The Portland daily press. [volume] (Portland, Me.) 1862-1921, 1886-04-20
SOCIETY OF NATURAL HISTORY.
Lecture by Professor Lee of Rowdoin
College.

The speaker announced as his subject the
structure and mode of formation of lmestones.
Rocks composed largely of carbonate of lime are
called limestones. They may be conveniently
classified according to their mode of formation, as
chemical, mechanical or organic. Stalactites ,
travertne and calcareous sinter are examples of
the first group. These are all formed by the
precipitation of the lime from solution which
has been made by the percoation of carbo
water through limestone; and are usually found
In caves and around lime springs. The caoareous
shaleS in the West were referred to as giving
evidence of extensive mechanical erosion and re.
deposit OF limestone as soft mud which was after
wards consolidated and hardened retaining per-
organisms
Animals however, are the great limestone
stones even are primarily accumulated by ami
mails. Lime is everywhere found in solution
whether the water be fresh or salt. Animals take
it into their bodies in solution and use it to form
shells or bones. After death these are some
times left in beds extensive enough to form
rocks. Some of the lime is dissolved and serves
as a cement to hold the remaining portions to-
gether. The shell rock or "eoquina" of Florida
Is thus formed. Bone rock is exceed
ingly rare as vertebrateS are seldom found
in sufficient numbers together to allow of the ac-
emulation of a bed of bones. The lowest and
simplest animals produce the most extensive and
and chalk. The fossil coral beds OF Ohio and
Indiana are understood after studying the modern
reefs of the Pacific. Chalk is composed almost
entirely of the shells of Foraminifera. For long
time its origin was puzzing to geologists because
conditions suitable to the formation OF beds OF
such minute shells could nowhere be found, al
though similar shells were not uncommon among
the sands of every shore. Recent investigation OF
the deep sea has shown that, away from the ln-
fiuence of the Shore in depths not greater than
2500 fathoms there exists soft, sticky gray or
white mud composed almost wholly of the shells OF
Foraminifera, many species of which seem identi-
cal with those found in the chalk.
This mud is called "Globigerina ooze."
Samples of it were exhibited, including
some which under a pressure of 200 atmos-
phereS, in dry state had been consolidated into
q mass, having the conference and microscopieal
structure of chalk Without doubt the chalk cliffs
represent old sea bottom. There is a wonderful
similarity between the modern deep sea fauna
and that the remains of which exist in cretaceous
rocks. But that is not surprising when 1t IS con-
sidered that the conditions of life In the depths OF
the ocean cannot have materially changed since
cretaceouS times Any OF the varieties OF lime
stone may exhibit crystalline structure more or
less perfectly developed. This may be produced
in several ways Sometimes percolating waters
will rearrange the particles OF lime so that fine
crystals may be formed If strata of soft fossilif-
erous limestone are cut by trap dikes the parts ad
jacent to the trap will have all their fossils de-
stroyed and will be altered to a granular lime
stone or marble. Most granular lslestones and
marbles, however, have been made out of fossilif-
erous limestones by the ordinary processes of
metamorphism.