life is dawn on the earth 29

life is dawn on the earth 29

replacement pseudomorphs, as understood by these authors, a mineral

species disappears and is replaced by another which retains the

external form of the first. Could it be shown that the calcite of the

cell-wall of Eozoon was once serpentine, this portion of carbonate

of lime would be a replacement pseudomorph after serpentine; but why

the portions of this mineral, which on the hypothesis of Messrs. King

and Rowney have been thus replaced, should assume the forms of a

foraminiferal skeleton, is precisely what our authors fail to show,

and, as all must see, is the gist of the whole matter.

 

"Messrs. King and Rowney, it will be observed, assume the existence

of calcite as a replacement pseudomorph after serpentine, but give

no evidence of the possibility of such pseudomorphs. Both Rose and

Bischof regard serpentine itself as in all cases, of pseudomorphous

origin, and as the last result of the changes of a number of mineral

species, but give us no example of the pseudomorphous alteration of

serpentine itself. It is, according to Bischof, the very insolubility

and unalterability of serpentine which cause it to appear as the

final result of the change of so many mineral species. Delesse,

moreover, in his carefully prepared table of pseudomorphous minerals,

in which he has resumed the results of his own and all preceding

observers, does not admit the pseudomorphic replacement of serpentine

by calcite, nor indeed by any other species.[AV] If, then, such

pseudomorphs exist, it appears to be a fact hitherto unobserved,

and our authors should at least have given us some evidence of this

remarkable case of pseudomorphism by which they seek to support their

singular hypothesis.

 

[Footnote AV: _Annales des Mines_, 5, xvi., 317.]

 

"I hasten to say, however, that I reject with Scheerer, Delesse

and Naumann, a great part of the supposed cases of mineral

pseudomorphism, and do not even admit the pseudomorphous origin of

serpentine itself, but believe that this, with many other related

silicates, has been formed by direct chemical precipitation. This

view, which our authors do me the honour to criticise, was set

forth by me in 1860 and 1861,[AW] and will be found noticed more

in detail in the _Geological Report of Canada_, for 1866, p. 229.

I have there and elsewhere maintained that 'steatite, serpentine,

pyroxene, hornblende, and in many cases garnet, epidote, and other

silicated minerals, are formed by a crystallization and molecular

re-arrangement of silicates, generated by chemical processes in

waters at the earth's surface.'[AX]

 

[Footnote AW: _Amer. Journ. Science_ (2), xxix., 284; xxxii., 286.]

 

[Footnote AX: _Ibid._, xxxvii., 266; xxxviii., 183.]

 

"This view, which at once explains the origin of all these bedded

rocks, and the fact that their constituent mineral species, like

silica and carbonate of lime, replace the perishable matter of

organic forms, is designated by Messrs. King and Rowney 'as so

completely destitute of the characters of a scientific hypothesis

as to be wholly unworthy of consideration,' and they speak of my

attempt to maintain this hypothesis as 'a total collapse.' How far

this statement is from the truth my readers shall judge. My views

as to the origin of serpentine and other silicated minerals were

set forth by me as above in 1860-1864, before anything was known

of the mineralogy of Eozoon, and were forced upon me by my studies

of the older crystalline schists of North America. Naumann had

already pointed out the necessity of some such hypothesis when he

protested against the extravagances of the pseudomorphist school,

and maintained that the beds of various silicates found in the

crystalline schists are original deposits, and not formed by an

epigenic process (_Geognosie_, ii., 65, 154, and _Bull. Soc. Geol.

de France_, 2, xviii., 678). This conclusion of Naumann's I have

attempted to explain and support by numerous facts and observations,

which have led me to the hypothesis in question. Gümbel, who accepts

Naumann's view, sustains my hypothesis of the origin of these rocks

in a most emphatic manner,[AY] and Credner, in discussing the genesis

of the Eozoic rocks, has most ably defended it.[AZ] So much for my

theoretical views so contemptuously denounced by Messrs. King and

Rowney, which are nevertheless unhesitatingly adopted by the two

geologists of the time who have made the most special studies of the

rocks in question,--Gümbel in Germany, and Credner in North America.

 

[Footnote AY: _Proc. Royal Bavarian Acad._ for 1866, translated in

_Can. Naturalist_, iii., 81.]

 

[Footnote AZ: _Die Gliederung der Eozoischen Formations gruppe

Nord.-Amerikas,--a Thesis defended before the University of Leipzig,

March 15, 1869_, by Dr. Hermann Credner. Halle, 1869, p. 53.]

 

"It would be a thankless task to follow Messrs. King and Rowney

through their long paper, which abounds in statements as unsound as

those I have just exposed, but I cannot conclude without calling

attention to one misconception of theirs as to my view of the origin

of limestones. They quote Professor Hull's remark to the effect that

the researches of the Canadian geologists and others have shown that

the oldest known limestones of the world owe their origin to Eozoon,

and remark that the existence of great limestone beds in the Eozoic

rocks seems to have influenced Lyell, Ramsay, and others in admitting

the received view of Eozoon. Were there no other conceivable source

of limestones than Eozoon or similar calcareous skeletons, one might

suppose that the presence of such rocks in the Laurentian system

could have thus influenced these distinguished geologists, but

there are found beneath the Eozoon horizon two great formations of

limestone in which this fossil has never been detected. When found,

indeed, it owes its conservation in a readily recognisable form to

the fact, that it was preserved by the introduction of serpentine

at the time of its growth. Above the unbroken Eozoon reefs are

limestones made up apparently of the debris of Eozoon thus preserved

by serpentine, and there is no doubt that this calcareous rhizopod,

growing in water where serpentine was not in process of formation,

might, and probably did, build up pure limestone beds like those

formed in later times from the ruins of corals and crinoids. Nor

is there anything inconsistent in this with the assertion which

Messrs. King and Rowney quote from me, viz., that the popular notion

that _all limestone formations_ owe their origin to organic life is

based upon a fallacy. The idea that marine organisms originate the

carbonate of lime of their skeletons, in a manner somewhat similar to

that in which plants generate the organic matter of theirs, appears

to be commonly held among certain geologists. It cannot, however,

be too often repeated that animals only appropriate the carbonate

of lime which is furnished them by chemical reaction. Were there

no animals present to make use of it, the carbonate of lime would

accumulate in natural waters till these became saturated, and would

then be deposited in an insoluble form; and although thousands of

feet of limestone have been formed from the calcareous skeletons

of marine animals, it is not less true that great beds of ancient

marble, like many modern travertines and tufas, have been deposited

without the intervention of life, and even in waters from which

living organisms were probably absent. To illustrate this with the

parallel case of silicious deposits, there are great beds made

up of silicious shields of diatoms. These during their lifetime

extracted from the waters the dissolved silica, which, but for their

intervention, might have accumulated till it was at length deposited

in the form of schist or of crystalline quartz. In either case the

function of the coral, the rhizopod, or the diatom is limited to

assimilating the carbonate of lime or the silica from its solution,

and the organised form thus given to these substances is purely

accidental. It is characteristic of our authors, that, rather than

admit the limestone beds of the Eozoon rocks to have been formed like

beds of coralline limestone, or deposited as chemical precipitates

like travertine, they prefer, as they assure us, to regard them as

the results of that hitherto unheard-of process, the pseudomorphism

of serpentine; as if the deposition of the carbonate of lime in

the place of dissolved serpentine were a simpler process than its

direct deposition in one or the other of the ways which all the world

understands!"

 

 

(C.) Dr. Carpenter on the Foraminiferal Relations of Eozoon.

 

In the _Annals of Natural History_, for June, 1874, Dr. Carpenter

has given a crushing reply to some objections raised in that journal

by Mr. Carter. He first shows, contrary to the statement of Mr.

Carter, that the fine nummuline tubulation corresponds precisely in

its direction with reference to the chambers, with that observed in

Nummulites and Orbitoides. In the second place, he shows by clear

descriptions and figures, that the relation of the canal system to

the fine tubulation is precisely that which he had demonstrated in

more recent nummuline and rotaline Foraminifera. In the third place

he adduces additional facts to show that in some specimens of Eozoon

the calcareous skeleton has been filled with calcite before the

introduction of any foreign mineral matter. He concludes the argument