f2>e4 . 
chemical element into another, or give rise to products having 
at all times a definite chemical and mineralogical constitution, 
out of the incongruous materials likely to be met with” in the 
crust of our globe. 
* Our knowledge of the mineral characters of that crust does 
_ not admit the supposition that the substance of the rocks occur- 
ring in so many different parts of the world could in all or 
in any but solitary in-tances when fused by mere heat afford 
products identical with those of known volcanoes. 
*€Volcanic products, no matter from what part of the world 
~ derived, are identical in chemical or mineralogical constitution ; 
a result which indicates that they must be derived from some one 
common source, and not mere local accidents, as Mr, Mallet’s 
hypothesis would require us to assume. 
“For these and other reasons [none of which are suggested] 
itdoes not seem probable that this Ayfothesis will receive the 
adherence of either chemist, mineralogist, or geologist.” The 
italics are mine. 
Now I cannot help remarking that Mr. Forbes shows his 
very slender acquaintance with the yast subject he so 
jejunely disposes of, by the very language he employs ; force 
cannot be converted into heat, equivalent or otherwise ; work, 
z.é. pressure producing motion, is transformable into heat, and 
every other known form of energy. But passing this as well as 
the reiterated confusion between hypothesis and theory, I ask, is 
it a fact as stated, that volcanic products whencesoever derived, 
in time and in space over the whole globe, are zdentical in chemical 
or mineralogical constitution. I affirm unhesitatingly that it is 
not a fact, and I appeal for confirmation of my denial to 
every authoritative work on the subject, and to every well- 
informed mineralogical chemist. 
Are the ancient basalts and trachytes identical with the modern 
ones, or with each other in different localities? Are the modern 
lavas of extinct or active volcanoes all over the world, or even 
at closely adjacent places, all identical? Are the highly liquid 
lavas of Otaheite, producing ‘‘ Pele’s hair,” the same with the 
terrane lavas of Etna? Are the trachytes of Auvergne—the 
Pierre de Volvie so well known to French engineers, the same as 
those of Pozzuoli and of the Rhine? Are the products of the 
same volcanic basin ever identical—say the pumices and ob- 
sidians of Pouza, Ischia, and Lipari—with the innumerable 
varieties of lava of the same localities, and of the phlegrzan 
fields and of Sicily? Are even the lavas of the same cone and 
during the same eruption always identical? Palmieri in the very 
report Mr. Forbes reviews, says (p. 105), ‘‘ The guadttative analysis 
of the (Vesuvian) lavas always presents the same elements,” with 
certain exceptions ; ‘‘but with respect to guan#ifative analysis, 
two specimens of the same lava have their constituents in 
different proportion.” Nay more, are eyen the crystallised 
minerals of definite chemical constitution, as segregated from 
the lava pastes or glasses, zd@entical all over the world, or even 
for any one cone, or often for any one eruption? No, there is 
just that general similarity in the constitution of volcanic pro- 
ducts that we should expect to result from the heating more or 
less, or the fusion together of the “incongruous” beds, siliceous, 
aluminous, magnesian, calcarious, mixed more or less with 
metallic oxides, or other compounds, and often with carbon, 
boron, and other elements all variously superposed or mixed, 
which constitute the known crust of our globe, along with most 
probably the materials of crystalline or other rocks below, the 
nature of which we can but guess at. There is just the same 
general similarity that is seen in the slags of all metallurgic 
furnaces, which fuse very similar materials to the volcano, but - 
- with a preponderance of some metal also. 
Are the slags of 
the same iron blast furnace édentical even for any two tappings, 
though the working and charge is apparently the same? No, 
and for very obvious reasons. Are even the crystallised minerals 
that segregate from these slags, from the same furnace assumed, 
worked in the same way, always identical? 
If Mr. Forbes will study Von Waltershausen’s early and able 
work on Lavas, one scarcely known in this country, Zirkel’s 
**Petrographie,” Senft’s “Kristallmischen Felsgemengtheile,” 
and above all Blum’s ‘* Hancbuch der Lithologie,” amongst many 
others he will soon see how very baseless is the supposed fact on 
which he so confidently relies for his objection to my origin of 
a 
volcanic heat. 
But let us for a moment assume that it were a fact that all the 
volcanic products all over the world, and for all geologic periods, 
were ‘‘identical in chemical and mineralogical constitution,” 
how would that form any releyant objections to the thermo- 
Ss NATURE 
383 
dynamic origination which I have assigned to volcanic heat, 
Or how would it help the old notion of a very thin crust and 
a universal molten ocean beneath, or the exploded one, that 
chemical action produces the heat, and the heat produces the 
chemical action. 
Whatever be the origin assigned to the heat, it is within or 
below the heterogeneous solid crust of ro to 40 miles thick, 
which we are acquainted with. More or less of that hetero- 
geneous crust must be melted up, along with the material assumed 
everywhere the same of the molten ocean coming up through it 
from beneath. 
It is proveable on merely hydrostatic grounds that the mass of 
such a molten ocean, if of materials such as are found in onr 
earth’s crust, could nut be everywhere and in all latitudes identi- 
cal in construction ; but were it so, it must get contaminated and 
modified in passing through and melting the ‘‘ incongruous” 
‘ducts of the crust bringing it to the surface. 
On the other hand absolute identity everywhere in the volcanic 
products, did it exist, could prove nothing in favour of a uni- 
versal ocean of ready-made lava as the source or origin of volcanic 
heat ; but only that whatever might be the origin of that heat it 
was so circumstanced as toact on materials every where the same, 
and that these reached our surface without any action or mixture 
with the ‘‘ incongruous ” crust through which the molien matter 
came. There is just the same room for ‘local accident” in 
one case as in the other. A reviewer should at least be sure of 
his facts before he brings them into hostile array. 
But again, what are the grounds for the assumption that 
according to my views, volcanic products of whatever sort 
are ‘‘the result of fusion by mere heat.” I point out a true 
cosmical and thermo-dynamic origin for the heat itself, but 
under the actual conditions of volcanic foci and ducts, chemical 
actions must take place, as a consequence of the heat, and to- 
gether vary the results of the reactions of aJl the materials pre- 
sent in fusibility, in aggregation, in their solid, liquid, or gaseous 
states, in their molecular conditions and in their chemical and 
crystallogenic combinations. This objection as littleapplies to 
anything I have written, as the irrelevant suggestion, that the 
transformation of energy ‘‘ cannot transmute one chemical ele- 
ment into another.” 
I believe this disposes of whatever is tangible or worth remark 
in Mr. Forbes’ strictures. 
He ends, however, in a manner unusual I should think for an 
unbiassed reviewer, by uttering a sweeping prophecy, ‘‘ for the 
reasons given [and above repeated], and others not brought 
forward, it is not probable that this hypothesis [z.e, my theory of 
volcanic energy] will receive the adherence of either chemist, 
mineralogist, or geologist.”” Prophecies, especially as to matters 
of science, are dangerous things, and the prophets would do well 
to rule by Swift’s advice, as to utterances of another class, and 
never record one that can be falsified within a short time. It so 
happens that I am able already to explode Mr. Forbes’s. Writing 
to me under date of Dec. 24 last (1872), Dr. Haughton, Professor 
of Geology of the University of Dublin, says—‘‘I gave two lec- 
tures during the Jast term (Michaelmas) which were attended by 
many of the fellows, in which I developed your theory of volcanoes 
and gave you full credit. The whole system hangs well together 
and must make progress.” Prof. Dana (in noticing this same 
book which Mr. Forbes so uncompromisingly condemns), as 
editor of the American Fournal of Science, for the month of 
February, 1873, at p. 151, says: ‘* His paper is the most im- 
portant contribution to this department of geological dynamics 
that has ever been brought forward, and the work above-men- 
tioned [z.e. Trans, of Palmieri] is by his share of it more than 
doubled in value.’ In a letter to me, Feb. 11, 1873, Prof. Dana 
says: ‘* Your views throw great light on a hitherto mysterious 
department of geological science, and I have no doubt that they 
will speedily gain general acceptance.” 
I could add like expressions from some others, Now both 
Haughton and Dana are at once chemists, mineralogists, and 
geologists. They are both, also, sound physicists and mathema- 
ticians. So this prophecy is already falsified, and Iam consoled 
with the notion that my theory of the nature and origin of yol- 
canic energy may survive the unreseryed condemnation to which 
Mr. Forbes has sentenced it, on the grounds that I have above 
examined, and without his ever having had access to the paper 
itself criticised by him. I might refute, too, some criticism on 
the book itself, which I cannot avoid calling unfair, and also not 
founded on fact. It is not true, for example, that the first forty- 
six pages of my introductory sketch “are but an abstract of my 
