life is dawn on the earth 19

life is dawn on the earth 19

The following on this subject is from a memoir by Dr. Hunt in the

_Twenty-first Report of the Regents of the University of New York_,

1874:--

 

"Recent investigations have shown that in some cases the

dissemination of certain of these minerals through the crystalline

limestones is connected with organic forms. The observations

of Dr. Dawson and myself on the Eozoon Canadense showed that

certain silicates, namely serpentine, pyroxene, and loganite,

had been deposited in the cells and chambers left vacant by the

disappearance of the animal matter from the calcareous skeleton of

the foraminiferous organism; so that when this calcareous portion is

removed by an acid there remains a coherent mass, which is a cast of

the soft parts of the animal, in which, not only the chambers and

connecting canals, but the minute tubuli and pores are represented

by solid mineral silicates. It was shown that this process must have

taken place immediately after the death of the animal, and must have

depended on the deposition of these silicates from the waters of the

ocean.

 

"The train of investigation thus opened up, has been pursued by

Dr. Gümbel, Director of the Geological Survey of Bavaria, who, in

a recent remarkable memoir presented to the Royal Society of that

country, has detailed his results.

 

"Having first detected a fossil identical with the Canadian Eozoon

(together with several other curious microscopic organic forms not

yet observed in Canada), replaced by serpentine in a crystalline

limestone from the primitive group of Bavaria, which he identified

with the Laurentian system of this country, he next discovered a

related organism, to which he has given the name of Eozoon Bavaricum.

This occurs in a crystalline limestone belonging to a series of rocks

more recent than the Laurentian, but older than the Primordial zone

of the Lower Silurian, and designated by him the Hercynian clay slate

series, which he conceives may represent the Cambrian system of Great

Britain, and perhaps correspond to the Huronian series of Canada and

the United States. The cast of the soft parts of this new fossil is,

according to Gümbel, in part of serpentine, and in part of hornblende.

 

"His attention was next directed to the green hornblende (pargasite)

which occurs in the crystalline limestone of Pargas in Finland, and

remains when the carbonate of lime is dissolved as a coherent mass

closely resembling that left by the irregular and acervuline forms

of Eozoon. The calcite walls also sometimes show casts of tubuli....

A white mineral, probably scapolite was found to constitute some

tubercles associated with the pargasite, and the two mineral species

were in some cases united in the same rounded grain.

 

"Similar observations were made by him upon specimens of coccolite

or green pyroxene, occurring in rounded and wrinkled grains in a

Laurentian limestone from New York. These, according to Gümbel,

present the same connecting cylinders and branching stems as the

pargasite, and are by him supposed to have been moulded in the

same manner.... Very beautiful evidences of the same organic

structure consisting of the casts of tubuli and their ramifications,

were also observed by Gümbel in a purely crystalline limestone,

enclosing granules of chondrodite, hornblende, and garnet, from

Boden in Saxony. Other specimens of limestone, both with and without

serpentine and chondrodite, were examined without exhibiting any

traces of these peculiar forms; and these negative results are

justly deemed by Gümbel as going to prove that the structure of

the others is really, like that of Eozoon, the result of the

intervention of organic forms. Besides the minerals observed in the

replacing substance of Eozoon in Canada, viz., serpentine, pyroxene,

and loganite, Gümbel adds chondrodite, hornblende, scapolite, and

probably also pyrallolite, quartz, iolite, and dichroite."

 

 

(D.) Glauconites.

 

The following is from a paper by Dr. Hunt in the _Report of the

Survey of Canada_ for 1866:--

 

"In connection with the Eozoon it is interesting to examine more

carefully into the nature of the matters which have been called

glauconite or green-sand. These names have been given to substances

of unlike composition, which, however, occur under similar

conditions, and appear to be chemical deposits from water, filling

cavities in minute fossils, or forming grains in sedimentary rocks

of various ages. Although greenish in colour, and soft and earthy

in texture, it will be seen that the various glauconites differ

widely in composition. The variety best known, and commonly regarded

as the type of the glauconites, is that found in the green-sand of

Cretaceous age in New Jersey, and in the Tertiary of Alabama; the

glauconite from the Lower Silurian rocks of the Upper Mississippi is

identical with it in composition. Analysis shows these glauconites to

be essentially hydrous silicates of protoxyd of iron, with more or

less alumina, and small but variable quantities of magnesia, besides

a notable amount of potash. This alkali is, however, sometimes

wanting, as appears from the analysis of a green-sand from Kent in

England, by that careful chemist, the late Dr. Edward Turner, and

in another examined by Berthier, from the _calcaire grossier_, near

Paris, which is essentially a serpentine in composition, being a

hydrous silicate of magnesia and protoxyd of iron. A comparison of

these last two will show that the loganite, which fills the ancient

Foraminifer of Burgess, is a silicate nearly related in composition.

 

I. Green-sand from the _calcaire grossier_, near Paris. Berthier

(cited by Beudant, _Mineralogie_, ii., 178).

 

II. Green-sand from Kent, England. Dr. Edward Turner (cited by

Rogers, Final Report, Geol. N. Jersey, page 206).

 

III. Loganite from the Eozoon of Burgess.

 

IV. Green-sand, Lower Silurian; Red Bird, Minnesota.

 

V. Green-sand, Cretaceous, New Jersey.

 

VI. Green-sand, Lower Silurian, Orleans Island.

 

The last four analyses are by myself.

 

I. II. III. IV. V. VI.

 

Silica 40·0 48·5 35·14 46·58 50·70 50·7

 

Protoxyd of iron 24·7 22·0 8·60 20·61 22·50 8·6

 

Magnesia 16·6 3·8 31·47 1·27 2·16 3·7

 

Lime 3·3 .... .... 2·49 1·11 ....

 

Alumina 1·7 17·0 10·15 11·45 8·03 19·8

 

Potash .... traces. .... 6·96 5·80 8·2

 

Soda .... .... .... ·98 ·75 ·5

 

Water 12·6 7·0 14·64 9·66 8·95 8·5

---- ---- ------ ------ ------ -----

98·9 98·3 100·00 100·00 100·00 100·0"

 

[Illustration:

Plate VI.

 

From a Photo. by Weston. Vincent Brooks, Day & Son Lith.

 

CANAL SYSTEM OF EOZOON.

 

SLICES OF THE FOSSIL (MAGNIFIED.)

 

_To face Chap. 6._]

 

 

 

 

CHAPTER VI.

 

CONTEMPORARIES AND SUCCESSORS OF EOZOON.

 

 

The name Eozoon, or Dawn-animal, raises the question whether we shall

ever know any earlier representative of animal life. Here I think

it necessary to explain that in suggesting the name Eozoon for the

earliest fossil, and Eozoic for the formation in which it is contained,

I had no intention to affirm that there may not have been precursors

of the Dawn-animal. By the similar term, Eocene, Lyell did not mean

to affirm that there may not have been modern types in the preceding

geological periods: and so the dawn of animal life may have had its

gray or rosy breaking at a time long anterior to that in which Eozoon

built its marble reefs. When the fossils of this early auroral time

shall be found, it will not be hard to invent appropriate names for

them. There are, however, two reasons that give propriety to the

name in the present state of our knowledge. One is, that the Lower

Laurentian rocks are absolutely the oldest that have yet come under

the notice of geologists, and at the present moment it seems extremely

improbable that any older sediments exist, at least in a condition to

be recognised as such. The other is that Eozoon, as a member of the

group Protozoa, of gigantic size and comprehensive type, and oceanic in

its habitat, is as likely as any other creature that can be imagined

to have been the first representative of animal life on our planet.