The Indiana State sentinel. [volume] (Indianapolis) 1868-1895, 1884-11-26
THE GEOLOGICAL GENESIS OF TIE
HORSE.

While physicists and dynamioal biologists
are discussing the question regarding a huid
or solid center OF the earth sud presenting
an array of physical and mathematical evil
dence pro and con, the more humble work
ers IN the geological field content themselves
with the study OF SO much OF the esrth's
crust as has been exposed to view by the cy
cles OF changes to which this outsr intsgu-
ment of the globe has been subjected. The
geologist has been able to study thickness
amounting to twenty miles or more OF this
rocky crust, aud the history which it reveals
is as marvellous as the workings OF Mephis-
tophelss or the imagination OF a Jules
Verne.
For the purpose of study aad clelrness Of
expression this crust has been sabdivited
into q number OF parts that are recognizable
by the character of organic remains that are
found entombed and known as fossils 1t is
not possible to point out with certainty
the primitive rocks from which the sedimen-
taIy rocks that form the greater part OF this
column were derived. nor the length OF time,
measured by years, which it required to &C
cumulate such body OF material as mud
as the bottom of ancient oceans But he is
enabled to give relative times from the fact
that the bottom rocks were formed first, aud
these were followed by newer aud newer de-
posts ur til We reach the top of the column
and arrive at the historic period.
The bottom sedimeutsry rocks are not only
the Oldest in time, bat they likewise contain
the remains OF older forms of life, aud We
find succession OF changes from the earlier
life on the globe until we have the advent OF
man
Among the most interesting revelations
reached, and one that adds aim 1st incoatro-
vertible evidence in favor OF the doctrine of
evolution, is the changes that have taken
place in the genesis OF the horse, as shown
bytHuxley and Marsh and Cope.
In the lower beds OF the Tertiary period,
known as the EOcene epoch. are found the
remains of the earliest known animal refera.
bic to the horse family. This animal had
three toes on the hind foot and four service
able toes on the fore foot, and an imperfect
9Th, that answers to the thumb. The two
bones of the leg and fore arm are entirely
distinct, and the animal was no larger than
fox. In the middle part OF this E9ceae
came the OrohiPpus (of Marsh, an
animal OF similar size and structure,
except that the rUdimentsry thumb,
| or dew-claw, is ropped, leaving
| only four toes on the fore foot. Next in
time is found in the LOrer WiOocne, the MesO.
hippus, in which the fourth toe has become
rudimentary and a useless splint. Still in
the MiOceae came the Miohippus, in which
the rudimentary spliut is almost gone and
the middle hcof has become larger, yet the
| two side hoofs are still seryicesble. The two
| bones have also become united though stIll
quite distinct. The animal was about the
size of sheep. In the Upper Moeeas, and
Lo,ser PIioeeae is found tbs Pr0to
| hippas OF this country, which is allied
| to the HppariOa of Europe, an animal still
more horse like than the preceding. both 10
structure and size. In this animal every
| remnant of the fourth sp,int is gone, the
hoof has become still larger, and the two
! inside hoofs smaller and shorter and no
longer serviceable, except in mushy ground
| It was about the size of the ass. Now in the
Phocene is found. the Pliohippus, almost COM
| plete horse. The hoofs are reduced to one,
but the splints of the two side toes remain to
| bear witHess to the line of des.
cent. It differs from the true horse in
| the skull, shape OF the hoois, the
| moIars and some other less important de-
tails. Last comes the EqluIs in the Qtatera.
| arr age, so closely resembling the living
horse that they are placed ir the same genus
and species. The hoof becomes rounder, the
| splint-boRes shorter, the molars longer, the
second bone OF the leg more rudinlentsry,
and the evolutionary change from lower
to the highest form of horse is by geological
evidence made complete. In order to make
the occurrence Of these animals in geological
time better understood by the general reader,
the following order represents the various
epochs in decending order:
| Quaternary period: Age of man.
Tertiary: Pliocine, Miocine, Eocine.
Beside the horse family in the geological
ages noted above, there has been found a
multitude OF singular animal which 1t Is
not necessary to enumerate in this article,
which we will close by quotation from
Cope and Wortmanss report on the Quarter
nary Vertebrstes, to be published in the
] State Biologists forthcoming yolume-No.
Fourteen: