life is dawn on the earth 22

life is dawn on the earth 22

"In the large quarry of Steinhag, from which I first obtained the

Eozoon, the enclosing rock is a grey hornblendic gneiss, which

sometimes passes into a hornblende-slate. The limestone is in many

places overlaid by a bed of hornblende-schist, sometimes five feet

in thickness, which separates it from the normal gneiss. In many

localities, a bed of serpentine, three or four feet thick, is

interposed between the limestone and the hornblende-schist; and in

some cases a zone, consisting chiefly of scapolite, crystalline and

almost compact, with an admixture however of hornblende and chlorite.

Below the serpentine band, the crystalline limestone appears divided

into distinct beds, and encloses various accidental minerals, among

which are reddish-white mica, chlorite, hornblende, tremolite,

chondrodite, rosellan, garnet, and scapolite, arranged in bands.

In several places the lime is mingled with serpentine, grains or

portions of which, often of the size of peas, are scattered through

the limestone with apparent irregularity, giving rise to a beautiful

variety of ophicalcite or serpentine-marble. These portions, which are

enclosed in the limestone destitute of serpentine, always present a

rounded outline. In one instance there appears, in a high naked wall

of limestone without serpentine, the outline of a mass of ophicalcite,

about sixteen feet long and twenty-five feet high, which, rising from

a broad base, ends in a point, and is separated from the enclosing

limestone by an undulating but clearly defined margin, as already well

described by Wineberger. This mass of ophicalcite recalls vividly a

reef-like structure. Within this and similar masses of ophicalcite in

the crystalline limestone, there are, so far as my observations in 1854

extend, no continuous lines or concentric layers of serpentine to be

observed, this mineral being always distributed in small grains and

patches. The few apparently regular layers which may be observed are

soon interrupted, and the whole aggregation is irregular."

 

It will be observed that this acervuline Eozoon of Steinhag appears to

exist in large reefs, and that in its want of lamination it differs

from the Canadian examples. In fossils of low organization, like

Foraminifera, such differences are often accidental and compatible with

specific unity, but yet there may be a difference specifically in the

Bavarian Eozoon as compared with the Canadian.

 

Gümbel also found in the Finnish and Bavarian limestones knotted

chambers, like those of Wentworth above mentioned (fig. 36), which he

regards as belonging to some other organism than Eozoon; and flocculi

having tubes, pores, and reticulations which would seem to point to the

presence of structures akin to sponges or possibly remains of seaweeds.

These observations Gümbel has extended into other localities in Bavaria

and Bohemia, and also in Silesia and Sweden, establishing the existence

of Eozoon fossils in all the Laurentian limestones of the middle and

north of Europe.

 

[Illustration: Fig. 36. _Archæospherinæ from Pargas in Finland._

(_After Gümbel._)

 

Magnified.]

 

Gümbel has further found in beds overlying the older Eozoic series,

and probably of the same age with the Canadian Huronian, a different

species of Eozoon, with smaller and more contracted chambers, and

still finer and more crowded canals. This, which is to be regarded as

a distinct species, or at least a well-marked varietal form, he has

named _Eozoon Bavaricum_ (fig. 37). Thus this early introduction of

life is not peculiar to that old continent which we sometimes call the

New World, but applies to Europe as well, and Europe has furnished a

successor to Eozoon in the later Eozoic or Huronian period. In rocks of

this age in America, after long search and much slicing of limestones,

I have hitherto failed to find any decided organic remains other than

the Tudor and Madoc specimens of Eozoon. If these are really Huronian

and not Laurentian, the Eozoon from this horizon does not sensibly

differ from that of the Lower Laurentian. The curious limpet-like

objects from Newfoundland, discovered by Murray, and described by

Billings,[AH] under the name _Aspidella_, are believed to be Huronian,

but they have no connection with Eozoon, and therefore need not detain

us here.

 

[Footnote AH: _Canadian Naturalist_, 1871.]

 

[Illustration: Fig. 37. _Section of Eozoon Bavaricum, with Serpentine,

from the Crystalline Limestone of the Hercynian primitive Clay-state

Formation at Hohenberg; 25 diameters._

 

(_a._) Sparry carbonate of lime. (_b._) Cellular carbonate of lime.

(_c._) System of tubuli. (_d._) Serpentine replacing the coarser

ordinary variety. (_e._) Serpentine and hornblende replacing the finer

variety, in the very much contorted portions.]

 

Leaving the Eozoic age, we find ourselves next in the Primordial or

Cambrian, and here we discover the sea already tenanted by many

kinds of crustaceans and shell-fishes, which have been collected and

described by palæontologists in Bohemia, Scandinavia, Wales, and North

America;[AI] curiously enough, however, the rocks of this age are

not so rich in Foraminifera as those of some succeeding periods. Had

this primitive type played out its part in the Eozoic and exhausted

its energies, and did it remain in abeyance in the Primordial age to

resume its activity in the succeeding times? It is not necessary to

believe this. The geologist is familiar with the fact, that in one

formation he may have before him chiefly oceanic and deep-sea deposits,

and in another those of the shallower waters, and that alternations

of these may, in the same age or immediately succeeding ages, present

very different groups of fossils. Now the rocks and fossils of the

Laurentian seem to be oceanic in character, while the Huronian and

early Primordial rocks evidence great disturbances, and much coarse

and muddy sediment, such as that found in shallows or near the land.

They abound in coarse conglomerates, sandstones and thick beds of slate

or shale, but are not rich in limestones, which do not in the parts

of the world yet explored regain their importance till the succeeding

Siluro-Cambrian age. No doubt there were, in the Primordial, deep-sea

areas swarming with Foraminifera, the successors of Eozoon; but these

are as yet unknown or little known, and our known Primordial fauna is

chiefly that of the shallows. Enlarged knowledge may thus bridge over

much of the apparent gap in the life of these two great periods.

 

[Footnote AI: Barrande, Angelin, Hicks, Hall, Billings, etc.]

 

Only as yet on the coast of Labrador and neighbouring parts of North

America, and in rocks that were formed in seas that washed the old

Laurentian rocks, in which Eozoon was already as fully sealed up as

it is at this moment, do we find Protozoa which can claim any near

kinship to the proto-foraminifer. These are the fossils of the genus

_Archæocyathus_--"ancient cup-sponges, or cup-foraminifers," which

have been described in much detail by Mr. Billings in the reports of

the Canadian Survey. Mr. Billings regards them as possibly sponges,

or as intermediate between these and Foraminifera, and the silicious

spicules found in some of them justify this view, unless indeed, as

partly suspected by Mr. Billings, these belong to true sponges which

may have grown along with Archæocyathus or attached to it. Certain

it is, however, that if allied to sponges, they are allied also to

Foraminifera, and that some of them deviate altogether from the sponge

type and become calcareous chambered bodies, the animals of which can

have differed very little from those of the Laurentian Eozoon. It is

to these calcareous Foraminiferal species that I shall at present

restrict my attention. I give a few figures, for which I am indebted to

Mr. Billings, of three of his species (figs. 38 to 40), with enlarged

drawings of the structures of one of them which has the most decidedly

foraminiferal characters.

 

[Illustration: Fig. 38. _Archæocyathus Minganensis--a Primordial

Protozoon._ (_After Billings._)

 

(_a._) Pores of the inner wall.]

 

[Illustration: Fig. 39. _Archæocyathus profundus--showing the base of

attachment and radiating chambers._ (_After Billings._)]

 

[Illustration: Fig. 40. _Archæocyathus Atlanticus--showing outer

surface and longitudinal and transverse sections._ (_After Billings._)]

 

[Illustration: Fig. 41. _Structures of Archæocyathus Profundus._

 

(_a._) Lower acervuline portion. (_b._) Upper portion, with three of

the radiating laminæ. (_c._) Portion of lamina with pores and thickened

part with canals. In figs. _a_ and _b_ the calcareous part is unshaded.]

 

To understand Archæocyathus, let us imagine an inverted cone of

carbonate of lime from an inch or two to a foot in length, and with

its point buried in the mud at the bottom of the sea, while its open

cup extends upward into the water. The lower part buried in the soil

is composed of an irregular acervuline network of thick calcareous

plates, enclosing chambers communicating with one another (figs. 40

and 41 A). Above this where the cup expands, its walls are composed

of thin outer and inner plates, perforated with innumerable holes,

and connected with each other by vertical plates, which are also

perforated with round pores, establishing a communication between the

radiating chambers into which they divide the thickness of the wall

(figs. 38, 39, and 41 B). In such a structure the chambers in the wall

of the cup and the irregular chambers of the base would be filled with

gelatinous animal matter, and the pseudopods would project from the

numerous pores in the inner and outer wall. In the older parts of the

skeleton, the structure is further complicated by the formation of

thin transverse plates, irregular in distribution, and where greater

strength is required a calcareous thickening is added, which in some

places shows a canal system like that of Eozoon (fig. 41, B, C).[AJ]

As compared with Eozoon, the fossils want its fine perforated wall,

but have a more regular plan of growth. There are fragments in the

Eozoon limestones which may have belonged to structures like these;

and when we know more of the deep sea of the Primordial, we may

recover true species of Eozoon from it, or may find forms intermediate

between it and Archæocyathus. In the meantime I know no nearer bond of

connection between Eozoon and the Primordial age than that furnished

by the ancient cup Zoophytes of Labrador, though I have searched very

carefully in the fossiliferous conglomerates of Cambrian age on the

Lower St. Lawrence, which contain rocks of all the formations from the

Laurentian upwards, often with characteristic fossils. I have also made

sections of many of the fossiliferous pebbles in these conglomerates

without finding any certain remains of such organisms, though the

fragments of the crusts of some of the Primordial tribolites, when

their tubuli are infiltrated with dark carbonaceous matter, are so like

the supplemental skeleton of Eozoon, that but for their forms they

might readily be mistaken for it; and associated with them are broken

pieces of other porous organisms which may belong to Protozoa, though