286 
are mere local phenomena, each one springing from its own 
comparatively small reservoir of molten matter, supposed to have 
originated from the softening or fusion of rocks pre-existing on 
the spot at some depth below the surface. To me, however, 
this hypothesis appears altogether untenable when it is remem- 
bered, amongst other objections which Ihave elsewhere considered, 
that volcanic rocks are encountered in all parts of our globe, 
often continuous or nearly so, over immense areas, and that all 
these rocks, without reference to the part of the world in which 
they occur, are invariably alike in character to one another.” 
Volcanic rocks may be classified under two heads, viz., the 
dark-coloured, more dense ; and the less heavy, light-coloured 
lavas, termed, respectively, the basic or pyroxenic, and the acid 
or trachytic lavas. Both these varieties may proceed from the 
same volcanic vent in succession—for instance, in Vesuvius, 
where the mineral matter which buried Pompeii is trachytic, but 
the later lavas are generally pyroxenic in character. This also 
was the case in the recent eruption of Santorin, as reported 
upon by the Austrian Scientific Commission. 
The examination of volcanic products, no matter how distant 
the volcanoes may be from one another from which they are 
taken, prove them to be altogether identical in general, mineral, 
and chemical constitution. 
Taking all these and other data into due consideration, I 
cannot arrive at any other conclusion than that all volcanoes are 
connected-with one another in depth, and having one common 
source, not necessarily situated at any enormous depth below the 
surface, but in which the molten matter—whilst always containing 
certain general characters—has undergone considerable modifica- 
tionsin composition, mineralogicaland chemical, from time to time 
in the world’s history; for under the term volcanic rocks, I 
would here include all eruptive rocks without exception, whether 
called granites, syenites, porphyrites, basalts, or lavas, all of 
which I regard as but so many members of one series, or simply as 
the products of the volcanic action of different geological epochs. 
So much for the molten products of volcanoes. Now a few 
words on their gasiform emanations, which consist in greater 
part of the vapour of water, ze. steam, along with volatile 
chlorides, hydrochloric and sulphurous acids, nitrogen and 
sulphuretted hydrogen gases. The sulphur, seen to be sublimed 
in so large quantities, is probably derived from the mutual re- 
actions of the sulphurous acid and sulphurated hydrogen gases, 
as they come into contact with one another. ; 
Now if it be true that we have a vast accumulation of molten 
matter at a certain depth below the surface, which observation 
further informs us must, in major part, consist of the silicates 
and sulphides of the metallic elements, then, in my opinion, 
at least, it only requires the assumption that water from the sea 
should, by some means or other, find its way down into such a 
reservoir, to account for all the phenomena of volcanoes, both 
mechanical as well as chemical. The greater part of the water 
so introduced would be at once converted into steam, which, in 
its turn, would become still further expanded by a heat so great 
as that of molten lava, and would develope an enormous power. 
Calculations have been made which show that water, even 
when treated to a much less temperature, would exert an 
‘ejection force,” as it has been termed, even exceeding that 
developed in eruptions of the highest voleanoes known. Another 
portion of the water with the air carried down along with it, 
acting upon the highly heated sulphides, would become de- 
composed, and furnish the sulphuretted hydrogen, sulphurous 
acid, and nitrogen gases given off, whilst the common salt in the 
sea water, by its action on the hot silicates in presence of steam, 
would eliminate hydrochloric acid, and account for the appear- 
ances of it, as well as of the volatile chlorides found in volcanic 
fumes. If we accept this explanation. the chemical reactions 
would be but the effects and not the cause of volcanic phenomena. 
The destructive effects attendant on volcanic convulsions are 
of two different characters, viz., those arising from the earth- 
quakes which accompany and, as a rule, precede outbreaks ; 
and those caused by the products ejected from the volcano itself. 
The connection of earthquakes with volcanoes has been noted 
from the oldest times ; the earthquakes which commenced A.D. 
63, were but the efforts made by Vesuvius to relieve itself, 
which culminated in the great eruption of 79; the same was the 
case in Mexico with Jorillo in 1759, and with the great earth- 
quake of 1834 in Chili, which ended in the outbreaks of Osorno 
and three other volcanoes of the Andes ; and lastly, in 1868, the 
terrible earthquake which visited the coast of Peru and totally 
dlestroyed the cities of Arica and Iquique, was followed by the 
NATURE 
[Aug. 4, 1870 
eruption of Isluga, which, according to the latest news, still 
continues. There seems little reason to doubt that all earth- 
quakes are of purely volcanic origin, and that volcanoes them- 
selves may be regarded as so many safety-valves for blowing off 
the surplus steam, gases, and molten products from our great 
internal boiler ; for, as a rule, it has been observed that earth- 
quakes either cease altogether or diminish greatly in violence 
as soon as a neighbouring volcano has cleared its throat. 
Although I have resided several years in what are called 
earthquake countries, and have experienced numerous and severe 
shocks, amongst others those which resulted in the total destruc- 
tion of the cities of Copiapo and Mendoza, on which latter occa- 
sion some 20,000 inhabitants perished in the ruins, it seems to 
me quite impossible to convey in words anything like a true 
picture of such a dreadful catastrophe ; the feeble shocks occa- 
sionally felt in England cannot give you even the remotest idea 
of what a severe earthquake is in reality, for not only are cities 
destroyed and whole villages swallowed up in an instant, as in 
the case of Arqure during the eruption of Mount Ararat in 1840, 
but when situated on the coast, even when they have withstood 
the shock itself, they may be entirely swept away by the great 
sea wave which follows close upon it, as happened with the 
cities of Arica and Iquique, in Peru, little more than a year ago. 
Equally terrible is the destruction caused by the showers of ashes 
and torrents of molten rock, as in the well-known instances of 
Pompeii, Herculaneum, and others, too numerous to mention. 
The study of volcanic phenomena presents a wide and in- 
teresting field for exploration, for as yet our knowledge of the 
subject is lamentably defective. To follow it up, however, the 
student should work out a path for himself, taking advantage 
of every new means of research placed in his hands by the 
advance made hy the collateral sciences, and steering clear of 
all schools or preconceived notions. Schools in science are 
what parties are in politics; the ‘‘follow my leader” style will 
not do in this age, for it does not permit of that perfect inde- 
pendence of thought absolutely requisite to ensure success in the 
pursuit of science. The study of science is the search after 
truth, but in its study the persevering and conscientious worker, 
although sure to attain good results in the end, must always bear 
in mind that his results, even when proved to be ¢vzths, are still 
only fragments of the whole truth, and that he therefore should 
guard himself against oyerrating their value, 7.¢. the extent of 
their application, since this can only be correctly estimated when 
these fragments have been found to fit accurately into their true 
place in the grand plan of nature. D. FORBES 
SCIENTIFIC SERIALS 
Tue Journal of Botany for July commences with a shortaccount 
by Dr. D. Moore on a form of Saé/ix arbuscula in Ireland, which 
inclines rather towards S. yzyrsinites. Dr. Seemann proceeds with his 
“¢ Revision of the Natural Order Bigwoniacee,” and Mr. Worth- 
ington Smith with his valuable ‘‘Clavis Agaricinorum,” these 
three articles completing the portion of the paper devoted to 
original articles, which we regret to see reduced to so small a 
space. Then follow the second part of Dr. Braithwaite’s “‘Recent 
Additions to our Moss Flora,” and appreciative reviews of Dr. 
Hooker’s ‘* Students’ Flora,” and Prof. Babington’s ‘‘ Flora of 
Iceland.” 
THE Student and Intellectual Observer for July contains several 
good articles, though none of any striking originality. The 
longest is by Dr. W. B. Carpenter, on the Deep Sea, its Physi- 
cal Conditions, apparently a report of a lecture delivered during 
the winter in St. George’s Hall. Dr. Henry White’s article on 
Demonism and Convulsionism gives some interesting details of 
the epidemic which prevailed in Europe during the 17th century. 
Dr. Wickham Legg, on Zymotics, discusses the theory of the 
fungus-germ theory of diseases of this class, which he admits ex- 
plains a good many- of the facts, but demands too great a con- 
cession in the outset, in the presence in the blood of nearly twenty 
distinct and separate substances, which exist only to serve as a 
nidus for the specific ferment, and to be a source of injury to 
the individual. Mr. Llewellynn Jewitt contributes an article on 
Celts and other Implements of Bronze, profusely illustrated ; 
Mr. Barff, a third article on Poisons; and Mr. Henry J. Slack, 
two short papers on the Juniper Fungus (/odisoma), and on the 
Structure of Pinnulariez. The two publications of the quarter 
selected for separate reviews are Proctor’s ‘* Other Worlds than 
Ours” and Wallace’s ‘‘ Contributions to thejTheory of Natural 
Selection ;”? and minor papers and reports fill up the number. 
