Vol. XXV. No. 2.] 
POPULAR SCIENCE NEWS. 
19 
easily to change In obedience to external Influ- 
ences, survive. Xature selects the Attest ; the 
rest gradually pass away. Tlie fauna and flora 
which adorn the earth today are the successors of 
sunilar systems which, in infinite variety, have 
been produced by slow changes, such as are now 
operating, and have been in ceaseless operation 
ever since life first appeared onthe globe. 
[Original in Populak Science News.J 
( ;K0L0GICAL DEVE1.0PMENT— use OF FOS- 
RSILS IX GEOLOGY. 
BY JOSEPH WALLACE, 
ij some of the preceding articles much space 
s given to fossils, as a great deal of misunder- 
. I standing still exists in regard to them. We hope 
I that what we have written is so clear and com- 
; prehensive that the student in paleontology will 
j have no trouble in fixing on his mind their nature, 
! their distinctive marks, their relative position, and 
ri their value to geology. In this, our last article 
on the subject, we will conclude with the "Use of 
Fossils in Geology." 
lliere are two main purposes to which fossils 
may lie put in geological research : 
First : To throw light upon former conditions 
lit physical geography, such as tlie presence of 
1 1 land, rivers, lakes, and seas in places where they 
(J do not now exist, change of climate, and former 
i' distribution of plants and animals. A few ex- 
amples will sufBce to ^low the manifold assistance 
which fossils furnish the geologist in the elucida- 
tion of ancient geography. Former land surfaces 
Mi-e revealed by the presence of tree stumps in 
. i their position of growth, with their roots brauch- 
' ing freely in their underlying stratum, which, 
nprescutiug the ancient soil, often contains leaves, 
fruits, and other sylvan products, together with 
pieces of bone, remains of insects, land shells, etc. 
Ancient woodland surfaces of this kind are found 
l>etween tide marks, and even below water line, 
^ : around diflerent parts of the British coast, and 
1 1 they unquestionably prove the subsidence of the 
land. Of more ancient dates are the "dirt beds'" 
of Portland, which, by their Uyers of soil and 
tree stumps, show that cycles of woodlands sprang 
lip over an upraised sea-bottom, and were buried 
j beneath the silt of a river or lake. Still further 
back in geological history arose the numerous 
I coal growths of the Carboniferous perio<l, point- 
ing to wide jungles of terrestrial or aquatic plants 
—like the modern mangrove swamps — that were 
j submerged and covered with sand and silt. 'I'he 
( former existence of lakes can tie satisfactorily 
1 1 proved from beds of marl or lacustrine limestone 
full of fresh-water shells, or from fine silt with 
leaves, fruits, and insect remains. Such deposits 
are abundantly forming at the present day, and 
i I they occur at various horizons among the geo- 
logical formations of past times. Tlie well-known 
nagelllue of Switzerland, a mass of conglomerate 
attaining a thickness of 6,000 feet, can l)e shown 
from its fossil contents to be essentially a lacus- 
trine formation. We may also derive a good deal 
iif information about tlie distribution of land, 
water, climate, and so on, from the position and 
nature of the separate strata and their organic 
lemains; but all this information must be very 
untrustworthy, on account of the incompleteness 
and uncertainty of the m.aterials on which the 
premises are founded. The maps which have 
lieen drawn of the different parts of the; earth's 
surface as it appeared in the earlier periods, must, 
ill many cases, be considered as merely hypotheti- 
lal sketches. ITie animals that were attached to 
the ground— banks of shells, for instance— were 
destroyed by gradual deposit of the surrounding 
strata; in other cases, sudden events — such as 
changes in the sea level, escape of gases, etc. — 
seemed to have killed hosts of animals. A vol- 
canic outljurst in the middle of the sea, recently 
observed near Sicily, killed an immense number 
of sea animals around it. Similar events no doubt 
caused the destruction of animals which we find 
petrified in masses, although it is believed they 
could have escaped. Bucklaud, speaking on the 
discovery of fossil fishes, observes: "The cir- 
cumstances under which the fossil fishes are 
found at Monte IJaldo, seem to indicate tliat they 
perished suddenly on aiTiving at a part of the 
then existing seas, of which the adjacent basaltic 
rocks aftbrd abundant evidence. The skeletons of 
these fish lie parallel to the laminae of the strata 
of the calcareous slate. They are always entire, 
and so closely packed on one another that many 
individuals are often contained in a single block. 
All these fishes must have died suddenly on this 
fatal si)ot, and have been speedily buried in the 
calcareous sediment then in the course of deposi- 
tion. From the fact that certain individinils have 
even preserved traces of color of their skin, we 
are certain that they were entombed before the 
decomposition of their soft parts had taken place. 
In the same manner we may imagine also deposits 
from muddy water, mixed, perhaps, with noxious 
gases, to have formed by their sediments a suc- 
cession of thick beds of marl and clay, and at the 
same time to have destroyed the testacea and lower 
orders of marine animals within the region thus 
invaded." 
Second : Another main purpose to which fossils 
may be put in geological research is to furnish a 
guide in geological chronology, whereby rocks 
may be classified according to relative date, and 
the facts of geological history arranged and 
intei-preted as a connected record of the earth's 
progress. But fossils have become useful to 
natural science in another way, as they teach us 
about plants and animals which have existed on 
the earth, but, for the most part, do no longer 
exist. Tlie history of the present animal and 
vegetable world is supplemented by that of the 
flora and fauna of the primeval world, and natural 
history thus becomes complete. As we have writ- 
ten about the "order of superposition" in strati- 
fled foi-matious in a recent number of Popular 
Science News, and of the "former and present 
fauna and flora*' in a fonner issue, there is no 
occasion for repetition. 
But the word "fossil" often conveys to our 
minds another idea: the remains of plants and 
animals tielonging to the primeval world. So the 
bones of species of animals now existiiig^that is, 
the present races of dogs, sheep, and cattle — 
would not be called fossils, even if they were 
found petrified or buriecl in strata. Tliis is sup- 
ported by such eminent scientists as Leonard, 
Traas. and Marcel de Serres; the latter suggests 
that the name of " hiimatilia' " l)e used instead of 
fossils for petrifactions of tlie latter kind. This 
strict distinction between the primeval and pres- 
ent world is connecteil with the theorj' tliat the 
plants and animals which are supposed to belong 
to the earlier periods of the earth's history all 
became extinct, and that after a tabula rasa, as it 
were, had thus been made upon the earth, the 
present vegetable and animal world was created. 
Thus, fossil men would be primeval men ; so that, 
if it could be proved that these fossil mm exist, 
it would follow that in ancient times the earth 
was inhaliited by men — the ao-ctMfA pre-Adamites, 
who were not our ancestors, but a race that died 
out before our historic ancestors appeared upon 
the world's stage. Most of our modem geologists 
have given up the idea of a strict distinction, in 
the sense we have spoken of, between the present 
and primeval world, .\ccording to the theory 
which is gradually becoming established, some 
kinds of animals which exist now also existed in 
the earlier periods ; and we are therefore not justi- 
fied in assuming that a geological catastrophe took 
place, which destroyed the former animal and veg- 
etable world which preceded the present fauna 
and flora. Consequently, there is no distinct 
boundary between the primeval and present 
world, in the sense spoken of, and the idea of a 
primeval race of men falls to the ground. If the 
period before the appearance of man on earth is 
called the primeval age, of course there can be no 
question of primeval men ; they w ould have ex- 
isted before all the records we luive of the first 
man. However, there is much yet shrouded in 
mystery regarding the development of man in 
pre-historic times, and there is much yet to learn 
and discover of a higher development and perfec- 
tion in planetary spheres. 
As the animals and plants whose remains are 
found in the strata of the separate systems must 
have lived on the earth before tliese sti-ata were 
formed, we can obtain a proximate idea of the 
fauna and fiora which belonged to the fossils that 
are found in the separate strata; for, on the one 
hand, those fossils which have been preserved are 
not thoroughly known; and, on the other hand, 
many organisms that may have existed were either 
not of a kind to be petrified, — such as fungas, 
slugs, etc., that are entirely wanting in hardness, 
— or could not be petrified because they existed 
on land", on high mountains, or in the air. Many 
geologists have overlo<iked these facts, and have 
hastily set up systems of the history of organic 
beings which later (ljscov(n-ies have shown to be 
false. It was formerly thought certain that land 
animals and lanjl plants had first appeared in the 
Carbon'iferous period; since then they have been 
found in the Devonian, or upp(!r Silurian system. 
Before 1824 many persons believed that reptiles 
first existed in tlie Permian period ; in the course 
of a decade it was proved that they had existed in 
the Carboniferous Age, and even liefore that time. 
Prior to 1818 everyone had accepted the general 
opinion that the earliest remains of warm-blooded 
animals occurred in the strata of the Cainozoic 
period; since then they have been found in the 
.Jin-assic, and even in the Triassic systems,— that 
is to say, in the Mesozoic system. It is because 
of tliis that Lyell asserts this conviction : that in 
some ways science is only on tlii! thresliold of 
discovery as to the order in whicli the separate 
classes of organisms appear in the strata, and that 
in the second half of the century, as in the first, it 
will repeatedly timl itself compelled to modify its 
previous theories. 
Petrified Plants in the Coal Measur<-s.—'Slost of 
the plants which are found petrified in the coal 
measures are land plants, especially tree-like 
ferns, and trees which existed between these and 
the pines. These plants seem to have been partly 
torn from the then existing forests by floods, and 
to have been collected together at the bottom of 
lakes, rivers, seas, or in narrow gulfs, and there 
transformed to coal. Probably most of the coal 
beds were fonned on the place where the trees and 
plants had grown. The vegetation passed first 
into the condition of peat moss ; was then fiooded 
by the sea, in consequence of the sinking of the 
land: was covered witli a layer of mud and sand; 
by a subsequent elevation, the mud was converted 
into dry land, and was fitted to produce a new 
