life is dawn on the earth 28

life is dawn on the earth 28

[Footnote AR: I may now refer in addition to the canals filled with

calcite and dolomite, detected by Dr. Carpenter and myself in specimens

from Petite Nation, and mentioned in a previous chapter. See also Plate

VIII.]

 

Further, the authors of the paper have no right to object to our

regarding the laminated specimen as "typical" Eozoon. If the question

were as to _typical ophite_ the case would be different; but the

question actually is as to certain well-defined forms which we regard

as fossils, and allege to have organic structure on the small scale,

as well as lamination on the large scale. We profess to account for

the acervuline forms by the irregular growth at the surface of the

organisms, and by the breaking of them into fragments confusedly

intermingled in great thicknesses of limestone, just as fragments of

corals occur in Palæozoic limestones; but we are under no obligation

to accept irregular or disintegrated specimens as typical; and when

objectors reason from these fragments, we have a right to point to

the more perfect examples. It would be easy to explain the loose

cells of _Tetradium_ which characterize the bird's-eye limestone

of the Lower Silurian of America, as crystalline structures; but

a comparison with the unbroken masses of the same coral, shows

their true nature. I have for some time made the minute structure

of Palæozoic limestones a special study, and have described some

of them from the Silurian formations of Canada.[AS] I possess now

many additional examples, showing fragments of various kinds of

fossils preserved in these limestones, and recognisable only by the

infiltration of their pores with different silicious minerals. It can

also be shown that in many cases the crystallization of the carbonate

of lime, both of the fossils themselves and of their matrix, has

not interfered with the perfection of the most minute of these

structures.

 

[Footnote AS: In the _Canadian Naturalist_.]

 

The fact that the chambers are usually filled with silicates is

strangely regarded by the authors as an argument against the organic

nature of Eozoon. One would think that the extreme frequency of

silicious fillings of the cavities of fossils, and even of silicious

replacement of their tissues, should have prevented the use of such

an argument, without taking into account the opposite conclusions to

be drawn from the various kinds of silicates found in the specimens,

and from the modern filling of Foraminifera by hydrous silicates, as

shown by Ehrenberg, Mantell, Carpenter, Bailey, and Pourtales.[AT]

Further, I have elsewhere shown that the loganite is proved by its

texture to have been a fragmental substance, or at least filled

with loose _debris_; that the Tudor specimens have the cavities

filled with a sedimentary limestone, and that several fragmental

specimens from Madoc are actually wholly calcareous. It is to be

observed, however, that the wholly calcareous specimens present

great difficulties to an observer; and I have no doubt that they are

usually overlooked by collectors in consequence of their not being

developed by weathering, or showing any obvious structure in fresh

fractures.

 

[Footnote AT: _Quarterly Journal Geol. Society_, 1864.]

 

3. With regard to the canal system, the authors persist in

confusing the casts of it which occur in serpentine with "metaxite"

concretions, and in likening them to dendritic crystallizations of

silver, etc., and coralloidal forms of carbonate of lime. In answer

to this, I think it quite sufficient to say that I fail to perceive

the resemblance as other than very imperfectly imitative. I may add,

that the case is one of the occurrence of a canal structure in forms

which on other grounds appear to be organic, while the concretionary

forms referred to are produced under diverse conditions, none of

them similar to those of which evidence appears in the specimens of

Eozoon. With the singular theory of pseudomorphism, by means of which

the authors now supplement their previous objections, I leave Dr.

Hunt to deal.

 

4. With respect to the proper wall and its minute tubulation, the

essential error of the authors consists in confounding it with

fibrous and acicular crystals, and in maintaining that because the

tubuli are sometimes apparently confused and confluent they must

be inorganic. With regard to the first of these positions, I may

repeat what I have stated in former papers--that the true cell-wall

presents minute cylindrical processes traversing carbonate of lime,

and usually nearly parallel to each other, and often slightly

bulbose at the extremity. Fibrous serpentine, on the other hand,

appears as angular crystals, closely packed together, while the

numerous spicular crystals of silicious minerals which often appear

in metamorphic limestones, and may be developed by decalcification,

appear as sharp angular needles usually radiating from centres or

irregularly disposed. Their own plate (Ophite from Skye, King and

Rowney's Paper, _Proc. R. I. A._, vol. x.), is an eminent example

of this; and whatever the nature of the crystals represented, they

have no appearance of being true tubuli of Eozoon. I have very often

shown microscopists and geologists the cell-wall along with veins of

chrysotile and coatings of acicular crystals occurring in the same or

similar limestones, and they have never failed at once to recognise

the difference, especially under high powers.

 

I do not deny that the tubulation is often imperfectly preserved,

and that in such cases the casts of the tubuli may appear to be

glued together by concretions of mineral matter, or to be broken

or imperfect. But this occurs in all fossils, and is familiar to

any microscopist examining them. How difficult is it in many cases

to detect the minute structure of Nummulites and other fossil

Foraminifera? How often does a specimen of fossil wood present in one

part distorted and confused fibres or mere crystals, with the remains

of the wood forming phragmata between them, when in other parts it

may show the most minute structures in perfect preservation? But

who would use the disintegrated portions to invalidate the evidence

of the parts better preserved? Yet this is precisely the argument

of Professors King and Rowney, and which they have not hesitated

in using in the case of a fossil so old as Eozoon, and so often

compressed, crushed, and partly destroyed by mineralization.

 

I have in the above remarks confined myself to what I regard as

absolutely essential by way of explanation and defence of the

organic nature of Eozoon. It would be unprofitable to enter into the

multitude of subordinate points raised by the authors, and their

theory of mineral pseudomorphism is discussed by my friend Dr. Hunt;

but I must say here that this theory ought, in my opinion, to afford

to any chemist a strong presumption against the validity of their

objections, especially since it confessedly does not account for all

the facts, while requiring a most complicated series of unproved and

improbable suppositions.

 

The only other new features in the communication to which this note

refers are contained in the "supplementary note." The first of

these relates to the grains of coccolite in the limestone of Aker,

in Sweden. Whether or not these are organic, they are apparently

different from _Eozoon Canadense_. They, no doubt, resemble the

grains referred to by Gümbel as possibly organic, and also similar

granular objects with projections which, in a previous paper, I have

described from Laurentian limestones in Canada. These objects are of

doubtful nature; but if organic, they are distinct from Eozoon. The

second relates to the supposed crystals of malacolite from the same

place. Admitting the interpretation given of these to be correct,

they are no more related to Eozoon than are the curious vermicular

crystals of a micaceous mineral which I have noticed in the Canadian

limestones.

 

The third and still more remarkable case is that of a spinel from

Amity, New York, containing calcite in its crevices, including a

perfect canal system preserved in malacolite. With reference to

this, as spinels of large size occur in veins in the Laurentian

rocks, I am not prepared to say that it is absolutely impossible that

fragments of limestone containing Eozoon may not be occasionally

associated with them in their matrix. I confess, however, that

until I can examine such specimens, which I have not yet met with,

I cannot, after my experience of the tendencies of Messrs. Rowney

and King to confound other forms with those of Eozoon, accept their

determinations in a matter so critical and in a case so unlikely.[AU]

 

[Footnote AU: I have since ascertained that Laurentian limestone found

at Amity, New York, and containing spinels, does hold fragments of the

intermediate skeleton of Eozoon. The limestone may have been originally

a mass of fragments of this kind with the aluminous and magnesian

material of the spinel in their interstices.]

 

If all specimens of Eozoon were of the acervuline character, the

comparison of the chamber-casts with concretionary granules might

have some plausibility. But it is to be observed that the laminated

arrangement is the typical one; and the study of the larger

specimens, cut under the direction of Sir W. E. Logan, shows that