less
number of stars measures the relative depth of the stratum in different
directions; giving in each case, like the marks on a sounding-line, the
comparative length of visual ray required to reach the bottom; or, more
properly, as above and below do not here apply, the outer limit of the
sidereal stratum.

In the direction of the major axis, where the greater number of stars
are placed behind each other, the remoter ones appear closely crowded
together, and, as it were, united by a milky radiance, and present a
zone or belt projected on the visible celestial vault. This narrow belt
is divided into branches; and its beautiful, but not uniform brightness,
is interrupted by some dark places. As seen by us on the apparent
concave celestial sphere, it deviates only a few degrees from a great
circle, we being near the middle of the entire starry cluster, and
almost in the plane of the Milky Way. If out planetary system were far
outside the cluster, the Milky Way would appear to telescopic vision as
a ring, and at a still greater distance as a resolvable disc-shaped
nebula.

_IV.--On Earth History_

The succession and relative age of different geological formations are
traced partly by the order of superposition of sedimentary strata, of
metamorphic beds, and of conglomerates, but most securely by the
presence of organic remains and their diversities of structure. In the
fossiliferous strata are inhumed the remains of the floras and faunas of
past ages. As we descend from stratum to stratum to study the relations
of superposition, we ascend in the order of time, and new worlds of
animal and vegetable existence present themselves to the view.

In our ignorance of the laws under which new organic forms appear from
time to time upon the surface of the globe, we employ the expression
"new creations" when we desire to refer to the historical phenomena of
the variations which have taken place at intervals in the animals and
plants that have inhabited the basins of the primitive seas and the
uplifted continents.

It has sometimes happened that extinct species have been preserved
entire, even to the minutest details of their tissues and articulations.
In the lower beds of the Secondary Period, the lias of Lyme Regis, a
sepia has been found so wonderfully preserved that a part of the black
fluid with which the animal was provided myriads of years ago to conceal
itself from its enemies has actually served at the present time