162 
POPULAR SCIEI^CE NEAVS. 
[November, 1S90. 
of self-protection. The bell-shaped corolla 
touched the earth lightly, but closely, and 
was cemented to the soil by the frozen moist- 
ure around its rim, thus enclosing the stamens 
and other important organs of the flowers in 
a temporary tent, as it were, and protecting 
them from the outside cold. This movement 
was repeated for four successive cold nights. 
On the fifth night the temperature moderated, 
and, although snow fell, the flower and stalk 
remained in their usual upright position ; and 
in due time the blossom withered and pro- 
duced seed as usual. 
These remarkable spontaneous movements 
of the plant seem to be almost allied to those 
of certain low forms of animal life, and are 
extremely difiicult to explain, as is also the 
remarkable resistance to low temperatures 
of many other early flowers, such as the 
snow-drop and crocus. We would suggest 
to the members of the Agassiz Association 
that this observation will be an excellent one 
to repeat the coming spring, especially as 
our climate is excelled by that of no other 
country in the production of sudden and 
marked changes of temperature, particularly 
in the early spring months. 
[Original in Popular Science News.'] 
GEOLOGICAL DEVELOPMENT— PETRIFAC- 
TIONS AND FOSSILS. 
BY JOSEPH WALLACE. 
In this article we reach the period of geological 
development which treats of petrifactions and fossils. 
The name petrifaction, as formerly in use, does not 
apply to those organic bodies which have been 
preserved entire with the original proportions 
of their elementary parts — such as insects and parts 
of plants which have been inclosed in amber or 
rock salt, and bodies of mammoths which have 
been dug out of Siberian ice in a preserved condi- 
tion. Generally the softer parts of the bodies 
of animals and plants which were inclosed in the 
hardening masses of the strata were dissolved, 
destroyed, or decayed, and, as a rule, only the 
firmer and harder parts of the organism have been 
well preserved. This is especially the case with 
stems, branches, hard fruits of plants, bones, teeth, 
shells, scales, and horns of animals. 
Many organic bodies, especially those of plants, 
have become carbonized and changed into peat and 
coal ; others, particularly the bodies of animals, 
have become lixiviated and disintegrated, that is, 
they have lost their gelatinous and other animal 
substances by gradual destruction and lixiviation. 
In this altered and calcine state, their color, hard- 
ness, and weiglit have more or less disappeared. 
Other organic bodies have been covered, surrounded, 
or encrusted, as it is technically called, with sub- 
stances, as, for instance, calcareous tufa, which were 
originally fluid and then hardened. But the real 
petrifaction occurs when an organic body is entirely 
changed into a mineral sujjstance and still retains 
its original form. The solid parts of an organic 
body are porous. The pores are filled up by the 
minerals, which are dissolved in water, and the 
substance of the organic body is by degrees chemi- 
cally removed ; the mineral substance replaces it 
and gradually hardens, so that at last the organic 
substances have made way for mineral substances 
without producing an important change in the 
original form. 
IchnoHtes. — Sometimes an organic body, after 
being entirely dissolved and washed away, has left 
the impression of its outward form on the surround- 
ing mineral rocks; stems of trees, for instance, 
inclosed in some rock, having decayed in this man- 
ner, and their component parts entirely carried 
away, in their place hollow spots have been left, 
which have been filled up by some mineral sub- 
stance, and this has taken the form of the original 
tree. 
Huxley, in liis work, On Our Knowledge of the 
Causes of Phenomena of Organic Nature, p. 45, cites 
an instance which came under his observation : 
"Some years ago I had to make inquiry into tlie 
nature of some very curious fossils sent to me from 
the North of Scotland— a series of holes in some 
pieces of rock, and nothing more. These holes, 
however, had a certain definite shape about them ; 
and when I got a skilful workman to make castings 
of the interior of these holes, I found that they were 
the impressions of the joints of a back-bone, and 
of the armor of a great reptile, twelve or more feet 
long. This great beast had died and got buried in 
the sand ; the sand had gradually hardened over the 
bones, but remained porous. Water had trickled 
through it, and that water being probably charged 
with a superfluity of carbonic acid, had dissolved all 
the phosphate and carbonate of lime, and the bones 
■themselves had thus decayed and entirely dis- 
appeared ; but, as the sandstone liappened to have 
consolidated by that time, the precise shape of the 
bones was retained." 
The fossil footprints, or ichnolites, belong to this 
class. These are impressions originally made by 
animals in clay or sand, and preserved in the shale 
or sandstone rock resulting from the solidification 
of thoee materials. Under these names have been 
included markings of various forms in rocks of very 
different geological ages. The fossil footprints were 
first observed by a Scotch gentleman. Dr. Duncan, 
and since then they have been frequently found. 
The animal to which these footprints have been 
ascribed has been named Cheirotherium, or hand 
animal, because the impressions were really made 
by animals and did not originate in any other way. 
They have been found, too, in rows, one behind the 
other, so that the size of the step can be ascertained ; 
and in four-footed animals, the print of the hind 
feet can be distinguished from that of the fore 
feet. 
Another class of such impressions, called fossil 
rain-drops, do not seem to be authentic. Small, 
rounded impressions are sometimes found in 
sandstone strata and overlying stratum, and 
corresponding rounded formations in relief. It 
was once thought these impressions were pro- 
duced by falling rain-drops, that is, from rain 
which fell in primitive times when the sandstone 
was beginning to harden. In one case it was 
thought the direction from which the rain came 
could be discovered, because the sides of the 
impressions are rather elevated on one side, just 
as would be the case if rain was driven sideways 
and fell on one of our sandy shores. But Vogt 
says: "The impressions have been recently 
much more explained by the action of the atmos- 
phere on the cement of the sandstone, or by 
air bubbles left on the surface of the sand, which 
was covered with the waves. This superficial change 
takes place sooner or later in most sandstones, 
according to the quality of tlie cement." 
Fossils. — From very remote times men had ob- 
served these objects in the rocky strata far above the 
level of the ocean. Pythagoras, Plato, Aristotle, 
Strabo, Seneca, and Pliny allude to the existence 
of marine shells at a long distance from the sea. 
All the ancients attributed their occurrence to 
changes of the earth's surface, and considered them 
conclusive evidence of the rocks containing them 
having been submerged beneath the ocean. 
In the beginning of the sixteenth century, when 
the learned of Europe turned their attention to 
geological phenomena, fanciful opinions were pro- 
mulgated, attributing these forms to lusus naturte, — 
"sports of nature," — the plastic force of nature 
which effected these resemblances ; or that, dating 
from the first creation, they were produced at the 
time of the formation of crystals or the mountains 
themselves. More than a century was necessary to 
disprove this theory, and an additional century and 
a half to explode the hypothesis that organized 
bodies had all been buried in the solid strata by our 
historic Flood. During the time in question, how- 
ever, there was not wanting those who maintained 
more rational opinions. In the early part of the 
sixteenth century, Leonardo da Vinci, having 
planned and superintended some canals in the 
North of Italy, opposed these views, asserting that 
the mud of rivers flowing into the sea had carried 
and penetrated into the interior of the shells when 
they were still beneath the water. Soon after this, 
Fracastora, on the occasion of some excavations 
made about the city of Verona, declared his opinion 
that fossil shells had all belonged to living animals, 
which existed and multiplied in the positions where 
the remains were now found. 
After it had been generally acknowledged that 
fossils were the remains of animals and plants 
which had formerly existed on the earth, the question 
arose as to how they had come to be inclosed in the 
strata. The Deluge was first thought of; the ani- 
mals had probably been killed in the floods, their 
remains and the plants had been inclosed in the 
deposits made by the waters, which deposits had 
subsequently hardened. This theory was supported 
in the last century by Drs. Woodward and J. J. 
Schleuchzer, the latter a Swiss physician, who pub- 
lished a large work with drawings, wherein he 
spiritedly defended the theory of fossils as being-the 
remains of the Flood. He even believed he had 
found a fossil man, which he called homo dilurii 
testis, that had perished in the Deluge. Through 
this the attention of the naturalists became more 
interesting and searching, and they began to make 
