of the slow operation of physical causes during 
ages so vast that, in comparison, the historic 
period is an insignificant point of time. The 
human remains and the cats and crocodiles which 
were embalmed by the Egyptians, prove that the 
3,000 years that have elapsed since they lived are 
utterly inadequate to bring about sucli results. 
While, therefore, the facts presented by animal 
and vegetable organisms existing on the earth 
today are inexplicable on any other theory, the 
" testimony of the rocks " is required to complete 
the demonstration that evolution is something 
more than a splendid and ingenious hypothesis. 
Herbert Spencer has been disinclined to grant 
that the records in the rocks afford sufficient evi- 
dence on which to base an opinion ; but increasing 
geological knowledge warrants the opinion of 
other liigh authorities that the stories written 
there — although the continuity is often inter- 
rupted — are sufficient to give us a clear percep- 
tion of what the course of nature has been. Tlie 
crust of the earth for a considerable deptti is com- 
posed of series of rocks which have been formed 
under water. These stony archives contain the 
remains of animal and vegetable forms, which are 
the only relics we have of the biology of the 
earth's early days. Some of these series of rocks 
are many thousands of feet in thickness, repre- 
senting incalculable periods of time. The verj' 
lowest of these series — the Laurentian, .S0,000 feet 
in thickness — contains no fossil plants. The next 
series — the Huroniau, 18,000 feet thick, and the 
Cambrian, 15,000 feet thick — yield only a few- 
traces of vegetable life. Little more can be said 
of the next series, — tlie Silurian, .32,000 feet thick, 
— in which have been foimd chiefly a few spores 
of doubtful character. It is the next series — the 
Devonian beds — that first afTords evidence of luxu- 
riant vegetation. One deposit in this series — the 
old red sandstone — lias been made classical by the 
labors of Hugh Miller. In I^ngland, in Ireland, 
and in New Brimswick these beds contain mag- 
nificent fossil remains. 
If evolution necessarily meant the development 
from lower to higher forms, the evidence aftbrded 
by the vegetation of the ancient world would not 
be entirely satisfactory. As we ascend through 
the later rocks referred to, the fomis diminish in 
size. Club mosses, sucii as abound in the forests 
of South America and New Zealand, were forest 
trees in ancient times ; and plants which appear 
as forest trees in the Peuniau beds, have dwindled 
into lower forms. Instead of developing into 
higher forms, we see evidence of a change into 
lower. We have no evidence to show that the 
forest trees of tlie present day have been developed 
out of the gigantic forms which flourislied in the 
forests of the ancient world, and they have possi- 
bly lieen developed out of otlier and inferior 
forms. The theory of evolution is consistent witli 
development in either direction. Ferns furnisli a 
remarkable example of plants that have undergone 
little or no change, except in size, from the time 
when the coal measures were formed till the pres- 
ent day. Underlying the Carboniferous* series, 
they are found as tree ferns in the oldest Devonian 
rocks, /rhey abound in the coal measures and in 
the Oolites, and survive in tlie forests of New 
Zealand and the central parts of America, and, 
except in size, appear to have undergone no 
change through all these long ages. ITie contrary 
is true in reference to tlie conifers, or cone-bearing 
plants. In the coal measures trunks of these trees 
have been found more than forty-four feet in 
height. ITiey were more nearly allied to the 
Araucanian or Norfolk Island pines than to Euro- 
pean firs. They appear to have undergone a 
gradual change till we reach the Cretaceous series 
of rocks, but have changed very little from then 
to the present day. The cj^ads do not appear till 
the Triassic Age, long after the coal measures 
were formed, and they cannot be traced back to 
any forms found in the Carboniferous beds. In 
the Oolitic rocks they appear in vast numbers and 
magnificent forms, and seem to have covered the 
globe from north to south. , They occur in the 
Cretaceous beds, — the latest of the Secondary 
formations, — but in the Tertiary beds their mag- 
nificent forms disappear. Their modern repre- 
sentatives, the eyas and zaraia, still linger in the 
southern hemisphere, in a narrow line which 
bounds the outside of the tropical zone. Of flow- 
ering plants, monocotyledons and dicotyledons, 
there were scarely any traces in the Oolites, and 
only a few in tlie Cretaceous lieds. ITiese and the 
earlier formations represent innumeralile ages, 
during which the earth had lieen devoid of any 
plants with whicli we associate the idea of bloom. 
It is only wlien we reach the Tertiary period tliat 
they are found in abundance. In these later beds 
twenty-five or more orders of these plants have 
been found, including the palm, walnut, maple, 
willow, liawlhorn, almond, plum, and the meadow 
sweet, showing an approximation to the trees of 
the Post-Tertiary or modern period. 
Tills brief glance at the vegetation of tlie ancient 
world may remind us tliat a martied dift'erence ig 
shown between the development of plants and the 
development of animals. The animal kingdom 
exliibits a high stage of development at an early 
period. Vertebrate animals — fishes of the liigheat 
organization — are found in tlie upper Siluriau 
rocks. The family of sharks stands at the head 
of the order of fishes, and the first fossil fislies 
found are not only sharks, but sliarks of tlie high- 
est order — such as the Port .Jackson sliarks. Yet 
probably 120,000 feet or 1.30,000 feet of rocks must 
be passeil througli before the most liiglily oigan- 
ized plants make tlieir appearance. Assuming, as 
a general fact, that tlie thickness of any series of 
rocks is indicative of the relative lengtli of time 
tliat must be assigned for their formation, it 
appears that tiie liighest forms of vegetable life 
did not appear till a comparatively late period in 
the world's history, and then they appeared sud- 
denly and in great abundance. Nine-tenths, or a 
still greater proportion, of the immense cycles of 
time required for the formation of the earth's 
crust had passed away before tlie liigliest vege- 
table forms appeared. It is scarcely surprising to 
find that this jieriod of magnificence and abun- 
dance in the vegetable kingdom is also marked by 
a corresponding display of animal life. Lions, 
tigers, eleptiants, and mammoths flourished in the 
middle Tertiary period, and the earth seems to 
have possessed the same great variety of ,'iiiiiiial 
forms whicli characterizes it today. The sudden 
outliurst of the highest forms of visgetable life is 
a significant fact, the fuller meaning of which 
furtlier geological researches may reveal. It must 
be borne in mind that the researciies of geologists 
have been pursued over a comparatively small 
portion of the eartli's surfaw, and investigations 
in other <iuarters of the globe may bring to light 
facts to show that the appearance of abundant 
higlily organized vegetation was less phenoininally 
sudden than it now appears to have lieen. It is 
also to be remembered that the immense denuda- 
tion which we know to have gone on, may have 
removed deposits which would have furnished 
evidences of more gradual development of vege- 
table forms than the known records of the rocks 
now present. 
A survey of the present condition of life on the 
globe and the revelations of geology warrants the 
conclusion that the difficulties which the theory 
of evolution is inadequate at present to solve, are 
insignificant compared with the beauty and order 
which all nature assumes in the light of its teach- 
ings. Every living form tends to vary, more or 
less, from its original type. Nature loves infinite 
variety. Every living form is also capable- of 
adapting itself, in a greater or less degree, to 
changed conditions. ITiose forms which vary in 
the most suitable direction, and are able most 
