IMAGE EVALUATION
TEST TARGET (MT-3)

1.0

I.I

1.25

-m iiiiM

■ IM IIIIIZ2

2.0

LA. IIIIII.6

•>."

/,.

/!%

Photographic

Sciences
Corporation

^R)

•1?

33 WEST MAIN STREET

WEBSTER, NY 14580

(716! 872-4503

CIHM/ICMH

Microfiche

Series.

CIHM/ICMH
Collection de
microfiches.

Canadian Institute for Historical Microreproductions Institut Canadian de microreproductions historiques

1980

Technical and Bibliographic Notes/Notes techniques et bibliographiques

The Institute has attempted to obtain the best
original copy available for filming. Features of this
copy which may be bibliographically unique,
which may alter any of the images in the
reproduction, or which may significantly change
the usual method of filming, are r acked below.

L'Institut a microfilm^ le meilleur exempldire
qu'il lui a 6t6 possible de se procurer. Les details
de cet exemplaire qui sont peut-dtre uniques du
point de vue bibliographique, qui peuvent modifier
une image reproduite, ou qui peuvent exiger une
modification dans la mdthode normale de filmage
sont indiquds ci-dessous.

D
D

Coloured covers/
Couverture de couleur

Covers damaged/
Couverture endommagde

Covers restored and/or laminated/
Couverture restaur6e et/ou pellicul6e

Cover title missing/

Le titre de couverture msnque

Coloured maps/

Cartes g^ographiques en couleur

Coloured ink (i.e. other than blue or black)/
Encre de couleur (i.e. autre que bleue ou noire)

Coloured plates and/or illustrations/
Planches et/ou illustrations en couleur

Bound with other material/
Reli6 avec d'autres documents

Tight t. nding may cause shadows or distortion
along interior margin/

La reliure serree peut causer de Tombre ou de la
distortion le long de la marge int^rieure

BlanK leaves added during restoration may
appear within the text. Whenever possible, these
have been omitted from filming/
II se peut que certaines pages blanche? ajout6es
lors d'une restauration apparaissent dans le texte,
mais, lorsque cela 6tait possible, ces pages n'ont
pas 6t6 film^es.

Additional comments:/
Commentaires suppl^mentaires;

□ Coloured pages/
Pages de couleur

D
D

Pages damaged/
Pages endommag^es

Pages restored and/or laminated/
Pages restaurdes et/ou pellicul^es

Pages discoloured, stained or foxed/
Pages ddcolor^es, tachetdes ou piqu^es

Pages detached/
Pages ddtach^es

Showthrough/
Transparence

I I Quality of print varies/

Quality in^gale de I'impression

Includes supplementary material/
Comprend du materiel supplementaire

Only edition available/
Seule Edition disponible

Pages wholly or partially obscured by errata
slips, tissues, etc., have been refilmed to
ensure the best possible image/
Les pages totalement ou partiellement
obscurcies par un feuillet d'errata, une pelure,
etc., ont 6t6 film6es d nouveau de fapon i
obtenir la meilleure image possible.

This item is filmed at the reduction ratio checked below/

Ce document est filmd au taux de reduction indiqud ci-dessous.

10X

14X

18X

22X

26X

30X

12X

16X

20X

24X

28X

32X

The copy filmed here has been reproduced thanks
to the generosity of:

National Library of Canada

L'exemplaire film6 fut reproduit grice d la
gdndrositd de:

Bibliothdque nationale du Canada

The images appearing here are the best quality
possible considering the condition and legibility
of the original copy and in keeping with the
filming contract specifications.

Les images suivantes ont 6t6 reproduites avec le
plus grand soin, compte tenu de la condition et
de la nettet6 de l'exemplaire film6, et en
conformity avec les conditions du contrat de
filmage.

Original copies in printed paper covers are filmed
beginning with the front cover and ending on
the last page with a printed or illustrated impres-
sion, or the back cover when appropriate. All
other original copies are filmed beginning on the
first page with a printed or illustrated impres-
sion, and ending on the last page with a printed
or illustrated impression.

Les exemplaires originaux dont la couverture en
papier est imprim6e sont filmds en commengant
par le premier plat et en terminant soit par la
dernidre page qui comporte une empreinte
d'impression ou d'illustration, soit par le second
plat, selon le cas. Tous les autres exemplaires
originaux sont film^s en commengant par la
premidre page qui comporte une empreinte
d'impression ou d'illustration et en terminant par
la dernidre page qui comporte une telle
empreinte.

The fast recorded frame on each microfiche
shall contain the symbol —*■ (meaning "CON-
TINUED "), or the symbol V (meaning "END ").
whichever applies.

IJn des sy( .boles suivants apparaitra sur la
dernidre image de cheque microfiche, selon le
cas: le symbole —^ signifie "A SUIVRE", le
symbole V signifie "FIN".

Maps, plates, charts, etc., may be filmed at
different reduction ratios. Those too large to be
entirely included in one exposure are filmed
beginning in the upper left hand cornei', left to
right and top to bottom, as many frames as
required. The following diagrams illustrate the
method:

Les cartes, planches, tableaux, etc., peuvent dtre
filmds d des taux de reduction diffdrents.
Lorsque le document est trop grand pour etre
reproduit en un seul cliche, il est film6 d partir
de Tangle sup6rieur gauche, de gauche d droite,
et de haut en bas, en prenant le nombre
d'images ndcessaire. Les diagrammes suivants
illustrent la mdthode.

32X

1 2 3

4 5 6

/-/

L ^ '

/ a.>r* V t

CHEMICAL GEOLOGY.

MR. T. STERRY HUNT'S

REPLIES TO THE CRITICISMS

MR. DAVID FORBES.

^m^tm

•■P^^^^in

TftOT-

A NOTICE OF THE CHEMICAL GEOLOGY OF Mr. D. FORBES.

BY T. STERRY HUNT, F. R. S.

The Geological Magazine for October last contains a criticism by
Mr. Davi'l Forbes of certain views put forward by me in a lecture
delivered before the Royal Institution of Great Britain on the Slst
of May, 1867. Of this lecture a short-hand report appears in this
Magazine for August, besides which a condensed report, revised
by myself, is published in the proceedings of the Institution, in the
Chemical News for June 21st, and in three French translations in the
Revue des Cours Scientijiques, Les Mondi, and Cosmos. The Chemical
News for October 4th contains a criticism of my lecture by Mr.
Forbes, to which I have replied in a communication recently
addressed to that Journal.

In the lecture in question, I endeavored to bring together the
results of modern investigations in physics, chemistry, mathema-
tics and astronomy, and to construct from them a scheme which
should explain the development of our globe from a supposed
i»tensely heated vaporous condition down to the present order of
things. I could not pretend to discuss from their various stand-
points, all the conclusions arrived at by different investigators,
inasmuch as, even had my attainments permitted, the limits of an
hour's lecture would have proved far too short.

In regard to the structure of the earth I alluded to two views,
one of which supposes a liquid globe covered with a thin crust of
solidified rock, generally estimated at from twenty to thirty miles
in thickness, while the other regards the earth, if not solid to the
centre, as having a crust at least several hundred miles in thickness,
and of such solidity and rigidity as to be, so far as superficial
phenomena are concerned, inert as if in a solid state. To this
latter view, I incline, and I cited in support of it the conclusions of
Hopkins from the phenomena of precession and nutation, the in-
vestigations of Archdeacon Pratt on the crushing effect of ini-
mense mountain masses like the Himmalayah, and the deductions
of Sir Wm. Thompson from the phenomena of the tides, showing
the great rigidity of the earth, as so many concurrent evidences
that our planet, if not actually solid to the centre, has a crust far
thicker than can be accounted for by the theory of a liquid
globe covered only with a crust resulting from superficial cool-
ing. This latter view, which was deduced from Cue increilse of tem-
perature observed in descending into the earth, is in conflict with
the various mathematical and physical considerations above no-
ticed, and it becomes necessary to revise the older notions of the
conditions of a cooling globe.

The investigations of Charles Deville and of Delesse, as well as
the earlier ones of Bischof, show that the density of fused rocks is
very much less than that of the crystalline minerals of which they
are composed. From this we may naturally conclude that the
crystalline compounds which would separate by slow cooling from
a bath of molten rock would gravitate toward the centre, as Sae-
mann has already justly observed, (Bull. Soc. Geol. de Fr. Feb. 4.
1861.) In opposition to this view, Mr. Forbes appeals to the results
seen in a small scale in the cooling of melted metals, etc., — where
a crust forms over the surface. It must, however, be considered
that the conditions presented by a small vessel full of a liquid
congealing in an atmosphere greatly below its own temperature,
and having a crust growing out from and supported by the sides
of the vessel, are widely different from those of a liquid globe
slowly cooling beneath a very dense and intensely heated atmos-
phere. In such a case, with a bath of materials similar to those
forming our present rock-crust, the crystalline minerals of which
have been shown by Deville to be from -^g to | heavier than the
liquid mass, these, as they separated, would sink as naturally as
the crystals which form at the surface of an evaporating basin of
brine. The analogy holds good, since the denser crystals formed

at the surface, whether by evaporation or by cooling, obey the
inevitable laws of gravity.

Mr, Forbes next proceeds to some considerations drawn from the
mean density of the earth, which being about 5.3, is twice that of
the average specific gravity of th3 solid materials known at the
surface. Admitting that a solid crust of specific gravity 2.65 were
to form at the surface of a liquid of density 2.3, and in obedience
to natural laws, to sink therein, our critic conceives that, in its
descent, it would meet with a denser liquid stratum. lie supposes
a liquid globe " becoming rapidly denser in descending, as the
pressure increased by the superincumbent column of liquid mat-
ter," and he tells us, in a note, that we may admit a density of
" nearly 10.7 for the middle zone and about 18.8 for the centre." .
(page 435). Two pages farther on he has completely changed his
mind, for he tells us that " experimental research tends to show
that a limit is soon reached beyond which the compression or
increase of density becomes less and less in relation to the force
employed," and concludes that there are strong reasons for believ-
ing that the central jmrts of the earth "must consist of much dens-
er bodies, such as metals and their metallic compounds," which
he farther on exjilains may mean " dense sulphids."

To which of these two views does Mr. Forbes mean to hold, that
of a rapidl.y and constantly increasing density from i>ressure,
or that in which, limiting the condensing effect of pressure,
he seeks to explain the density of the earth by a nucleus of heavy
metallic compounds? The latter is seemingly an after- thought of
the critic, suggested by some notion of the jirinciple involved in
the augmentation by pressure, of the fusing point of bodies
which expand m melting. As was shown by James Thomp-
son, the effect of pressure upon ice (and naturally ujion such me-
tals and metallic alloys as, like it, contract in melting,) would be to
reduce its melting point, a fact which has been exjjerunentally
established for ice. Reasoning from the same principle. Sir Wm.
Thompson deduced the conclusion that a reverse effect should
result from pressure for all such solids as expand in melting, that
is to say, that their points of fusion would be raised, a conclusion
verified by the experiments of Bunsen and by those of Fairbairn
and Hopkins. From some apparent irregularities in these results,
and from the fact that certain of the substances submitted to
experiment were bodies of the carbon series, which Mr. Forbes calls
" organic," he argues against the conclusions which depend upon
a well defined physical law. In the case of the fusible alloys tried

by Mr. Hopkins, it is to be remarked that most of these bodies,
like ice, expand in cooling, and consequently should not have their
melting points raised by pressure. For the memoirs of James and
William Thompson, see Trans, Royal Soc. Edin. XVI, part 5, and
L. E. D. Philos. Mag. [3] XXXVII, 125. A simple and popular
exposition of the principle, and of Mr. Hopkins's argument there-
from, for the solidity of the globe, will be found in the fourth of
Tyndal's lectures on Heat as a Mode of Motion. See also Sorby's
Bakerian lecture for 1863, cited farther on. Mr. Forbes must con-
sider that just so far as he admits the condensing power of the pres-
sure of the superincumbent mass, he increases the difficulty of
maintaining that rocky mass in a liquid state.

The condensing effect of pressure was by Dr. Young estimated
to be sufficient to reduce a mass of granite at the earth's centre to
one-eighth its bulk at the siuface, which would give to the earth
a mean density equal to twelve or thirteen times that of water.
This consideration has led a recent writer in the London Athen-
(Bum to conclude with Herbert Spencer, that our earth .and the
other planets may be only shells of varying thicknesses, enclosing
a central cavity filled with vaporous matter, by which hypothesis
we may explain the apparently feeble density. See Mr. Spencer's
essay on the Nebular Hypothesis in the Westminster Review for
July 1858. It may be observed that his view which supposes con-
densation to have resulted in the formation of a solid shell around
a gaseous nuclent, is not incompatible with my scheme, which is
simply opposed to a liquid interior. See also the note of Mr.
Barker in this Magazine for September last, page 426. Leaving
Mr. Forbes to settle these vexed questions, we may remark that
in case we suppose condensation of the gaseous globe to have com-
menced either at the centre or around a gaseous nucleus, it is
probable that solidification from pressure must have taken place
long before the liquefaction of earthy matters was complete.

But if we adopt Mr. Forbes' s second hypothesis that pressure would
not materially augment the density nor raise the melting point of
the fused mass, what grounds has he for assuming, as he does, that
there occurred a separation of the liquid into zones of different
densities ? That metallic sulphids could be formed at an elevated
temperature, by condensation from an atmosphere containing an
excess of oxygen, is contrary to all that we know of chemical affini-
ties ; sulphurous acid and metallic oxyds would be the results so
soon as the temperature fell below that of dissociation. As for the
noble metals, whose compounds with oxygen are decomposed at

elevated temperatures, their great volatility, as compared with
earthy and metallic oxyds, would keep them in the gaseous form till
the last stage of precipitation of earthy oxydized matters, wlien by
far the greater part of the globe was probably solidified. Hence
we now find them in the earth's superficial crust, instead of being,
as Mr. Forbes would suppose, carried to the centre of the planet.
Judging from what we know of chemical affinities, and of the
proportions of the elements now existing in the superficial parts
of the globe, we cannot conceive anything else than the production
of a homogeneous oxydized silicated mass, upon which, at a late pe-
riod, would b .recipitated the noble metals. From this mass, while
yet liquid, there might take a separation of various crystalline com-
pounds, by a process analogous to that by which pui-e lead separ-
ates from the bath of the argentiferous alloy in Pattinson's process,
as Fournet has already suggested, (Gcol. Lyonnaiso, 18G2, page
398). The last congealed and lighter portion of our glooo, with
which alone we have to do, was, probably, a sort of mother-licjuor
from which, during its slow cooling, compounds of various consti-
tution and density may well have crystallized. In furnace opera-
tions, it is true, we may obtain, besides silicated slags, a dense stra-
tum of reguline metals, sulphids or arsenids on the one hand, and a
lighter one of saline sulphates or chlorids on the other. But neither
of these classes of compounds was possible in the cooling globe,
the reguline matters for reasons just given, and the saline com-
pounds, for reasons yet to be explained.

I have in my lecture set forth that the earth's superficial crust
must have been composed of silicates of the metallic, earthy and
alkaline bases, surrounded by a dense acid atmosphere of hydro-
chloric, sulphurous and carbonic acids, besides watery vapor, ni-
trogen and oxygen. These chemical combinations are such as
would naturally result from the affinities brought into play at
the elevated temperatures then prevailing, in virtue of which all
those elements capable of forming fixed and stable compounds with
oxygen would be precipitated as oxyds. In these conditions, as
already said, no metallic sulphids would be formed, and the whole
of the sulphur would be found as sulphurous acid. In like man-
ner the production of alkaline chlorids under such conditions, is
inconceivable, since in the conjoined presence of oxygen, hydrogen,
and silicon or silica, an alkaline silicate and hydrochloric acid
would result. Even, if, as Mr. Forbes supposes, chlorid of sodium
were to be formed in the heated atmosphere, it would be precipitated
into a bath of fused silicates, covered by an intent ely heated at-

mosphere containing water, or mingled oxygen nnd hydrogen
gases, and would immediately undergo the same decomposition
that takes place when the vapors of common salt arc diffused
through a potter's kiln, or, as in Mr. Qossage's new soda-process,
are passed with steam over red-hot flints. In both cases silicates
of soda are formed with separation of hydrochloric acid.

These considerations lead to the conclusion that after all the
more fixed elements were precipitated, tht hole of the chlorine
would finally remain in the partially cooled atmosphere as hydro-
chloric acid, and the whole of the sulphur as sulphurous acid, to-
gether with a large proportion of oxygen, since we find this element
in the form of sulphate and not as sulphite in the sea-waterS. Mr.
Forbes does not, it seems, believe that an excess of oxygen could
exist in an atmosphere highly charged with sulphurous acid, and
elsewhere (in the Chemical News), he tells that it is, " if not impos-
sible, at least, highly improbable that such a heated atmosphere
containing sulphurous acid, hydrochloric acid, with oxygen and
nqiieous vapor could exist," the elements being in his opinion,
incompatible. He is aware that at certain temperatures sulphur-
ous acid and oxygen unite, in the presence of water, to form
oil of vitriol, but he forgets that at a higher temperature this com-
pound is again resolved into water, sulphurous acid and oxygen ;
and that one of the best processes for preparing the latter gas on
a large scale, is by this decomposition of sulphuric acid, and the
subsequent removal of the sulphurous acid from the cooled gaseous
mixture. In the opinion of Mr. Forbes, as set forth in the Chemical
News, the sulphurous and hydrochloric acids would decompose
each other, in the presence of watery vapor (though every chemist's
experience teaches him the contrary ; ) another reason for holding
that my supposed atmosphere was impossible. Unfortunately for
his opinion, however, it happens that large quantities of precisely
such an atmosphere are disengaged from various volcanic vents.
To cite one among many examples examined by Charles Deville
and Leblanc (Ann. de Ch. et Phys. [3]LII. pp. 5-63) &fumerolle of
Vesuvius yielded in June, 1856, a mixture of highly heated steam,
hydrochloric acid, sulphurous acid and air containing 18.7 per cent
of oxygen. The sulphurous acid was equal to 2.6 per cent, of the
air, and the amount of hydrochloric acid was about five times as
great. Traces of sulphuric acid were found in the water condensed
from this steam, doubtless formed by the slow combination of the
sulphurous acid and oxygen, and I may state for the information
of Mr. Forbes, that it was doubtless by a similar reaction that the sul.

WNI

mmmm

phurous acid became eliminated from the primeval atmofiphere.
We have here, I may remark, an illu.stration of the fact upon which
I have elsewhere insisted, that volcanoes reproduce, on a limited
scale, the conditions of the primeval earth, not only in their solid
but in their gaseous products.

Mr. Forbes next asserts that, according to me, " the hydrochloric
acid in the i)rimeval atmosphere was derived from the mutual
reactions of sea-salt, silica and water," (page 438) and then charges
the author with the folly of <' supposing the pre-existence of com-
pound bodies in a case where he had previously informed us that
there were only dissociated elements engaged." Mr. Forbes knows
better than this, or at least did know better when he wrote his
criticism on my lecture in the Chemical Neivs of Oct. 4, for he here
quotes my own words, when, in descrfbing the cooling globe, the
conditions through which it must have passed, and the affinities
brought into play, I say the products must have been '^just what
would now remit if the solid land, sea, and air, weremade to react upon
each other under the influence of interne heat.^^' It is so difficult to
characterize properly such a wilful perversion of an author's words,
that I must leave the task to my readers. What follows in Mr.
Forbes" s paper as to chlorids, etc., I have already discussed and dis-
posed of. The theory of the constitution of tlie solid globe next put
forward by Mr. Forbes, borrowed from Phillips, Durocher and Von
Waltershausen, is also, as I conceive, met by the argument in the
previous pages. When, however, he comes to the atmosphere sur-
lounding his primitive globe, Mr. Forbes puts forward a scheme
which is strikingly original. He supposes around the ''solidified
crust " a dense vapor consisting chiefly of chlorid of sodium,
" above this a stratum of carbonic acid gas, and then of water in
the form of steam, whilst the oxygen and nitrogen would be ele-
vated still higher," (p. 439), probably, also, separated in the order
of their densities. In explanation of this order he tells us in a
note that the zone of carbonic acid gas would be heavier than that
of steam, and should therefore come below it, but he forgot that
oxygen and nitrogen (or atmospheric air) are also both heavier
than steam, and should consequently be placed below the zone of
watery vapor. The specific gravities of carbonic acid and steam
are respectively 1.525, and 0.624, air being l.O(M). But, apart from
this absurd mistake, what shall be said to a man who ignores com-
pletely the laws of the diffusion of gases? WillMr. Forbes kindly ex-
plain why, in our present atmosphere, the same elements, namely,
oxygen, nitrogen, carbonic acid gas and watery vapor, are com-

mmmmmm

mingled, instead of being, as he would have them, arranged in
separate zones ?

I have said in my lecture that the first ocean waters would hold
in solution salts of alumina and the heavy metals, all of which
would be precipitated before the separation of carbonate of lime
commenced. In such event, says Mr. Forbes ^^ geologisti^, thovgh as
yetunsuccesufulin doing so, might stiJl hope io Jindbeds of almnina or
of the metallic oxyds or carbonates alluded to, in the older strata,
vis no beds of such character are known to occur in nature,^' he re-
gards my view with distrust. Known to Mr. Forbes ! Has he nev«r
heard of beds of emery, which are chiefly crystalline alumina, and
which occur in the crystalline limestones of Asia Minor,and in the old
crystalline schists of New England ? Is he ignorant that the beds
of bauxite, so abundant in the Mediterranean basin, and used in the
manufacture of aluminium, consist chiefly of hydrated alumina ?
"To console Mr. Forbes however, I will say that I believe these beds of
emery and of bauxite to have been formed by secondary and subse-
quent reactions, and that we have Uvnvhere exposed to view the
first, dei^osited beds, which are everywhere destroyed or burietl
under more recent strata. When he remembers that the oldest
known series of rocks, the Laurentian, consists of quartzites, lime-
stones, and gneiss, evidently of sedimentary origin, and derived from
still older sedimentary rocks, ne will understand why he cannot
hope to discover the first deposits of alumina Jor metallic oxyds.
These, however, in most cases, have doubtless, by mechanical sub-
division, or by solution, been subsequently diffused, and enter
into the composition of later rocks.

In a note to this iniragrapii, Mr. Forbes inquires what became of
the sulphurous acid of the early atmosphere ; as I have already told
him, it doubtless became changed into sulphuric acid and passed
into the sea. He then says ''it may safely be asserted that there
is fully as much (if not more) sulphur than chlorine" in nature,
and that according to my hypothesis, the sea would become a
solution of sulphate of soda. Very safely asserted indeed, since Mr.
Forbes takes care to tell us that the sulphur in the form of dense
metallic sulphids went to the centre of the oartli, which 1 liave
shown, I think, good reasons for not believing. As it is, we have
only to consider the (Uiantities of sulphids and sulphates in the rocks
and waters to see the absurdity of his remarks.

lie next proceeds to discuss the theory of the origin of carbo-
nate of lime. I have said that with the exception of that derived
from the subauia) decomposition of primitive calcareous silicates,

all of the carbonate of lime of the earth's surface has been formed
from the decomposition of the soluble lime-salts of the sea, by-
carbonate of soda (and other soluble carbonates.) I, moreover, lay-
down the proposition that "animals can only appropriate the car-
bonate of lime already formed." In the face of these quotations,
cited by Mr. Forbes, he says, as if charging me with holding the
view, that if limestones were "formed by precii)itation, they
would have, from the moment of their deposition, a tlecided crys-
talline structure," while "Sorby's microscopical researches prove
satisfactorily that all limestones, from the most ancient up to the
most recent, are solely formed of the debris of organisms;'^ this
will probably be surprising news for Mr. kSorby, and a decisive
blow for those who question the organic nature of Eozoon. I am
prepared to go as far as any reasonable man in asserting the or-
ganic origin of limestones, and have, as every one must see, implied
the intervention of organic life, wlien I say, "animals appropriate
the carbonate of lime, etc." The question is, however, wneuce
comes the carbonate of lime to supply the wants of these animals ?
Mr. Forbes declares that " zoologists believe that marine animals can
utilize the other salts of lime existing in the ocean," evidently the
sulphate or the chlorid of calcium once so abundant there. Will Mr,
Forbes or the zoologists explain what has become of the acids once
combined with the lime which has built w\-> the thousands of fees
of limestone, chiefly fossilifevous, which are found in the earth's
crust? The only plausible chemical ex])lanation is that wliich I
have given, namely : that the chlorid of calcium has been decom-
posed by carbonate of soda derived from decaying feldspathic
rocks, giving rise thereby to common salt and to the carbonate of
lime which has supplied the marine animals.

As regards the question of the origin of dolomites, which Mr.
Forbes next proceeds to notice, he will do well to consult my pajier
on the subject in the American Journal of Science for July, 1866,
([2] XLll, 4'.)). In this, at §112, he will see that, apai't from the for-
mation of stratified sedimentary dolomites, 1 insist upon tlie
frequent occurrence of dolomite as a mineral of secondary deposi-
tion, lining drusy cavities, filling veins, and even the moulds of
fossil shells. To such cases the observations of .Sorby may possibly
refer, I can find no other account of his researches than the brief
note in the Proc. of the Brit. Assoc, foi- 1856, cited by Mr. Forbes.
Although I have a great respect for Mr. Sorby as an investigatoi-,
I have very little for the old theory of dolomitiziition of sedimen-
tary limestones. No one who has carefully studied, as I have done for

years, the distribution and association of the great beds of dolomite
wliich occur in the Lower Silurian rocks of Canada and New Eng-
land, can for a moment admit that these are the products of
subsequent alteration. Repeated alternation of pure blue lime-
stones with reddish ferruginous dolomites, interrupted beds and
patches of these enclosed in the former, the line of demarcation
sharply drawn, and finally conglomerates in which pebbles of pure
limestone are enclosed in beds of dolomite, are incontrovertible
evidences against the theory of the dolomitization of limestones,
and in tavor of the deposition of dolomites as magnesian sedi-
ments. (Geology of Canada, 1863, page 612).

Mr. Forbes, in a note, insinuates that I am unaware of the
various speculations and theories which have been put forward to
explain the supposed origin of dolomite by alteration. Although
the stratigraphical relations of dolomite, as described above, com-
pletely contradict this h,yi>o thesis of its origin, at least in the great
majority of cases, Mr. Forbes will find tliat the observations and
speculations of Haidinger, VonMorlot, Marignac, and others, on this
subject have been fully discussed and made the subject of multi-
plied experiments by me in a memoir published in 1859, {Amer-
Jour. Science, [2] XXVIII. 170, .30"),) and later in the paper quoted
above, and that I have shown by many experiments that the
action of sidphate of magnesia on carbonate of lime, alluded to by
llaitUnger and Von Moi-lot before Ilarkness or Regnault, does not
give rise to dolomite, but to carbonate of magnesia, wliich remains
mechanically intermiii/^led with sulphate of lime ami any excess of
cai'bonate of linie.

Some of the results of my prolonged study of certain of the salts
of lime and magnesia, which are, for the most part, set forth in the
papers j'ust referred to, were, says Mr. Forbes, by me considered
worthy of being presented to the French Academy {Comptes lien-
dus, April 22, IHfiT), although he declares the reactions therein des-
\cribed, to have been for more than twenty years in general
application, on a large scale in (ireat Britain for the manufacture
of magnesia salts. Here it becomes difficult to admit the plea of
ignorance wliich suggests itself for most of Mr. Forbes's previous
error.s and mis. statements. I have, in the note to the French
Academy, above referred to, pointed out the following facts, dis-
covered by my investigations of the salts of lime and magnesia: —
1st. That bicarbonate of lime, at ordinary temperatures, de-
composes solutions of sulphate of soda and suljthate of mag-
nesia, with formation of sulphate of lime and bi-carbonates.

ip m

2nd. That from mingled solutions, of sulphate of magnesia and
bi-carbonate of lime, there separates by evaporation, crystalline
gypsum, and, subsequently, a hydrous carbonate of magnesia ; the
bi-carbonate, of this base being, as is well known, very much more
soluble than either the sulphate or the bicarbonate of lime. 3rd.
That this separation of gypsum is favored and rendered more
complete by an atmosphere impregnated with carV)onic acid gas ;
and 4th, that mixtures, in due proportions, of precipitated carbo-
nate of lime and hydrous carbonate of magnesia, when gently
heated under pressure, and in the presence of water, unite to foim
the anhydrous double carbonate, dolomite. These are the re-
actions which I described to tlie French Academy as new, and as
forming the basis of a reasonable theory of the origin of gypsums
and of dolomites. I now demand Mr. Forbes to make good his
bold assertions to the contrary, oi' to show that any one of them
has been employed for the last twenty years in the manufacturo
of magnesian salts.

Mr. Foi'bes then proceeds to inform us that " the grand develop-
ment of magnesian limestones, dolomites, and gyi)seous Vjeds,
really took place in an ej)och when numerous air-breatliing
animals, both vertebi*ates and invertebrates, lived upon tlie face
of the globe." Is Mr. Forbes aware that a large proportion of the
4,750 feet of limestone measured by Sir William Logan in
Canada, and constituting the three great limestone formations of
the old Laurentian system, is magnesian, and often, through great
thicknesses, a pure dolomite, that a large part of the Lower
Silurian system, and nearly the whole of the LTpper Silurian, from
the St. Liiwrence to the Mississippi, consists of dolomite, and
embraces great gypsum beds ; and, finally, that immense gyp-
sum deposits found, at intervals, from Nova Scotia to the Ohio,
lie at the base of the Carboniferous system, in whicli latter
only are found the Jir.st rcmaiiui of air-breathing vestebrates?
It is dangerous to generalize from the geology of the British
Islands, or of a small })art of Europe. Moieover, will Mr. Forbes
attempt to demonstrate that at tlie time when Tertiary gyitsums
were deposited in the Paris basin, there did not yet remain suffi-
cient carbonic aci<l in the air to modify its chemical action on
solutions of bicarbonate of magnesia, and give lise to the asso-
<',iated dolomites, which 1 was the first to discover in that posi-
tion ?

We now, in the language of Mr. Forbes, api)roach the question
"of the igneous origin of eruptive rocks and of granite in particu-

•or*

^ssmf^K^n^m^'fmm^Kmm^immm'm^mim''

':i i

lar." I asserted in my lecture the non-igneous origin of granite,
maintaining that "the composition oi the fused crust would have
excluded free silica," and "that granite is in every case a rock of
sedimentary origin, as it includes in its composition quartz, which,
so far as we know, can only be generated by aqueous agencies, and
at comparatively low temperatures." With regard to the first of
these statements, it is to be observed, that the primitive crust,
holding, as we have seen, in the form of silicates, all the soda, lime,
and magnesia which now appear in other combinations, must have
been a highly basic rock; moreover, even, were it much richer in
silica than we can suppose it to have been, there is no reason to
believe that free silica, in the form of quartz, ever did or ever could
crystallize from a fused slag, such as this primitive rock must have
been. Quartz, in the shape of rock-crystal, or flint, when fused, or
even when long exposed to a heat much below its melting point, is
changed into an i- meric modification of silica, analogous to, if not
identical with ojml, and distinguished fiom quartz by a much less
specific gravity, (about 2-2 instead of 2-65), the absence of crystal-
line structure, and a much greater solubility in alkalies and hydro-
fluoric acid. Silica crystallized in the form of quartz, ha&, ic is
true, been repeatedly obtained by different reactions, but never
hitherto, except in the presence of heated water or of watery vapor.
Heinrich Eose, to whom we are indebted for a careful study of
this subject records, that Gustaf Rose, having submitted to par-
tial fusion a granite, rich in quartz, obtained a glass or obsidian,
in wliich were enclosed unmelted jiortions of the (juartz, con-
verted, liowevor, into the less dense anil more soluble opal-like
form. These facts in ttie history of silica were regarded by II.
Rose, as decisive against the notion of the igneous origin of
granite, which he concludes to be incompatible with the actual
state of our chemical knowledge, llis paper on this subject,
which should be read by every geologist, appeared in Poggen-
dorfs Aimalen for September, 1859, and a careful abstract of it will
be found in the L. E. & D. Philos, Mag. for Jan. 1860. ( [4] XIX. 32.)
The new view of the origin of granite, which is there cited, as main-
tained " particularly by Mr. Sterry Hunt," is, that all granite rocks
are derived from the alteration of sediments, containing besides
feldspathic or argillaceous elements, quartz, derived, as I have ex-
plained, by the action of acid solutions at high temperatures on
the primitive crust of silicates.

The geological evidences are multiplied that gneiss, which does
not dirtier mineralogically from granite, and in its coarser varieties

Pv^ieviVBP

is constantly confounded with it, is the result of the alteration in
siiA of sedimentary rocks consisting of quartz with feldspathic or
argillaceous matters, the debris of jire-existing rocks. Moreover,
it is demonstrable that these stratified sediments have been soft-
ened, and while in such a condition, disjilaced or extravasated, and
have thus taken the form of exotic or eruptive rocks. Having by
this or other means lost the mechanical evidences of their former
stratified condition, they are called granites. The same view is,
according to me, applicable to dolerites, diorites and trachytes.
Modern lavas have no other origin, but take a different form,
because they come to the surface and are rapidly cooled, instead
of being slowly solidified under the pressure of superincumbent
strata. The fact that every eruptive or exotic rock (with the ex-
ception of certain rapidly cooled lavas) has its mineralogical equi-
valent among indigenous crystalline rocks, that is to say among
sedimentary strata of chemical oi' niechanical origin, is a powerful
argument in support of the view here put forward. In connection
with this, 1 have shown that a combination of chemical and me-
chanical agencies naturally and inevitably leads to the division
of aqueous sediments into the two great types to which lithologists
refer all eruptive rocks, namely, the acid, granitic or trachytic, and
the basic, doleritic groups, which are sujiposed to form the two
zones of igneous rock imagined by Phillips, and since insisted
upon by Durocher, Bunsen and Forbes. As all of these crystal-
line rocks are, according to my hypothesis, ancient sediments, it
follows that water has been present among them from their first
deposition, and during all the subsequent processes of their heat-
ing, softening, ciystallization and ejection — a view constantly
insisted upon by me, and in accordance with the ideas maintained
by Scheerer and subsequently by Sorby. This theory of igneous
rocks, although suggested by Keferstein in 1834, and by Sir J. F.
W. Herschel in 1837, has been elaborated by me in various papers
for the past ten years.

See Theory of Igneous Rocks and Volcanos, Canadian Journal,
March, 1858 ; some Points in Chemical (Jeology, Qnar. Jour. Geol.
Soc. Nov. 1859; Chemistry of the Earth, Compfes Jiemlus, , June 9ih,
1862 ; Chemistry of Metamorpliic Rocks, Dublin Quar. Jour., July,
1863; Contributions to Lithology, Part I, American Jour. Science)
March, 1864.

In view, then, of my theoiy of tlie derived and sedimentaiy
Origin of all eruptive rocks, what does Mr. Forbes mean when he
inquires whether I am aware of the immense masses " of volcanic

mmmmmm

rocks (trachytes) sc<attercd all over the face of the glohe, which
contain abundance of free quartz?'' If he will refer to my Contri-
butions to Lithology, just cited, he will find that I have insisted
upon the presence of quartz in trachytes, and, also, upon tile fact
that such trachytes pass into granites, from which they differ only
in structure (Amer. Jovr. Science [2] XXXVII, 260). The obvious
conclusion to be drawn from the presence of quai-tz in granites
and trachytes, is that neithei' during nor subsequent to crystallizti-
tion, have these rocks been subjected to a temperature sufficiently
elevated to alter the quaitz in the manner observed by Rose. In
the paper last cited, I have devoted two pages to an analysis of
the beautiful researches of Sorby on the microscopic structure
of crystals, about which Mr. Forbes talks, though evidently with-
out any conception of their geological beai-ing. Mr. Sorby, who
makes of the ctwities partially filled with watery solutions, which
occur in many crystals, thermometers which registered the tem-
perature at which these crystals were formed, concludes that the
quartz, mica, feldspar, and tin-stone of the Comish veins " were

deposited from water

holding various

salts and acids, at tem-

peratures varying from 200^' centigrade to a low red heat," about
340*^ ; while for some minerals from Vesuvius, which pre-
sent, besides cavities holding liquids, others filled with stoney
and glassy matters, he deduces a temperature of from 360*^ to 380*^,
and concludes them to have been formed "at a dull red heat,
under a pressure of several thousand feet of rock, when water,
containing a large quantity of alkaline salts in solution, was pres-
ent, along with melted rock and various gases and vapors. I
therefore think (he says) we must conclude provisionally, that at
a great depth from the surface, at the foci of volcanic activity;
liquid water is present along with the melted rocks, and that it
produces results which would not otherwise occur." (Quar. Jour.
Geol. Soc. XIV, 483.) One of these results, as is evident from the
above citation, is the reducing of rocky matters to a melted condi-
tion, at a dull red heat, a point to be borne in mind when Mr.
Sorby speaks in his paper of ifineousfumon in this connection. A
true igneous fusion of such matters, unthout wafer, would, as every
one knows, require a vastly higher temperature ; and I have else-
where, after Scheerer, described this softening of mineral matters
under the combined influences of water and heat, as an igneo-
aqueous fusion.

Mr. Sorby has, moreover, ailculated the temperature at which the
quartz crystals in the trachyte of the Ponza Islands, cited by Forbes,

were formed, and finds it to be 360 ®, they being, in fact, generat-
ed under like conditions with those of the quartz of granite vein?,
from which Mr. Sorby rightly concludes to a similarity of origin
between trachytes and granites. That both have crystallized at tem-
peratures not above dull redness, under great pressure, and in the
presence of water, is precisely what I have always maintained. When
it is remembered that copper, gold, and silver require for fusion,
from 1(X)()" to HOO'^, and (juartz a temperature of 'ISiW, it may not
be thought incorrect forme to designate 3G(r, the highest assigned
by Mr. 8orby for the crystallization of quartz, as a " comparatively
low temperfiture," to which expression, however, Mr. Forbes takes
exception. Mr. Sorby further concludes from his investigations of
crystalline metamorphic scliists, that they must have crystallized
at about the same temperature as the granites, atiording, in his
words, "a strong argument in fovor of the supposition that the
temperature concerned in the normal meiamorphism of gneissoid
rocks, was due to their having been at a sufficiently great dej^th
under superincumbent strata."

The reader may now judge how far the views of Mr. Sorby, whom
Mr. Forbes invokes, differ from my own on the subject of metamor-
phic rocks, of which I say in my lecture, as (juoted by Mr. Forbes,
that they have been formed from oi-dinary sedimentary strata,
" depressed so that they come within the action of the earth's central
heat," a proposition which our critic thinks "maybe disputed."
What theory he substitutes, he does not deign to inform us, but
proceeds to ask how I explain the depression of strata on the sur-
face of a globe with a solid centre. Both in my lecture and in the
papers already cited, I have taken pains to explain that the deeply
buried layers of sediment, together with the superficial and water -
impregnated portions of the solid nucleus, constitute a softened or
plastic zone, from which all plutonic and volcanic rocks proceed,
and which allows of the movements observed in the solid crust.
Is Mr. Forbes aAvare that geology affords many examples of depres-
sion of the earth's surface over great areas, permitting accumula-
tions of sediments, to the extent of 40, (XX) feet or more, followed
by elevation of the yielding crust and denudation to as great an
amount ?

I here take occasion to call attention to .an important considera-
tion in this connection deducible from Mr. Sorby's admirablt?
Bakerian lecture before the Royal Society, in 1863, on the Direct
Correlation of Mechanical and Chemical Forces, in which he shows
how chemical action is produced by mechanical force. Stating

il ^

from a consideration of the results of Bunsen and Hopkins that
thosft bodies which expand when fused have their point of fusion
raised by mechanical pressure, and from the discovery of Sir Wm.
Thompson that water, which contracts in melting, has, on the con-
trary, its melting point lowered by pressure, we may say that as
the solution of a solid hi a liquid is a kind of fusion, the same
general law will hold good, and that, for all those salts which con-
tract in dissolving (to which rule there are very few exceptions),
the solubility should be increased by pressure. This was abun-
dantly established by the experiments of Mr. Sorby. If now, we
suppose that the mineral compounds of the crystalline rocks, like
most salts, occupy a less bulk when dissolved that when in the
solid state, we can understand the greatly increased solvent power
of the water present in sediments submitted to a pressure equal to
many thousand feet of rock. Moreover, as suggested to me by
Sir William Logan, the diminution of solvent power of the liquid
as the pressure is removed, will help to explain the deposition of
mineral matters from watery solutions, which in their upward flow
tlii'ough fissures in the earth's crust, have given rise to mineral
veins.

But Mr. Forbes, after considering the conclusion of Sorby that
water has played an essential part in the crystallization and soften-
ing of rocks, which have been effected at temperatures not abcive
low redness, charges me with ''sensation" writing in asserting that
the plutonists claimed that igneous rocks were formed " entirely
by fire," and accuses me of injustice to the memories of Hutton,
Playfair, Hall, Humboldt and Von Buch, whose writings "show
that they never overlooked the all-important influence of water."
Now I mentioned none of these geologists in my lecture. As to
Hutton, to whom belongs, I believe, the idea of the metamorphic
origin of the crystalline schists, I have elsewhere written (Dublin
Quar. Jour. July, 1863),*' I accept in the widest sense the view of
Hutton and Boue that all the crystalline stratified rocks have been
produced by the alteration of mechanical and chemical sediments."
The question before us is, however, neither the views of Hutton
nor yet the origin of metamorphic rocks, but what both he and
modern plutonists hold with regard to the origin of granite, whose
derivation from metamorphosed sediments neither he nor they
admit. With regard to this point Mr. Forbes elegantly says " the
idea of dry fusion could only have originated in the brains of their
antagonists." Farther in a note to a paper on the Microscope in
Geology, in the Popular Science Eevieio for October, he says, with

equal good taste and truth, " the idea of a true dry f union in nature
exists only in the brains of the ultra-neptunist or the luke-warm
hydrothermalist," and asserts that in igneous action, the agency of
water was always recognized. He alludes to Poulett Scrope, who in
1824, put forth his views on the intervention of water in giving liqui-
dity to lavas ; but as Mr. Scrope himself tells us in his late paper
{Quar. Jour. Geol. S<j('. XII. 343,) his views were declared to be
unchemical, discredited and ridiculed ; nor was it till in 1847, when
Scheerer published his remarkable essay on the origin of granites,
(Bid. Geol. 8oc. Fr. [2] IV. 468,) that lithologists began to admit
that water had intervened in the generation of granite and other
eruptive rocks. But our readers shall judge what value is to be
attached to Mr. Forbes's assertions in this matter. After Scheerer" s
view of aqueo-igneous liquidity had been made known to the Geolo-
gical Society of France, Durocher, as the champion of the jilutonists,
maintained in opposition to it, the hypothesis already referred to
of a separation of the yet liquid globe into two layers, the lower
one heavier and basic, the upper lighter and acid, which by its soli-
dification gave rise to gi-anite. While he declared that " Scheerer'' s
new theory has for its principle the introduction of water in the
solidification of granitic rocks," Durocher conceived all the watei'
found in eruptive I'ocks to have been subsequently absorbed by
them, (Bill Sor. Geol. [2] IV. 1029, 1032.) Riviere, following a
second communication by Durocher on the same subject, declares,
"I think with Durocher, that water has flayed no part (ti'ajou^
aucun role) in the formation of granite,^'' and as to the rocks consi-
dered by Scheerer (granites etc.,) asserts ^^ the geological position
of these absolutely excludes the intervention^'' of neater, (Ibid. [2] VII.
287.) I might further quote Fournet, who in his G6ologie I.'ion-
yiaise, strongly maintains similar views to the above, and invokes
in favor of his purely igneous theory, the results and the
statements of Hutton and Hall, Lest, however, there should
be any mistake, and that the advocates of dry fusion, Durocher,
Riviere and Fournet, be, after all, ultra-neptunists, I shall
cite Elie de Beaumont, who in his classic essay on Volcanic Ema-
nations, etc., (published in 1847,) Bui. Geol. Soc. Fr. [2] IV. 1249,
has admirably discussed the question before us, giving the views
of Fournet and Durocher, the former of whom explains the liquid-
ity of granite by a surfusion of the quartz, which melts at 2800 ^
centigrade, but remains viscid at much lower temperatures on
cooling; while Durocher, on the contrary, imagines "a sort of fusi-
ble alloy" of the various elements, from which the feldspar and

m7'"\ crystallized. Rejecting these, which he designates as " pureb/
igneous surf imon,''^ he declares in favor of Scheerer's '■^altogether
novel idea,^' of a condition of quasi-fluidity at a low red heat, due
to the intervention of watei*, and asserts that "the hypothesis of a
primitive state of simple igneous J'lmou of granite, notwithstanding
the evidences brought forward in its favor, is no longer justified,"
(loccit. p.p. 1305, 1.311.) It is in the face of records like these, and
despite the energetic protest of plutonists against the possibility of
the intervention of water, and in favor of a dry fusion or a simply
igneous fusion of the elements of granite, that Mr. Forbes has the
hardihood to assert that tlie intervention of water in igneous agency
" was always recognized by the plutonist."

But I have not done with Mr. Forbes until he shall have shown
how, with his owti theory of tlie earth, he explains the intervention
of \Vater in all igneous rocks, which, as he declares, are outbursts
from the still fluid interior of our globe. How did the water find its
way there, since, according to him, far above the already solidified
crust, this element at first formed a vaporous layer, separated from
the earth by a stratum of volatile chlorids and another of carbonic
acid? In virtue of what law did this water, after its precipitation, dif-
fuse itself throughout the various layers of the liquid mass which
still fills the centre of the earth, so as to be pi-esent in every
eruptive rock coming up from that great reservoir ? For my part,
I am inclined to say with Riviere, tliat the geological position of
such mattersmust "absolutely exclude the intervention of water,"
and until Mr. Forbes, or some other plutonist, shall have given a
plausible hypothesis to explain the fact, which he admits, of the
universal diffusion of water in igneous rocks, I prefer my own
theory of their origin, namely : that the anhydrous and incandes-
cent nucleus of the globe is solid, and, except in its outer portions,
takes no part in volcanic or plutonic phenomena, which have their
origin entirely in the stratified sedimentary deposits, and in those
superficial portions of the nucleus which were necessarily permeat-
ed, during their partial cooling and consequent contraction, by the
superincumbent waters.

One word in conclusion ; Mr. Forbes, who prides himself on his
great opportunities of travel, and on his geological studies in var-
ious regions, discourteously taunts me with my own more limited
field of investigation. Let me tell him in reply, that if the three
papers which he published in October last, show any one thing
more clearly thsm his unfamiliarity with geological literature, it is

hia ignorance of the facts of geognosy, and that he involuntarily
recalls to mind the wise saying of Thomas k Kempis, passed into a
proverb among churchmen : « those who make many pilgrimages
rarely become saints."

Montreal, December, 1867.

ON THE CHEMICAL GEOLOGY OF MR. DAVID FORBES:

BY T. STERRY HUNT, F.R.S.

In the Chemical News of October 4th, 1867, there appears a paper
purporting to be a criticism of some views on the chemistry of
the primeval earth, put forward by me in a lecture delivered before
the Royal Institution of Great Britain, on the 31st of May last, and
published in the proceedings of that Institution, as well as in the
Chemical News of June 27th, and the Heme des Cours Scientijiques,
of October 19th, as also in Les Mondes and Cosmos. The object of
my present communication will be to notice briefly some of the
criticisms of Mr. Forbes. The readers of my lecture are aware
that I assumed as my starting point the hypothesis, now generally
accepted, of the origin of our earth, and of all planetary and stel-
lar worlds, by a process of condensation and cooling from a nebul-
ous or a gaseous matter, so intensely heated as to be luminous, and
to contain, at the same time, in a free or dissociated condition, the
various chemical elements. The first objection of Mr. Forbes, is
that I do not explain the origin of this intensely heated condition:
a consideration entirely beyond the scope of my lecture, but e -
tablished by the spectroscope, and to be accepted as an ultimate
fact, the secret of which, like that of the origin of matter itscir,
rests with the great first cause.

In discussing the laws which j^resided over the cooling of our
own globe, I gave several reasons which have led modern inves-
tigators to reject the old theory of a liquid centre covered by a
thin crust of congealed rock. I alluded briefly to the mathema-
tical deductions of the late Wm. Hopkins from the phenomena of
precession and nutation, — those of Ai-chdeacon Pratt on the feeble
resistance which would be offered by a crust of the thickness gen-
erally admitted by the old school, to the crushing weight of masses
like the Ilimmalayah Mountains, — and the conclusions of Thomp-
son as to the rigidity of the earth, deduced from the theory of
thb tides, as so many concurrent arguments in favor of a crust at
least many hundred miles in thickness, if not. of a globe entirely
solid. Proceeding, thence, to consider the conditions of cooling
liresented by the fused and oxydized mass of the globe, I assert-
ed that the analogies offered by most of the bodies forming the
earth's crust, which yield comi^ounds considerably denser when
solidified than when in their fused condition, lead us to conclude
that the solidification of the globe must have begun from the
centre. In fact, the numerous and detailed experiments of Charles
Deville, {Covipies Rendns, XX. 1453) and those of Delesse, {Bull.
Soc. Geol. dti Fr. [2] IV. 1380.) not to mention the earlier ones of
Bischof, unite to show that the density of fused rocks is much less
than that of the ci-ystalline products resulting from their slow
cooling, so that, as Saemann has justly observed, we are forced to
conclude that the crystalline stoney masses formed at the surface
of a li(}uid globe must sink towards the centre (Ibid. Feb. 4. 186i).
To this conclusion Mr. Forbes objects that, in the cooling of sulphur
or metals from fusion, a crust forms at the surface before the in-
terior is solidified; he should consider that the conditions in a
small crucible, placed in a cold atmosphere, where cooling is rapid,
and the crust is sujiported by adhesion at the edges, are vastly dif-
ferent from what would obtain in a world-wide bath, cooling with
great slowness beneath an intensely heated atmosphere. In such
a case, as the crystallino silicates known to us are, according to
numerous expeiimen.s, from one-seventh to one-sixteenth denser
than tlie same materials in a fused condition, it would lerjuire a
suspension of the laws of gravity to counteract the inevitable
tentlency of tlie heavier solids formed at the surface to sink in
tlie fusecl mass, in which they would subside as natvu-ally as the
crystals which form at the surface of an evaporatmg basin of brine.
The analogy holds good, since the crystals formed at the surface,
whether by evaporation or by cooling obey the laws of gravity.

The freezing over of the surface of such a mass would be as
unnatural as the freezing of a lake of water from the bottom.

Mr. Forbes next comments niton my allusion to the experiments
of Hopkins on the effect of pressure in elevating the melting
points of such bodies as contract in cooling, and says that I appeal
to these as conclusive proof that the melting points of bodies do
become (ad infinitum) elevated in proportion to the pressure. In
fact, I said nothing of the sort, but insisted that the researches of
Hopkins "are to be considered in this connection." If Mr.
T'orbes had taken some pains to inquire into the question, he
would learn that these experiments of Hopkins, and others (by W,
Thompson on the effect of pressure in reducing the melting point
of ice) were suggested by a remarkable essay by James Thompson
(Trans. Roy. Soc. Edin. XVI, part 5). In this it was shown that the
fusing point of ice, which contracts in melting, must necessarily
be reduced by pressure ; while, as Sir Wm. Thompson showed,
the reverse effect was to be expected for all solids which expand
in melting (L. E. and D. Phil. Mag. [3] xxxvii. 12.5). The results
of Hopkins thus come under a general physical law. Mr. Forbes
will find a simj^le and intelligible statement of the principle laid
down by Thompson, and Hopkins's argument therefrom for the
solidity of the interior of the globe, in the fourth of Dr. Tyndal's
admir.able lectures on Heat, delivered before the Royal Institu"
tion. See also Mr. Sorby's Bakerian lecture for 1863. As to Mr.
Forbes's suggestion of denser matters towards the earth's centre,
I have said the same thing in my lectm-e.

Mr. Forbes next proceeds, in his own words, to submit my views
of the chemical changes which took place at the surface of the
globe, to "careful scrutiny," in order to determine whether
" they are sound and likely to meet with acceptance in the che
mical world." Of the critic's fitness for his self-imposed task the
reader shall judge. The first thing to be determined in the cool-
ing of an intensely heated vaporous mass is the nature of the che-
mical compounds which would be formed among the dissociated
elements. As I have stated in my lecture, the combinations stable
at the elevated temperature then prevailing, would be first formed.
The affinities of oxygen are such, that under such conditions, an
excess of this element being present, instead of sulphids of the
heavy metals, as imagined by Mr. Forbes, oxyds and sulphurous
acid would be produced in virtue of affinities known to every che-
mist and metallurgist. So with regard to chlorine, the production
of alkaline chlorids in such conditions is inconceivable, since in

the conjoined presence of oxygen, hydrogen and silica, an alka-
line silicate and hydrochloric acid would necessarily result. Even
if, as Mr. Forbes supposes, chlorid of sodium were to be formed in
the heated atmosphere, it would be precipitated into an intensely
heated bath of fused silicates, covered by an atmosphere charged
with aqueous vapor, or with mingled hydrogen and oxygen, and
would immediately undergo the same decomposition that takes
place when the vapors of common salt are diffused through the
heated atmosphere of a potter's kiln, or, as in Mr. Gossage's new
soda-process, are passed with steam over red-hot flints. In both
cases silicates of soda are formed, with separation of hydrochloric
acid. These considerations lead to the conclusion that, after all
the more fixed elements were precipitated, the whole of the chlo-
rine would remain as hydrochloric acid, and the whole of the sul-
phur as sulphurous acid, together with a larg'^ proportion of oxy-
gen, since we find sulphates and not sulphites in the sea-waters.
To this constitution of the still intensely heated atmosphere, Mr.
Forbes objects, and inquires whether it is "at all probable, even
if possible, that an excess of oxygen could exist along with the
vast amount of sulphurous acid." He farther adds that "the
improbability of such an atmosphere containing a mixture of
hydrochloric and sulphurous acids, may be inferred from Diunas's
researches ; that chemist having long ago shown that these two
gases, when mixed together, react and mutually decompose each
other, with the formation of watei*, chlorine and sulphur." Mr.
Forbes thinks he has hit upon two objections to the existence of
a heated atmosphere holding, as I have endeavored to show,
besides nitrogen, oxygen and watery vapor, sulphurous and hydro-
chloric acids. He has evidently a vague notion that sulphurous
acid and oxygen have an attinity for each other, and ought to
form together sulphuric acid. So they do unite slowly at proper
temperatures, in the presence of water, being converted into oil
of vitriol, and it was doubtless in this way, as I have elsewhere
shown, that tlie sulphur was eventually brought down from the
atmosphere, and formed the sulphates of the sea. But every che-
mist is aware that at higher temperatures oil of vitriol is resolved
into water, sulphurous acid and oxygen gases, and that this reac-
tion is made use of as an economical process for the preparation
of oxygen on a large scale, the sulphurous acid being removed V)y
absorption *rom the cooled gases. As regards his second point,
Mr. Forbes, who cites Dumas (Traite i. 146) has been mislead by
quoting at second-hand, apparently from the English edition of

Gmelin (ii. 321). Dumixs states that in solution sulphurous acid
and hydrochloric acid undergo no change; but, *4n a dry state,
on the contrary, they are rapidly decomposed, at least in operat-
ing over mercury." It may be true that as Gmolin states, water,
chlorine and sulphur result, but such is not the assertion of Dumas.
The point, however, is immaterial, since as Dumas and Gmelin
state, and as every chemist knows, the two gases remain unaltered
in the presence of water, even if in the form of vapor. Indeed, it
happens, unfortunately for both of Mr. Forbes's objections, that
large quantities of precisely such an atmosphere as he supposes to
be impossible, are disengaged from numerous volcanic vents, as
he will find by referring to the researches of Charles Deville and
Leblanc. (Ann. de Ch. et Phys. [3] LIT. pp. 5-63). Among other
examples described by these chemists, a fumcrolle of Vesuvius
yielded in June, 1856, a mixture of highly heated steam, hydro-
chloric acid and air, the latter containing in 100 parts oxygeo 18.7,
sulphurous acid 2.6, the remainder being nitrogen ; while the
acids of the steam and air together yielded for one part of sulphur-
ous acid about five parts of hydrochloric acid. Traces of sul^jhuric
acid, due to the slow union of the sulphurous acid and oxygen, were
found in the water condensed from tliis fumerolle. Volcanos, as
I have elsewhere stated, rejiroduce, on a limited scale, the condi-
tions of the primeval earth, not only in their solid but in their
gaseous products.

Mr. Forbes proceeds to comment upon my illustration of the
condition of the primitive globe from a supposed reaction of tlie
present air, sea and land under the influence of intense heat. He
suggests that the cju-bonaceous matters would convert into sul-
phids the mineral sulphates. Here, as before, he ignores the
intervention of water and silicious matters, which would cause the
sulphur to escape in the form of sulphuretted hydrogen, (which is
doubtless evolvetl from modern volcanos by a similar reaction),
and this at an elevated temperature, would at once be burned to
sulphurous acid and water. He descends to trifling when he objects
that by the eftect of heat upon the present surface of the globe,
the water of the sea would be first evaporated, and then the chlo-
rid of sodium sublimed in its'turn. It was made clear to every
reader, that I never intended by this illustration to represent the
process of nature ; moreover, I said, "j/' the elements were made to
react upon each other,^^ which would not be the case if they were
successively removed by evaporation beyond the sphere of reac-
iions.

Here I cannot resist the temptation of giving my readers a
choice specimen of Mr. Forbes's chemistry, which he has em.
bodied, with many other sm-prising tilings, in a further criticism of
my lecture, which appears in the Geological Magazine for October,
but has, for some unknown reason, withheld from the readers
of the Chemical News. Proceeding to give his own notions of the
chemistry of the primitive globe, Mr. F. supposes that imme-
diately above the " solidified crust," there existed a zone com.
posed chiefly of chlorid of sodium; "above this, a stratum of
carbonic acid, and then of water in the form of steam, whilst the
oxygen and nitrogen would be elevated still higher;" and, proba-
bly, also, in Mr. F.'s imagination, separated according to their
densities. In explanation of this order, he tells us, in a note, that
the zone of carbonic acid gas would be heavier than that of steam,
and should therefore come below it ; he even gives their res-
pective weights, but he forgets that oxygen and nitrogen are
also both heavier than steam, and should be found below, and not
above, this zone of watery vapor. In fact, as is Wfll known, the
specific gravity of oxygen being 1.109, and nitrogen, 0.970, that of
atmospheric air is l.(XX) ; while carbonic acid gas is 1.525, and that
of watery vapor, 0.G24. But, apart from this absurd mistake, what
shall we say of the man who disphiys an utter ignorance of the
laws which govern the diffusion of gases and vaj^ors ? Will Mr,
Forbes explain why it happens that in our present atmosphere,
these same elements, namely, oxygen, nitrogen, carbonic acid
gas, and watery vapour, are commingled, instead of being, as he
would have them, arranged in separate zones ?

Mr. F.'s mode of explaining the saltness of the sea must fall to
the ground, unless he succeeds in showing how, despite well
known chemical affinities, the requisite amount of chlorid of
sodium could be formed and preserved under the conditions which
I have discussed above, so that, as he supposes, it was ready to be
dissolved by the first waters precipitated on the surface. When
he has satisfactorily established this part of his theory, he will,
perhaps, tell us how sulphates found their way into the sea, if, as
he asserts, all the sulphur was at first separated in the form of
dense metallic sulphids, which sank at once, " and remained in
the interior of the earth, protected from oxydizing action?" Mr.
F. may have data unknown to the world, for estimating the total
amount of sulphur in the globe; but when he tells us that it
would be sufficient to convert all the soda of the sea to sulphate,
he reasons as if the amount of bases in nature were limited, for-

getting that the earth's crust contained more than enough of
alkaUes, lime, and magnesia, to saturate the acids of the primeval
atmosphere, and, moreover, that the whole of the sulphur, sul-
phates, and sulphids of the earth's crust, have, to judge from all
analogy, been derived from the soluble sulphates of the ocean.

Mr. F. next proceeds to inquire why the sea contains so much
sodium, and so little potassium ? If he will study the question,
as he may do in my Coniributions to the Chemistry of Natural
Waters (Amer. Jour. Sci. [2] xxxix, 176; xl, 43, 193.),, he will
learn that at an early period the salts of calcium and magnesium
greatly predominated over those of the alkalies in the ocean
waters, precisely as they must have done in the crust of the
primitive earth. It is by subsequent subserial decomposition
that have been liberated the alkalies, which, in the form of car-
bonates, have decomposed the salts of the primitive sea, and sub-
stituted sodium for calcium, for it is well known that natural
alkaline waters convey to the sea chiefly soda, and comparatively
little potash, which is retained by argillaceous sediments. More-
over, the potash which does find its way to the sea, is constantly
withdrawn in the form of glauconite, and also by the agency of
fucoids, which, as Forchammer has shown, fix great amounts of
potash, and, subsequently, by their decay in the ooze, restore it
to the earth.

Mr. Forbes next expresses surprise that I find the origin of all
carbonate of lime (except that from the subaerial decomposition
of primitive calcareous silicates) in the reaction of carbonate of
soda on the lime-salts of sea-water, since, according to him, the
results of the careful study of limestone rocks by geologists, pale-
ontologists and microscopists have shown these rocks to be ^*the
result of organic actioti.^' And, moreover, that neither chemists
nor zoologists will accept my assertion that animals can only appro-
priate the carbonate of lime which they find ready formed, but " will
consider these animals ciipable of utilizing the other lime-salts in
the sea." If we admit the power of the lower animals to decom-
pose chlorid of calcium or sulphate of lime, as would appear from
the acid liquid said to be found in some of them, will Mr. Forbes tell
us what becomes of this at the death of these animals, and how the
acid is to be disposed of ? If the thousands of feet of limestone
strata, consisting in large part of organic remains, have been
derived from the decomposition of the sulphate or chlorid of cal-
cium of the sea by any other process than by that which I have
indicated, namely, the inteivention of alkaline carbonates, will

f^i^^mmmimm

Mr. Forbes kindly inform us what has become of the vast amount
of hydrochloric acid equivalent to all this carbonate of lime ?

As to the origin of dolomites, Mr. Forbes will do well to read my
paper in the Amei: Jour. Science, for July, 1866 ( [2] XLII, 49). In
this, at § 112, he will see that apart from the formation of stratified
sedimentary dolomites, I insist upon the frequent occurrence of
dolomite as a mineral oi' secondary deposition, lining drusy cavi-
ties, filling veins, and even the moulds of fossil shells. To such
cases, the observations of Sorby and of Ilarkness may probably be
referred ; the microscopical investigations of the former, as given
by him in the British Association Report for 1856, are like all the
other works of that excellent observer, doubtless entitled to the
highest credit. No one, however, who has carefully studied, as I
have done, the distribution and association of the great beds of
dolomite which occur in the Lower Silurian rocks of Canada and
New England, can, for a moment, admit that they are the products
of subsequent alteration. Repeated alternations of pure blue lime-
stones with reddish ferruginous dolomites, interrupted beds and
patches of these enclosed in the former, the line of demarcation
sharply drawn, and finally conglomerates in which pu^e limestone
pebbles are enclosed in beds of dolomite, all of which may be stu-
died near Quebec, are evidences incontrovertible against the
theory of dolomitization of pure limestones, and in favor of the
deposition of dolomites as magnesian sediments.

Mr. Forbes insinuates that I am unaware of the various specula-
tions and theories which have been put forward to explain the
supposed origin of dolomites by alteration. Although the stratigra-
phical relations of dolomites, as described above, set aside entirely
this hypothesis of its formation, at least in the great majority of
Mr. Forbes will find that the observations and speculations of

cases,

Haidinger, Von Morlot, Marignac, and others on this subject have
been discussed and made the subject of multiplied experiments
by me in a memoir published in 1859, {Amer. Jour. Sci, [2] XXVIII.
170, 365) and farther in the paper quoted above ; and that I have
shown that the reaction ofthe sulphate of magnesia on carbonate of
lime, to wliich he refers, does not give rise to dolomite, but to an
admixture of the carbonates of lime and magnesia.

Some of the results of my prolonged study of certain salts of lime
and magnesia, which are for the most part set forth in the papers
just referred to, were, says Mr. Forbes, by me considered worthy of
being presented to the French Academy of Sciences (Comp/e* Rendus,
April 22, 1867,) .although he declares the reactions there described

d -

to have been for twenty-five years in general application on a large
scale in Great Britain, for the manufacture of magnesian salts
Here it becomes difficult to admit the plea of ignorance which sug-
gests itself for most of Mr. Forbes's previous statements. I have in
the note to the French Academy above referred to, pointed out the
following as facts discovered by my investigations of the salts
of lime and magnesia : 1st. That bi-carbonate of lime, at ordinary
temperatures, decomposes solutions of sulphate of soda and sul
phate of magnesia, with formation of sulphate of lime and bi-car
bonates. 2nd. That from mingled solutions of sulphate of mag
nesia and bi-carbonate of lime, there separates, by evaporation, crys
stalline gypsum, and subsequently a hydrous carbonate of mag
nesia ; the bi-carbonate of this base being, as is well known, very
much more soluble than the sulphate or the bi-carbonate of lime.
3rd. That this separation of gypsum is favored and rendered more
Complete by an atmosphere impregnated with carbonic acid gas,
and 4th. That mixtures, in due proportions, of precipitated carbo-
nate of lime and hydrous carbonate of magnesia, when gently heat-
ed under pressure, and in the presence of water, unite to form the
anhydrous double carbonate, dolomite. These are the reactions
which I described to the French Academy as new, and I demand
Mr. Forbes to make good his assertion to the contrary, or to show
that any one of them has been employed for the last twenty -five years
in the manufacture of magnesian salts.

Montreal, December, 1867.