Vol. XXV. No. 1.] 
POPULAR SCIENCE NEWS. 
3 
under tlio inliueiice of sunlight, is able to make 
chlorophyl. 'I'liat is to say, the light of the sun sets 
up certain molecular changes in the protoplasm 
and a product of these reactions in vital chemistry 
is chlorophyl. Chlorophyl once nuide, the proto- 
plasm is able to cany forward certain other 
processes in constructive chemistry. It is able to 
take simple stable compounds, like carbonic acid, 
,water, and ammonia, and make of them complex 
compounds, like starch, sugar, oils, etc. These 
products may then go to the making of new pro- 
itoplasm — to the nourishment and growth of the 
protoplasm of the cell, and to the formation of 
new cells. 
These processes in plant physiology — al)out the 
exact nature of which, it will be observed, we 
know very little — are of fundamental importance 
in the general economy of organic nature. For it 
is in this way tiiat the inert matter of tlie inor- 
ganic world — gases, liquids, and earthy salts — is 
built up by the light and heat of tiie sun into 
energy-bearing compounds that serve as food for 
the members of the organic kingdom, 'lluis the 
chlorophyl bodies, as the minute bits of green- 
stained protoplasm of plant cells are called, are a 
wonderful intermedium between the living and 
the lifeless kingdoms in nature. 
Tbe little desmid, theref<u-e, nourislies itself in 
the same way as higher plants. It takes in raw 
materials from the iuorganic world and builiis 
them up into highly complex, energized com- 
pounds, which aft'ord food for the ever active pro- 
toplasm. Having thus seen how the desmid 
carries on the function of nutrition, let us next 
notice how the other fundamental physiological 
function — that of reproduction — is efTected. It is 
by the process common to all the lowest forms of 
■ life, both plant and animal, namely, by self- 
division. In M. radiosa the constriction noticed 
above deepens until it has formed a complete sep- 
ttun, cutting the protoplasm into two parts. 
These gradually become rounded and indented, 
until precisely like tlie parent plant. After a 
while they give rise to anotlier generation by the 
same process of self-division. 
It appears, liowever, that tliis process alone is 
not sufticient to perpetuate the species. At times, 
especially at the approach of cold wcuither in late 
summer, another method of reproduction takes 
place. Two cells having come into contact and 
. opposition, the contiguous parts of tiieir cell walls 
thin away and finally break through and allow an 
interconmiunication of the jirotoplasm. The sun- 
dered envelopes then unite, and thus a cell is 
formed from the original two. This cell remains 
in an inactive condition (resting stage) for some 
time, probably till the next spring. It tlien gives 
rise to new plants by a process of self-division. 
It seems scarcely questionable that this method of 
reproduction, called conjugation, is a sexual one. 
We know that the principle of sexuality holds 
true for plants as strictly as for animals. In a 
high plant a seed is fomied only when an ovule 
(female cell) comes into union with a pollen grain 
^male cell). It is very probable that among low 
plants, as the desraids, tlie two cells that conjugate 
re likewise sexually different. It is true that the 
|wo cells ajjpear to be quite alike in physical char- 
picters ; it would seem as if their union could pro- 
8uce nothing more than a new cell of the same 
nature, different only in the nnitter of being twice 
1 large. But we cannot judge of the ])oteucies of 
hese cells by their physical appesu-ance. They 
lay be, and in all likelihood are, essentially difter- 
fent in the quality of sex, and by their union is 
Bected a recuperation of the native reproductive 
ower of tlie protoplasm. 
It remains to notice that desmids possess the 
power of locomotion. The little plant is seen to 
move very slowly onwards,,or witli an oscillating 
movement backwards and forwards. IIow the 
movements are eft'ected is not known : no one has 
been able to discern special organs of locomotion, 
as cilia, or vibrating hairs, possessed by many 
one-celled organisms, both plants and animals. 
It is probable that their movements are conse- 
quent upon vital acts, taking place in the proto- 
plasm. 
Uniov College, Schenectadt, X. Y. 
[Original in Popular Science News.] 
GEOLOGICAL FOKM.VTIOX OF THE EARTH 
—ITS EVOLUTION FROM CHAOS TO ORDER 
—RELATIVE AGE OF FOSSILS. 
BY JOSEPH WALLACE. 
The interesting and searching discoveries in 
fossils, which were looked upou a century ago as 
a burden to the mineralogist, soon became an im- 
portant auxiliary to geology and a valuable aid to 
natural science. The hypothesis which was ac- 
cepted by many of the learned in i-egard to the 
Flood, gradually gave way to more reasonable 
opinions as they progressed in their discoveries. 
The perished animals and plants, referred to in 
our last article, which floated together were not 
luixeil together, but rather in quite a determined 
distribution. FrequentI}' in one laj'er plants and 
remains of animals were well preserved ; in the 
other, one could only discover with the greatest 
dittieulty few and hardly recognizable traces of 
organic life. Here an exuberant flora arose, there 
a numerous fauna, in those layers were promi- 
nent bones ol land and mauimifers, in which the 
denizens of the deep were vastly more numerous; 
now, mollusks. then membranous aidnuils ; and 
to thi^ fishes and amphiliia, vertebrates were 
added. In one place, one could And forms which 
seemed to indicate (juite a ditterent world ; in 
another, he could see a more or less approaching 
to the present world, and kinds which now popu- 
late both land and water. 
With the development of geology, it became a 
particular matter of fact, that the greater number 
of the species of the fossil animals and plants did 
not live v\ith man : that the lower and oldest lay- 
ers contained species which are wanting in the 
upper and youugest ones. All these things were 
uufavoi-able to those who held the Flood hypothe- 
sis. The results of the researches demanded 
longer periods of time for those species which died 
out: and from the situation and eml)edment of the 
fossils, one could, in some places, draw conclu- 
sions with greater certainty, that the excellent 
preservation of the aidmal and vegetal)le forms 
were only the consequence of a slow, (luit^t, pro- 
gressive petrifactive process. 
Slowly but surely the dawn of light was break- 
ing o^'er the horizon of darkness; there was no 
more doubt among geologists that the slimy sedi- 
ments which had destroyed this animal and vege- 
table world, and those of the Flood, wen^ quite 
two dift'ereut things. They recognized that the 
formation of the earth was yet far from being 
completed when the first organism had already 
arisen; and the dispute between Xeptunists and 
Plutonists was decided with regard to the strati- 
fled rocky regions. There, where organic beings 
had lived, the destroying power of Are was ex- 
eluded. 
Relative Value of the Or/janic Remains. — As the 
conditions for the preservation of organic remains 
exist more favorably under the sea than on land, 
marine organisms must be far more abundantly 
conserved than those of the land. This is as true 
today as it was in past geological periods. Hence, 
for the purpose of the geologists, the fossil re- 
mains of marine f onus of life far surpass all others 
in value. .4mong them there will necessarily be a 
gradation of importance, regulated chiefly by their 
relative abundance. Xow, of all the marine tribes 
which live within the juxta-terrestrial belt of sed- 
imentation, unquestionably the moUusca stand in 
the place of prominenee as regards their aptitude 
for becoming fossils. In the first place, they 
almost all possess a hard, durable shell, capable of 
resisting considerable abrasion, and readily pass- 
ing into a mineralized condition. In the next 
place, they are extremely abundant both as to in- 
dividuals and genera. Moreover, they appear to 
have possessed those qualiflcations from early 
geological times. Happily for science, we have in 
the marine mollusca a common ground of compar- 
ison between the stratified formations of dilTerent 
periods. They have been styled the alphabet of 
paleontological inquirj' and the medals of creation. 
It will be seen, further on, how much in the inter- 
pretation of geological history depends upon the 
testimony of sea-shells. 
Looking at the organisms of the land, we per- 
ceive that, as a rule, the abundant terrestrial flora 
has comparatively a small chance of being well 
represented in a fossil state, and only tliat portion 
of it — the leaves, twigs, flowers and fruits, which 
find their way to lakes by storms and other 
causes— is likely to be partially preserved. Ter- 
restrial plants, therefore, occur rarely among 
stratified rocks, comparativelj- speaking, and fur- 
nish only limited means of comparison between 
the foi-mation of difterent ages and countries. Of 
land animals, the vast majority perish and leave 
no permanent trace of their existence. Predatory 
and other animal fomis, whose remains may be 
looked for in caverns oi- peat morasses, must occur 
more uumiu'ously in the fossil state than those of 
birds ; consequently, they are correspondingly 
more valuable to the geologist for the comparison 
of difterent strata. 
Relative Age of Fossils. — Although absolute dates 
cannot be found in geological chronology, as 
already stated in a recent issue, it is not ditflcult 
to determine tlie relative age of diflTerent strata, 
and, conse(juently, of their enclosed organic re- 
mains. For this purpose the fundamental law is 
based on what is termed the " order of superposi- 
tion." This law may thus be defined : In a series 
of sti-atifled formations the older must underlie the 
younger. It is not needful we should actually see 
the one lying above the other. If a continuous 
conformable succession of strata dips steadily in 
one direction, we know that the beds at the one 
eud must underlie those at the other, because we 
can trace the whole succession of beds between 
them. Rare instances occur where strata have 
been so folded by great terrestrial disturbance, 
that the younger are made to underlie the' older: 
but this inversion can usually be made quite clear 
from other evidences. The true order of superpo- 
sition is decisive of the relative ages of stratified 
rocks. 
Accordingly, if formations lie regularly above 
each other, — R upon A, C upon B, D upou C, and 
so on, — it is evident that the organic remains found 
in A must have lived and died before those in B 
were entombed ; the latter must have been covered 
up before those in C, and likewise again, before 
those in D. The chronological sequence of fossils 
must be determined, first of all, by order of super- 
position of their enclosing strata. Tliere is noth- 
ing in the fossils themselves apart from experience, 
to fix their date, unless, for example, we knew 
