Mineral Point tribune. (Mineral Point, Wis.) 1869-1938, 1882-09-21
Fishes of the early Geological
PERIOD"

Editors TrtJu,e.-In our last es-
say we gave some remarkable ex-
amples of "fossil-shell crustacea,"
belonging to genera, which becam"
extinct after the deposit of the oldest
secondary strata. In the open seas
we pictured to ourselves the large
cephatopodas molluseS reigning par
amount, the tyrants Of creation;
enabled by their rapidity of move.
ment to chase their prey at the sur.
face, and by their curious hydraulic
contrivance to pursue it to the depths
of the ocean; and by their numerous
arms ana great strength, to conquer
and bring it within the grasp of
their powerful jaws. AS stated :,
these animals ceased to exist about
the commencement of the Tertiary
Age; d the next age, the Old Red
Sandstone, gives us notice of tire
mendous volcanic disturbances,
which broke up many rocks, and
perhaps had fatal effects upon many
of the previously existing species,
which then disappeared, and are no
more to be seen. In the course,
however, of this age, fishes which
had begun to appear in the proceed
ing period, become abundant. The
fish Of these earl y ayes, and of the
subsequent periods down to the
Chalk Era, have been divided into
two orders-but are not of the char
acter which now predomlnate-to
which names have been given, bear
ing reference to their external cover
ing, this being always a guide to the
general character of fishes. One
extensive order, RucoiljaHS, are so
called from the Greek word, p1dr,
y broad plate, being covered with
plates. The Sharks, Rays, and other
cartilaginoas fishes of the present
seas are living representatives of
this order. The other order is called
GaHOiliuiS from the Greek, gdROS,
meaning splendor, because of the
brilliancy Of the regularly arranged
angular scales, composed of bone
within, and enamel without, by
which the animals were covered.
OF this order, once SO extensive, we
have now no representatives, except
the Sturgeon and the bony pike of
the North Ameri can lakes.
The extinction of species is so
important n fact in Geology, and in
all that relates to the geological
history of the Earth, that we will, AT
the risk of being thought prohse,
try, 10y little popu ar explanation,
to make clear what is meant by The
term Each particular kind or genus
of animal usually consists of several
individuals, " hich, while they possess
Il common character or class of char.
acterS, have particular forms, which
Distinguish them from each other;
and such individuals constitute a
species of genus. The characters
by which biologists distinguish the
relative ages of strata, in so far rs
animal remains are concerned, de
pend not upon genus, but on the
species, for which species have be
come extinct, one after the other IN
succession the geHcra to which they
belong have continued to exist from
the period of the deposition Of the
oldest secondary strata to the present
time. For example, the gea,ts ostrea
or oyster, which are met with in
the lime stones that lie beneath the
coal.measurcs; but not one of the
many species of oyster, which are
found IN almost all the strata from
that limestone up to the chalk, is
identical with any species of oyster
inhabiting onr present seas.
One Of the families Of the Ga
nodians, the Sauroides, from their
structure make the nearest approach
to the next higher class of animal,
that follow, the Reptiles. Que Curl
Gus pecuharity has been remarked
in the tails Of both Placoids and
Ganoids. In that organ the
yertebral column is continued to the
extremity, and the tail may be said
to be fin extending from it down
wards, as seen in the existing shark
and dog-fsh. This is called the
heterocercal, or one-sided tail The
Placoid and CANDID fishes alone
reigned down TO the Chalk age.