life is dawn on the earth 14

life is dawn on the earth 14

"The successive layers, each having its own proper wall, are

often superposed one upon another without the intervention of any

supplemental or intermediate skeleton such as presents itself in

all the more massive forms of the Nummuline series; but a deposit

of this form of shell-substance, readily distinguishable by its

homogeneousness from the finely tubular shell immediately investing

the segments of the sarcode-body, is the source of the great

thickening which the calcareous zones often present in vertical

sections of Eozoon. The presence of this intermediate skeleton has

been correctly indicated by Dr. Dawson; but he does not seem to have

clearly differentiated it from the proper wall of the chambers.

All the tubuli which he has described belong to that canal system

which, as I have shown,[T] is limited in its distribution to the

intermediate skeleton, and is expressly designed to supply a channel

for its nutrition and augmentation. Of this canal system, which

presents most remarkable varieties in dimensions and distribution, we

learn more from the casts presented by decalcified specimens, than

from sections, which only exhibit such parts of it as their plane may

happen to traverse. Illustrations from both sources, giving a more

complete representation of it than Dr. Dawson's figures afford, have

been prepared from the additional specimens placed in my hands.

 

[Footnote T: _Op. cit._, pp. 50, 51.]

 

"It does not appear to me that the canal system takes its origin

directly from the cavity of the chambers. On the contrary, I believe

that, as in Calcarina (which Dr. Dawson has correctly referred to as

presenting the nearest parallel to it among recent Foraminifera),

they originate in lacunar spaces on the outside of the proper

walls of the chambers, into which the tubuli of those walls open

externally; and that the extensions of the sarcode-body which

occupied them were formed by the coalescence of the pseudopodia

issuing from those tubuli.[U]

 

[Footnote U: _Op. cit._, p. 221.]

 

"It seems to me worthy of special notice, that the canal system,

wherever displayed in transparent sections, is distinguished by a

yellowish brown coloration, so exactly resembling that which I have

observed in the canal system of recent Foraminifera (as Polystomella

and Calcarina) in which there were remains of the sarcode-body, that

I cannot but believe the infiltrating mineral to have been dyed by

the remains of sarcode still existing in the canals of Eozoon at the

time of its consolidation. If this be the case, the preservation

of this colour seems to indicate that no considerable metamorphic

action has been exerted upon the rock in which this fossil occurs.

And I should draw the same inference from the fact that the organic

structure of the shell is in many instances even more completely

preserved than it usually is in the Nummulites and other Foraminifera

of the Nummulitic limestone of the early Tertiaries.

 

"To sum up,--That the _Eozoon_ finds its proper place in the

Foraminiferal series, I conceive to be conclusively proved by its

accordance with the great types of that series, in all the essential

characters of organization;--namely, the structure of the shell

forming the proper wall of the chambers, in which it agrees precisely

with Nummulina and its allies; the presence of an intermediate

skeleton and an elaborate canal system, the disposition of which

reminds us most of Calcarina; a mode of communication of the chambers

when they are most completely separated, which has its exact parallel

in Cycloclypeus; and an ordinary want of completeness of separation

between the chambers, corresponding with that which is characteristic

of Carpenteria.

 

"There is no other group of the animal kingdom to which Eozoon

presents the slightest structural resemblance; and to the suggestion

that it may have been of kin to Nullipore, I can offer the most

distinct negative reply, having many years ago carefully studied the

structure of that stony Alga, with which that of Eozoon has nothing

whatever in common.

 

"The objections which not unnaturally occur to those familiar with

only the ordinary forms of Foraminifera, as to the admission of

Eozoon into the series, do not appear to me of any force. These have

reference in the first place to the great _size_ of the organism; and

in the second, to its exceptional mode of growth.

 

"1. It must be borne in mind that all the Foraminifera normally

increase by the continuous gemmation of new segments from those

previously formed; and that we have, in the existing types, the

greatest diversities in the extent to which this gemmation may

proceed. Thus in the Globigerinæ, whose shells cover to an unknown

thickness the sea bottom of all that portion of the Atlantic Ocean

which is traversed by the Gulf Stream, only eight or ten segments

are ordinarily produced by continuous gemmation; and if new segments

are developed from the last of these, they detach themselves so

as to lay the foundation of independent Globigerinæ. On the other

hand in Cycloclypeus, which is a discoidal structure attaining two

and a quarter inches in diameter, the number of segments formed by

continuous gemmation must be many thousand. Again, the Receptaculites

of the Canadian Silurian rocks, shown by Mr. Salter's drawings[V]

to be a gigantic Orbitolite, attains a diameter of twelve inches;

and if this were to increase by vertical as well as by horizontal

gemmation (after the manner of Tinoporus or Orbitoides) so that one

discoidal layer would be piled on another, it would form a mass

equalling Eozoon in its ordinary dimensions. To say, therefore, that

Eozoon cannot belong to the Foraminifera on account of its gigantic

size, is much as if a botanist who had only studied plants and

shrubs were to refuse to admit a tree into the same category. The

very same continuous gemmation which has produced an Eozoon would

produce an equal mass of independent Globigerinæ, if after eight

or ten repetitions of the process, the new segments were to detach

themselves.

 

[Footnote V: _First Decade of Canadian Fossils_, pl. x.]

 

"It is to be remembered, moreover, that the largest masses of sponges

are formed by continuous gemmation from an original Rhizopod segment;

and that there is no _à priori_ reason why a Foraminiferal organism

should not attain the same dimensions as a Poriferal one,--the

intimate relationship of the two groups, notwithstanding the

difference between their skeletons, being unquestionable.

 

"2. The difficulty arising from the zoophytic plan of growth of

Eozoon is at once disposed of by the fact that we have in the recent

Polytrema (as I have shown, _op. cit._, p. 235) an organism nearly

allied in all essential points of structure to Rotalia, yet no

less aberrant in its plan of growth, having been ranked by Lamarck

among the Millepores. And it appears to me that Eozoon takes its

place quite as naturally in the Nummuline series as Polytrema in

the Rotaline. As we are led from the typical Rotalia, through the

less regular Planorbulina, to Tinoporus, in which the chambers are

piled up vertically, as well as multiplied horizontally, and thence

pass by an easy gradation to Polytrema, in which all regularity of

external form is lost; so may we pass from the typical Operculina or

Nummulina, through Heterostegina and Cycloclypeus to Orbitoides, in

which, as in Tinoporus, the chambers multiply both by horizontal and

by vertical gemmation; and from Orbitoides to Eozoon the transition

is scarcely more abrupt than from Tinoporus to Polytrema.

 

"The general acceptance, by the most competent judges, of my views

respecting the primary value of the characters furnished by the

intimate structure of the shell, and the very subordinate value

of plan of growth, in the determination of the affinities of

Foraminifera, renders it unnecessary that I should dwell further on

my reasons for unhesitatingly affirming the Nummuline affinities of

Eozoon from the microscopic appearances presented by the proper wall

of its chambers, notwithstanding its very aberrant peculiarities;

and I cannot but feel it to be a feature of peculiar interest in

geological inquiry, that the true relations of by far the earliest

fossil yet known should be determinable by the comparison of a

portion which the smallest pin's head would cover, with organisms at

present existing."

 

 

(C.) Note on Specimens From Long Lake and Wentworth.

 

[_Journal of Geological Society_, August, 1867.]

 

"Specimens from Long Lake, in the collection of the Geological

Survey of Canada, exhibit white crystalline limestone with light

green compact or septariiform[W] serpentine, and much resemble some

of the serpentine limestones of Grenville. Under the microscope the

calcareous matter presents a delicate areolated appearance, without

lamination; but it is not an example of acervuline Eozoon, but rather

of fragments of such a structure, confusedly aggregated together, and

having the interstices and cell-cavities filled with serpentine. I

have not found in any of these fragments a canal system similar to

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