indications of volcanic phenomena of a special kind, that we are
justified in devoting a chapter to their consideration. It is very
tantalising that our beautiful satellite only permits us to look at and
admire one half of her sphere; but it is not a very far-fetched
inference if we feel satisfied that the other half bears a general
resemblance to that which is presented to the earth. It is scarcely
necessary to inform the reader why it is that we never see but one face;
still, for the sake of those who have not thought out the subject I may
state that it is because the moon rotates on her axis exactly in the
time that she performs a revolution round the earth. If this should not
be sufficiently clear, let the reader perform a very simple experiment
for himself, which will probably bring conviction to his mind that the
explanation here given is correct. Let him place an orange in the centre
of a round table, and then let him move round the table from a
starting-point sideways, ever keeping his face directed towards the
orange; and when he has reached his starting-point, he will find that he
has rotated once round while he has performed one revolution round the
table. In this case the performer represents the moon and the orange
the earth.
Now this connection between the earth and her satellite is sufficiently
close to be used as an argument (if not as actual demonstration) that
the earth and the moon were originally portions of the same mass, and
that during some very early stage in the development of the solar system
these bodies parted company, to assume for ever after the relations of
planet and satellite. At the epoch referred to, we may also suppose that
these two masses of matter were in a highly incandescent, if not even
gaseous, state; and we conclude, therefore, that having been once
portions of the same mass, they are composed of similar materials. This
conclusion is of great importance in enabling us to reason from analogy
regarding the origin of the physical features on the moon's surface, and
for the purpose of comparison with those which we find on the surface of
our globe; because it is evident that, if the composition of the moon
were essentially different from that of our earth, we should have no
basis whatever for a comparison of their physical features.
When the moon started on her career of revolution round the earth, we
may well suppose that her orbit was much smaller than at present. She
was influenced by counteracting forces, those of gravitation drawing her
towards the centre of gravity of the earth,[1] and the centrifugal
force, which in the first instance was the stronger, so that her orbit
for a lengthened period gradually increased until the two forces, those
of attraction and repulsion, came into a condition of equilibrium, and
she now performs her revolution round the earth at a mean distance of
240,000 miles, in an orbit which is only very slightly elliptical.[2]
How the period of the moon's rotation is regulated by the earth's
attraction on her molten lava-sheets, first at the surface, and now
probably below the outer crust, has been graphically shown by Sir Robert
Ball,[3] but it cannot be doubted that once the moon was appreciably
nearer to our globe than at present. The attraction of her mass produced
tides in the ocean of correspondingly greater magnitude, and capable of
effecting results, both in eroding the surface and in transporting
masses of rock, far beyond the bounds of our every-day experience.
Of all the heavenly bodies, the sun excepted, the moon is the most
impressive and beautiful. As we catch her form, rising as a fair
crescent in the western sky after sunset, gradually increasing in size
and brilliancy night after night till from her circular disk she throws
a full flood of light on our world and then passes through her
decreasing phases, we recognise her as "the Governor of the night," or
in the words of our own poet, when in her crescent phase, "the Diadem of
night." Seen through a good binocular glass, her form gains in
rotundity; but under an ordinary telescope with a four-inch objective,
she appears like a globe of molten gold. Yet all this light is
derivative, and is only a small portion of that she receives from the
sun. That her surface is a mass of rigid matter destitute of any
inherent brilliancy, appears plain enough when we view a portion of her
disk through a very large telescope. It was the good fortune of the
author to have an opportunity for such a view through one of the largest
telescopes in the world. The 27-inch refractor manufactured by Sir
Howard Grubb of Dublin, for the Vienna observatory, a few years ago, was
turned on a portion of the moon's disk before being finally sent off to
its destination; and seen by the aid of such enormous magnifying power,
nothing could be more disappointing as regards the appearance of our
satellite. The sheen and lustre of the surface was now observed no
longer; the mountains and valleys, the circular ridges and hollows were,
indeed, wonderfully defined and magnified, but the matter of which they
seemed to be constituted resembled nothing so much as the pale plaster
of a model. One could thus fully realise the fact that the moon's light
is only derivative. Still we must recollect that the most powerful
telescope can only bring the surface of the moon to a distance from us
of about 250 miles; and it need not be said that objects seen at such a
distance on our earth present very deceptive appearances; so that we
gain little information regarding the composition of the moon's crust,
or exterior surface, simply from observation by the aid of large
telescopes.
Reasoning from analogy with our globe, we may infer that the exterior
shell of the moon consists of crystalline volcanic matter of the highly
silicated, or acid, varieties resting upon another of a denser
description, rich in iron, and resembling basalt. This hypothesis is
hazarded on the supposition that the composition of the matter of the
moon's mass resembles in the main that of our globe. During the process
of cooling from a molten condition, the heavier lavas would tend to fall
inwards, and allow the lighter to come to the surface, and form the
outer shell in both cases. Thus, the outer crust would resemble the
trachytic lavas of our globe, and their pale colour would enable the
sun's rays to be reflected to a greater extent than if the material were
of the blackness of basalt.[4] So much for the material. We have now to
consider the structure of the moon's surface, and here we find ourselves
treading on less speculative and safer ground. All astronomers since the
time of Schroter seem to be of accord in the opinion that the remarkable
features of the moon's surface are in some measure of volcanic origin,
and we shall presently proceed to consider the character of these forms
more in detail.
But first, and as leading up to the discussion of these physical
features, we must notice one essential difference between the
constitution of the moon and of the earth; namely, the absence of water
and of an atmosphere in the case of the moon. The sudden and complete
occultation of the stars when the moon's disk passes between them and
the place of the observer on the earth's surface, is sufficient evidence
of the absence of air; and, as no cloud has ever been noticed to veil
even for a moment any part of our satellite's face, we are pretty safe
in concluding that there is no water; or at least, if there be any, that
it is inappreciable in quantity.[5] Hence we infer that there is no
animal or vegetable life on the moon's surface; neither are there
oceans, lakes or rivers, snowfields or glaciers, river-valleys or
canyons, islands, stratified rocks, nor volcanoes of the kind most
prevalent on our own globe.
[Illustration: Fig. 38.--Photograph of the moon's surface (in part)
showing the illuminated "spots," and ridges, and the deep hollows. The
position of "Tycho" is shown near the upper edge, and some of the
volcanic craters are very clearly seen near the margin.]
Now on looking at a photographic picture of the moon's surface (Fig.
38), we observe that there are enormous dark spaces, irregular in
outline, but more or less approaching the circular form, surrounded by
steep and precipitous declivities, but with sides sloping outwards.
These were supposed at one time to be seas; and they retain the name,
though it is universally admitted that they contain no water. Some of
these hollows are four English miles in depth. The largest of these,
situated near the north pole of the moon, is called _Mare Imbrium_; next
to it is _Mare Serenitatis_; next, _Mare Tranquilitatis_, with several
others.[6] Mare Imbrium is of great depth, and from its floor rise
several conical mountains with circular craters, the largest of which,
_Archimedes_, is fifty miles in diameter; its vast smooth interior being
divided into seven distinct zones running east and west. There is no
central mountain or other obvious internal sign of former volcanic
activity, but its irregular wall rises into abrupt towers, and is marked
outside by decided terraces.[7]
The Mare Imbrium is bounded along the east by a range of mountains
called the _Apennines_, and towards the north by another range called
the _Alps_; while a third range, that of the _Caucasus_, strikes
northward from the junction of the two former ranges. Several circular
or oval craters are situated on, and near to, the crest of these ridges.
[Illustration: Fig. 39.--A magnified portion of the moon's surface,
showing the forms of the great craters with their outer ramparts. The
white spot with shadow is a cone rising from the centre of one of the
larger craters to a great height and thus becoming illuminated by the
sun's light.]
But the greater part of the moon's hemisphere is dotted over by almost
innumerable circular crater-like hollows; sometimes conspicuously
surmounting lofty conical mountains, at other times only sinking below
the general outer surface of the lunar sphere. On approaching the
margin, these circular hollows appear oval in shape owing to their
position on the sphere; and the general aspect of those that are visible
leads to the conclusion that there are large numbers of smaller craters
too small to be seen by the most powerful telescopes. These cones and
craters are the most characteristic objects on the whole of the visible
surface, and when highly magnified present very rugged outlines,
suggestive of slag, or lava, which has consolidated on cooling, as in
the case of most solidified lava-streams on our earth.[8] One of the
most remarkable of these crateriform mountains is that named
_Copernicus_, situated in a line with the southern prolongation of the
Apennines. Of this mountain Sir R. Ball says: "It is particularly well
known through Sir John Herschel's drawing, so beautifully reproduced in
the many editions of the _Outlines of Astronomy_. The region to the west
is dotted over with innumerable minute craterlets. It has a central,
many-peaked mountain about 2,400 feet in height. There is good reason to
believe that the terracing shown in its interior is mainly due to the
repeated alternate rise, partial congealation and retreat of a vast sea
of lava. At full moon it is surrounded by radiating streaks."[9] The
view regarding the structure of Copernicus here expressed is of
importance, as it is probably applicable to all the craters of our
satellite.
"When the moon is five or six days old," says Sir Robert Ball, "a
beautiful group of three craters will be readily found on the boundary
line between night and day. These are _Catharina_, _Cyrillus_, and
_Theophilus_. Catharina is the most southerly of the group, and is more
than 16,000 feet deep and connected to Cyrillus by a wide valley; but
between Cyrillus and Theophilus there is no such connection. Indeed
Cyrillus looks as if its huge surrounding ramparts, as high as Mont
Blanc, had been completely finished when the volcanic forces commenced
the formation of Theophilus, the rampart of which encroaches
considerably on its older neighbour. Theophilus stands as a well-defined
round crater, about 64 miles in diameter, with an internal depth of
14,000 to 18,000 feet, and a beautiful central group of mountains,
one-third of that height, on its floor. This proves that the last
eruptive efforts in this part of the moon fully equalled in intensity
those that had preceded them. Although Theophilus is on the whole the
deepest crater we can see in the moon, it has received little or no
deformation by secondary eruptions."
But perhaps the most remarkable object on the whole hemisphere of the
moon is "the majestic Tycho," which rises from the surface near the
south pole, and at a distance of about 1/6th of the diameter of the
sphere from its margin. Its depth is stated by Ball to be 17,000 feet,
and its diameter 50 miles. But its special distinction amongst the other
volcanic craters lies in the streaks of light which radiate from it in
all directions for hundreds and even thousands of miles, stretching with
superb indifference across vast plains, into the deepest craters, and
over the highest opposing ridges. When the sun rises on Tycho these
streaks are invisible, but as soon as it has reached a height of 25 deg. to
30 deg. above the horizon, the rays emerge from their obscurity, and
gradually increase in brightness until full moon, when they become the
most conspicuous objects on her surface. As yet no satisfactory
explanation has been given of the origin of these illuminated rays,[10]
but I may be permitted to add that their form and mode of occurrence are
eminently suggestive of gaseous exhalations from the volcano illumined
by the sun's rays; and owing to the absence of an atmosphere, spreading
themselves out in all directions and becoming more and more attenuated
until they cease to be visible.
The above account will probably suffice to give the reader a general
idea of the features and inferential structure of the moon's surface.
That she was once a molten mass is inferred from her globular form; but,
according to G. F. Chambers, the most delicate measurements indicate no
compression at the poles.[11] That her surface has cooled and become
rigid is also a necessary inference; though Sir J. Herschel considered
that the surface still retains a temperature _possibly_ exceeding that
of boiling water.[12] However this may be, it is pretty certain that
whatever changes may occur upon her surface are not due to present
volcanic action, all evidence of such action being admittedly absent.
If, when the earth and moon parted company, their respective
temperatures were equal, the moon being so much the smaller of the two
would have cooled more rapidly, and the surface may have been covered by
a rigid crust when as yet that of the earth may have been molten from
heat. Hence the rigidity of the moon's surface may date back to an
immensely distant period, but she may still retain a high temperature
within this crust. Having arrived at this stage of our narrative, we are
in a position to consider by what means, and under what conditions, the
cones and craters which diversify the lunar surface have been developed.
In doing so it may be desirable, in the first place, to determine what
form of crater on our earth's surface those of the moon do not
represent; and we are guided in our inquiry by the consideration of the
absence of water on the lunar surface. Now there are large numbers of
crateriform mountains on our globe in the formation of which water has
played an important, indeed essential, part. As we have already seen,
water, though not the ultimate cause of volcanic eruptions, has been the
chief agent, when in the form of steam at high pressure, in producing
the explosions which accompany these eruptions, and in tearing up and
hurling into the air the masses of rock, scoriae, and ashes, which are
piled around the vents of eruption in the form of craters during periods
of activity. To this class of craters those of Etna, Vesuvius, and
Auvergne belong. These mountains and conical hills (the domes excepted)
are all built up of accumulations of fragmental material, with
occasional sheets and dykes of lava intervening; and where eruptions
have taken place in recent times, observation has shown that they are
accompanied by outbursts of vast quantities of aqueous vapour, which has
been the chief agent (along with various gases) in piling up the
circular walls of the crater.
It has also been shown that in many instances these crater-walls have
been breached on one side, and that streams of molten lava which once
occupied the cup to a greater or less height, have poured down the
mountain side. Hence the form or outline of many of these fragmental
craters is crescent-shaped. Such breached craters are to be found in all
parts of the world, and are not confined to any one district, or even
continent, so that they may be considered as characteristic of the class
of volcanic crater-cones to which I am now referring. In the case of the
moon, however, we fail to observe any decided instances of breached
craters, with lava-streams, such as those I have described.[13] In
nearly all cases the ramparts appear to extend continuously round the
enclosed depression, solid and unbroken; or at least with no large gap
occupying a very considerable section of the circumference. (See Fig.
38.) Hence we are led to suspect that there is some essential
distinction between the craters on the surface of the moon and the
greater number of those on the surface of our earth.
It is scarcely necessary to add that the volcanic mountains of the moon
offer no resemblance whatever to the dome-shaped volcanic mountains of
our globe. If it were otherwise, the lunar mountains would appear as
simple luminous points rising from a dark floor, over which they would
cast a conical shadow. But the form of the lunar volcanic mountains is
essentially different; as already observed, they consist in general of a
circular rampart enclosing a depressed floor, sometimes terraced as in
the case of Copernicus, from which rise one or more conical mountains,
which are in effect the later vents of eruption.
In our search, therefore, for analogous forms on our own earth, we must
leave out the craters and domes of the type furnished by the European
volcanoes and their representatives abroad, and have recourse to others
of a different type. Is there then, we may ask, any type of volcanic
mountain on our globe comparable with those on the moon? In all
probability there is.
If the reader will turn to the description of the volcanoes of the
Hawaiian group in the Pacific, especially that of Mauna Loa, as given by
Professor Dana and others, and compare it with that of Copernicus, he
will find that in both cases we have a circular rampart of solid lava
enclosing a vast plain of the same material from which rise one or more
lava-cones. The interiors in both cases are terraced. So that, allowing
for differences in magnitude, it would seem that there is no essential
distinction between lunar craters and terrestrial craters of the type of
Mauna Loa. Dana calls these Hawaiian volcanoes "basaltic," basalt being
the prevalent material of which they are formed. Those of the moon may
be composed of similar material, or otherwise; but in either case we may
suppose they are built up of lava, erupted from vents connected with the
molten reservoirs of the interior. Thus we conclude that they belong to
an entirely different type, and have been built up in a different
manner, from those represented by Etna, Vesuvius, and most of the
extinct volcanoes of Auvergne, the Eifel, and of other districts
considered in these pages.
Let us now endeavour to picture to ourselves the stages through which
the moon may be supposed to have passed from the time her surface began
to consolidate owing to the radiation of her heat into space; for there
is every probability that some of the craters now visible on her disk
were formed at a very early period of her physical history.
When the surface began to consolidate, it must also have contracted; and
the interior molten matter, pressed out by the contracting crust, must
have been over and over again extruded through fissures produced over
the solidified surface, until the solid crust extended over the whole
lunar surface, and became of considerable thickness.
It is from this epoch that, in all probability, we should date the
commencement of what may be termed "the volcanic history" of the moon.
We must bear in mind that although the moon's surface had become solid,
its temperature may have remained high for a very long period. But the
continuous radiation of the surface-heat into space would produce
continuous contraction, while the convection of the interior heat would
tend to increase the thickness of the outer solid shell; and this, ever
pressing with increasing force on the interior molten mass, would result
in frequent ruptures of the shell, and the extrusion of molten lava
rising from below. Hence we may suppose the fissure-eruptions of lava
were of frequent occurrence for a lengthened period during the early
stage of consolidation of the lunar crust; but afterwards these may be
supposed to have given place to eruptions through pipes or vents,
resulting in the formation of the circular craters which form such
striking and characteristic objects in the physical aspect of our
satellite.[14]
It is not to be supposed that the various physical features on the lunar
surface have all originated in the same way. The great ranges of
mountains previously described may have originated by a process of
piling up of immense masses of molten lava extruded from the interior
through vents or fissures; while the great hollows (or "seas") are
probably due to the falling inwards of large spaces owing to the escape
of the interior lava.
But it is with the circular craters that we are most concerned. Judging
from analogy with the lava-craters present on our globe, we must suppose
them to be due to the extrusion, and piling up, of lava through central
pipes, followed in some cases by the subsidence of the floor of the
crater. It seems not improbable that it was in this way the greater
number of the circular craters lying around Tycho, and dotting so large
a space round the margin of the moon, were constructed. (See Fig. 38.)
In general they appear to consist of an elevated rim, enclosing a
depressed plain, out of which a central cone arises. The rim may be
supposed to have been piled up by successive discharges of lava from a
central orifice; and after the subsidence of the paroxysm the lava still
in a molten condition may have sunk down, forming a seething lake within
the vast circular rampart, as in the case of the Hawaiian volcanoes. The
terraces observable within the craters in some instances have probably
been left by subsequent eruptions which have not attained to the level
of preceding ones; and where a central crater-cone is seen to rise
within the caldron, we may suppose this to have been built up by a later
series of eruptions of lava through the original pipe after the
consolidation of the interior sea of lava. The mamelons of the Isle of
Bourbon,[15] and some of the lava-cones of Hawaii, appear to offer
examples on our earth's surface of these peculiar forms.
Such are the views of the origin of the physical features of our
satellite which their form and inferred constitution appear to suggest.
They are not offered with any intention of dogmatising on a subject
which is admittedly obscure, and regarding which we have by no means all
the necessary data for coming to a clear conclusion. All that can be
affirmed is, that there is a great deal to be said in support of them,
and that they are to some extent in harmony with phenomena within range
of observation on the surface of our earth.
The far greater effects of lunar vulcanicity, as compared with those of
our globe, may be accounted for to some extent by the consideration that
the force of gravity on the surface of the moon is only one-sixth of
that on the surface of the earth. Hence the eruptive forces of the
interior of our satellite have had less resistance to overcome than in
the case of our planet; and the erupted materials have been shot forth
to greater distances, and piled up in greater magnitude, than with us.
We have also to recollect that the abrading action of water has been
absent from the moon; so that, while accumulations of matter had been
proceeding throughout a prolonged period over its surface, there was no
counteracting agency of denudation at work to modify or lessen the
effects of the ruptive forces.
[1] Correctly speaking, each attracts the other towards its centre of
gravity with a force proportionate to its mass, and inversely as the
square of the distance; but the earth being by much the larger body, its
attraction is far greater than that of the moon.
[2] The variation in the distance is only under rare circumstances
40,000 miles, but ordinarily about 13,000 miles.
[3] _Story of the Heavens_, 2nd edition, p. 525, _et seq._
[4] A series of researches made by Zoellner, of Leipzig, led him to
assign to the light-reflecting capacity of the full-moon a result
intermediate between that obtained by Bouguer, which gave a brightness
equal to 1/300000 part of that of the sun, and of Wollaston, which gave
1/801070 part. We may accept 1/618000 of Zoellner as sufficiently close;
so that it would require 600,000 full moons to give the same amount of
light as that of the sun.
[5] Schroter, however, came to the conclusion that the moon has an
atmosphere.
[6] A chart of the moon's surface, with the names of the principal
physical features, will be found in Ball's _Story of the Heavens_, 2nd
edit., p. 60. It must be remembered that the moon as seen through a
telescope appears in reversed position.
[7] _Ibid._, p. 66.
[8] As represented by Nasmyth's models in plaster.
[9] Ball, _loc. cit._, p. 67.
[10] Ball, _loc. cit._, p. 69.
[11] _Astronomy_, p. 78.
[12] _Outlines of Astronomy_, p. 285.
[13] At rare intervals a few crescent-shaped ridges are discernible on
the lunar sphere, but it is very doubtful if they are to be regarded as
breached craters.
[14] The number of "spots" on the moon was considered to be 244 until
Schroter increased it to 6,000, and accurately described many of them.
Schroter seems to have been the earliest observer who identified the
circular hollows on the moon's surface as volcanic craters.
[15] Drawings of these very curious forms are given by Judd,
_Volcanoes_, p. 127.
CHAPTER III.
ARE WE LIVING IN AN EPOCH OF SPECIAL VOLCANIC ACTIVITY?
The question which we are about to discuss in the concluding chapter of
this volume is one to which we ought to be able to offer a definite
answer. This can only be arrived at by a comparison of the violence and
extent of volcanic and seismic phenomena within the period of history
with those of pre-historic periods.
At first sight we might be disposed to give to the question an
affirmative reply when we remember the eruptions of the last few years,
and add to these the volcanic outbursts and earthquake shocks which
history records. The cases of the earthquake and eruption in Japan of
November, 1891, where in one province alone two thousand people lost
their lives and many thousand houses were levelled[1]; that of Krakatoa,
in 1883; of Vesuvius, in 1872; and many others of recent date which
might be named, added to those which history records;--the recollection
of such cases might lead us to conclude that our epoch is one in which
the subterranean volcanic forces had broken out with extraordinary
energy over the earth's surface. Still, when we come to examine into
the cases of recorded eruptions--especially those of great violence--we
find that they are limited to very special districts; and even if we
extend our retrospect into the later centuries of our era, we shall find
that the exceptionally great eruptions have been confined to certain
permanently volcanic regions, such as the chain of the Andes, that of
the Aleutian, Kurile, Japanese, and Philippine and Sunda Islands, lying
for the most part along the remarkable volcanic girdle of the world to
which I have referred in a previous page. Add to these the cases of
Iceland and the volcanic islands of the Pacific, and we have almost the
whole of the very active volcanoes of the world.
Then for the purposes of our inquiry we have to ascertain how these
active vents of eruption compare, as regards the magnitude of their
operations, with those of the pre-historic and later Tertiary times. But
before entering into this question it maybe observed, in the first
place, that a large number of the vents of eruption, even along the
chain of the earth's volcanic girdle, are dormant or extinct. This
observation applies to many of the great cones and domes of the Andes,
including Chimborazo and other colossal mountains in Ecuador, Columbia,
Chili, Peru, and Mexico. The region between the eastern Rocky Mountains
and the western coast of North America was, as we have seen, one over
which volcanic eruptions took place on a vast scale in later Tertiary
times; but one in which only the after-effects of volcanic action are at
present in operation. We have also seen that the chain of volcanoes of
Japan and of the Kurile Islands are only active to a slight extent as
compared with former times, and the same observation applies to those
of New Zealand. Out of 130 volcanoes in the Japanese islands, only 48
are now believed to be active.
Again, if we turn to other districts we have been considering, we find
that in the Indian Peninsula, in Arabia, in Syria and the Holy Land, in
Persia, in Abyssinia and Asia Minor--regions where volcanic operations
were exhibited on a grand scale throughout the Tertiary period, and in
some cases almost down into recent times--we are met by similar
evidences either of decaying volcanic energy, or of an energy which, as
far as surface phenomena are concerned, is a thing of the past. Lastly,
turning our attention to the European area, notwithstanding the still
active condition of Etna, Vesuvius, and a few adjoining islands, we see
in all directions throughout Southern Italy evidences of volcanic
operations of a past time,--such as extinct crater-cones, lakes
occupying the craters of former volcanoes, and extensive deposits of
tuff or streams of lava--all concurring in giving evidence of a period
now past, when vulcanicity was widespread over regions where its
presence is now never felt except when some earthquake shock, like that
of the Riviera, brings home to our minds the fact that the motive force
is still beneath our feet, though under restrained conditions as
compared with a former period.
Similar conclusions are applicable with even greater force to other
parts of the European area. The region of the Lower Rhine and Moselle,
of Hungary and the Carpathians, of Central France, of the North of
Ireland and the Inner Hebrides, all afford evidence of volcanic
operations at a former period on an extensive scale; and the contrast
between the present physically silent and peaceful condition of these
regions, as regards any outward manifestations of sub-terrestrial
forces, compared with those which were formerly prevalent, cannot fail
to impress our minds irresistibly with the idea that volcanic energy has
well-nigh exhausted itself over these tracts of the earth's surface.
From this general survey of the present condition of the earth's
surface, as regards the volcanic operations going on over it, and a
comparison with those of a preceding period, we are driven to the
conclusion that, however violent and often disastrous are the volcanic
and seismic phenomena of the present day, they are restricted to
comparatively narrow limits; and that even within these limits the
volcanic forces are less powerful than they were in pre-historic times.
The middle part of the Tertiary period appears, in fact, to have been
one of extraordinary volcanic activity, whether we regard the wide area
over which this activity manifested itself, or the results as shown by
the great amount of the erupted materials. Many of the still active
volcanic chains, or groups, probably had their first beginnings at the
period referred to; but in the majority of cases the eruptive forces
have become dormant or extinct. With the exception of the lavas of the
Indian-Peninsular area, which appear, at least partially, to belong to
the close of the Cretaceous epoch, the specially volcanic period may be
considered to extend from the beginning of the Miocene down to the close
of the Pliocene stage. During the Eocene stage, volcanic energy appears
to have been to a great degree dormant; but plutonic energy was
gathering strength for the great effort of the Miocene epoch, when the
volcanic forces broke out with extraordinary violence over Europe, the
British Isles, and other regions, and continued to develop throughout
the succeeding Pliocene epoch, until the whole globe was surrounded by a
girdle of fire.
* * * * *
The reply, therefore, to the question with which we set out is very
plain; and is to the effect that the present epoch is one of
comparatively low volcanic activity. The further question suggests
itself, whether the volcanic phenomena of the middle Tertiary period
bear any comparison with those of past geological times. This, though a
question of great interest, is one which is far too large to be
discussed here; and it is doubtful if we have materials available upon
which to base a conclusion. But it may be stated with some confidence,
in general terms, that the history of the earth appears to show that,
throughout all geological time, our world has been the theatre of
intermittent geological activity, periods of rest succeeding those of
action; and if we are to draw a conclusion regarding the present and
future, it would be that, owing to the lower rate of secular cooling of
the crust, volcanic action ought to become less powerful as the world
grows older.
[1] Admirably illustrated in Prof. J. Milne's recently published work,
_The Great Earthquake of Japan, 1891_.
APPENDIX.
A BRIEF ACCOUNT OF THE PRINCIPAL VARIETIES OF VOLCANIC ROCKS.
The text-books on this subject are so numerous and accessible, that a
very brief account of the volcanic rocks is all that need be given here
for the purposes of reference by readers not familiar with petrological
details.
Let it be observed, in the first place, that there is no hard and fast
line between the varieties of igneous and volcanic rocks. In this as in
other parts of creation--_natura nil facit per saltum_; there are
gradations from one variety to the other. At the same time a systematic
arrangement is not only desirable, but necessary; and the most important
basis of arrangement is that founded on the proportion of _silica_ (or
quartz) in the various rocks, as first demonstrated by Durocher and
Bunsen, who showed that silica plays the same part in the inorganic
kingdom that carbon does in the organic. Upon this hypothesis, which is
a very useful one to work with, these authors separated all igneous and
volcanic rocks into two classes, viz., the Basic and the Acid; the
former containing from 45-58 per cent., the latter 62-78 per cent. of
that mineral. But there are a few intermediate varieties which serve to
bridge over the space between the Basic and Acid Groups. The following
is a generalised arrangement of the most important rocks under the above
heads:--
_Tabular View of Chief Igneous and Volcanic Rocks._
BASIC GROUP.
1. Basalt and Dolerite.
2. Gabbro.
3. Diorite.
4. Diabase and Melaphyre.
5. Porphyrite.
INTERMEDIATE GROUP.
6. Syenite.
7. Mica-trap, or Lampophyre.
8. Andesite.
ACID GROUP.
9. Trachyte, Domite, and Phonolite.
10. Rhyolite and Obsidian.
11. Granophyre.
12. Granite.
In the above grouping, and in the following definitions, I have not been
able to follow any special authority. But the most serviceable
text-books are those of Mr. Frank Rutley, _Study of Rocks_, and Dr.
Hatch, _Petrology_; also H. Rosenbusch, _Mikroskopische Physiographie
der Mineralien_, and F. Zirkel's _Untersuchungen ueber mikroskopische
Structur der Basaltgesteine_. We shall consider these in the order above
indicated:--
1. BASALT.--The most extensively distributed of all volcanic rocks. It
is a dense, dark rock of high specific gravity (2.4-2.8), consisting of
plagioclase felspar (Labradorite or anorthite), augite, and
titano-ferrite (titaniferous magnetite). Olivine is often present; and
when abundant the rock is called "olivine-basalt." In the older rocks,
basalt has often undergone decomposition into melaphyre; and amongst the
metamorphic rocks it has been changed into diorite or hornblende rock;
the augite having been converted into hornblende.
When leucite or nepheline replaces plagioclase, the rock becomes a
leucite-basalt,[1] or nepheline-basalt. Some basalts have a glass paste,
or "ground-mass," in which the minerals are enclosed.
The lava of Vesuvius may be regarded as a variety of basalt in which
leucite replaces plagioclase, although this latter mineral is also
present. Zirkel calls it "Sanidin-leucitgestein," as both the
macroscopic and microscopic structure reveal the presence of leucite,
sanidine, plagioclase, nephiline, augite, mica, olivine, apatite, and
magnetite.[2]
_Dolerite_ does not differ essentially from basalt in composition or
structure, but is a largely crystalline-granular variety, occurring more
abundantly than basalt amongst the more ancient rocks, and the different
minerals are distinctly visible to the naked eye.
A remarkable variety of this rock occurs at Slieve Gullion in Ireland,
in which mica is so abundant as to constitute the rock a "micaceous
dolerite."
2. GABBRO.--A rather wide group of volcanic rocks with variable
composition. Essentially it is a crystalline-granular compound of
plagioclase, generally Labradorite and diallage. Sometimes the pyroxenic
mineral becomes hypersthene, giving rise to _hypersthene-gabbro_; or
when hornblende is present, to _hornblende-gabbro_; when olivine, to
_olivine-gabbro_. Magnetite is always present.
These rocks occur in the Carlingford district in Ireland, in the Lizard
district of Cornwall, the Inner Hebrides (Mull, Skye, etc.) of Scotland,
and in Saxony.
3. DIORITE.--A crystalline-granular compound of plagioclase and
hornblende with magnetite. When quartz is present it becomes (according
to the usual British acceptation) a _syenite_; but this view is
gradually giving place to the German definition of syenite, which is a
compound of orthoclase and hornblende; and it may be better to
denominate the variety as _quartz-diorite_. The diorites are abundant as
sheets and dykes amongst the older palaeozoic and metamorphic rocks, and
are sometimes exceedingly rich in magnetite. Mica, epidote, and chlorite
are also present as accessories.
The rock occurs in North Wales, Charnwood Forest, Wicklow, Galway, and
Donegal, and the Highlands of Scotland. There can be little doubt that
amongst the metamorphic rocks of Galway, Mayo, and Donegal the great
beds of (often columnar) diorite were originally augitic lavas, which
have since undergone transformation.
4. DIABASE.--It is very doubtful if "Diabase" ought to be regarded as a
distinct species of igneous rock, as it seems to be simply an altered
variety of basalt or dolerite, in which chlorite, a secondary
alteration-product, has been developed by the decomposition of the
pyroxene or olivine of the original rock. It is a convenient name for
use in the field when doubt occurs as to the real nature of an igneous
rock. Melaphyre is a name given to the very dark varieties of altered
augitic lavas, rich in magnetite and chlorite.
5. PORPHYRITE (or quartzless porphyry).--A basic variety of
felstone-porphyry, consisting of a felspathic base with distinct
crystals of felspar, with which there may be others of hornblende, mica,
or augite. The colour is generally red or purple, and it weathers into
red clay, in contrast to the highly acid or silicated felsites which
weather into whitish sand.
6. SYENITE.--As stated above, this name has been variously applied. Its
derivation is from Syene (Assouan) in Egypt, and the granitic rocks of
that district were called "syenites," under the supposition (now known
to be erroneous) that they differ from ordinary granites in that they
were supposed to be composed of quartz, felspar, and hornblende, instead
of quartz, felspar, and mica. From this it arose that syenite was
regarded as a variety of granite in which the mica is replaced by
hornblende, and this has generally been the British view of the
question. But the German definition is applied to an entirely different
rock, belonging to the felstone family; and according to this
classification syenite consists of a crystalline-granular compound of
orthoclase and hornblende, in which quartz may or may not be present.
From this it will be seen that, according to Zirkel, syenite is
essentially distinct from diorite in the species of its felspar.[3] It
seems desirable to adopt the German view; and as regards diorites
containing quartz as an accessory, to apply to them the name of
_quartz-diorite_, as stated above, the name syenite as used by British
geologists having arisen from a misconception.
7. MICA-TRAP (LAMPOPHYRE).--A rock, allied to the felstone family, in
which mica is an abundant and essential constituent, thus consisting of
plagioclase and mica, with a little magnetite. Quartz may be an
accessory. This rock occurs amongst the Lower Silurian strata of
Ireland, Cumberland, and the South of Scotland; it is not volcanic in
the ordinary acceptation of that term. The term _lampophyre_ was
introduced by Guembel in describing the mica-traps of Fichtelgebirge.
8. ANDESITE.--This is a dark-coloured, compact or vesicular,
semi-vitreous group of volcanic rocks, composed essentially of a glassy
plagioclase felspar, and a ferro-magnesian constituent enclosed in a
glassy base. According to the nature of the ferro-magnesian constituent,
the group may be divided into _hornblende-andesite_, _biotite-andesite_,
and _augite-andesite_. Quartz is sometimes present, and when this
mineral becomes an essential it gives rise to a variety called
_quartz-andesite_ or _dacite_.
These rocks are the principal constituents of the lavas of the Andes,
and the name was first applied to them by Leopold von Buch; but their
representatives also occur in the British Isles, Germany, and elsewhere.
Dacite is the lava of Krakatoa and some of the volcanoes of Japan.
9, 10. TRACHYTE and DOMITE, etc.--These names include very numerous
varieties of highly silicated volcanic rock, and in their general form
consist of a white felsitic paste with distinct crystals of sanidine,
together with plagioclase, augite, biotite, hornblende, and accessories.
When crystalline grains or blebs of quartz occur, we have a
quartz-trachyte; when tridymite is abundant, as in the trachyte of Co.
Antrim, we have "tridymite-trachyte."
The trachytes occupy a position between the pitchstone lavas on the one
hand, and the andesites and granophyres on the other.
(_b._) _Domite_ is the name applied to the trachytic rocks of the
Auvergne district and the Puy de Dome particularly. They do not contain
free quartz, though they are highly acid rocks, containing sometimes as
much as 68 per cent. of silica.
(_c._) _Phonolite (Clinkstone)_ is a trachytic rock, composed
essentially of sanidine, nepheline, and augite or hornblende. It is
usually of a greenish colour, hard and compact, so as to ring under the
hammer; hence the name. The Wolf Rock is composed of phonolite, and it
occurs largely in Auvergne.
(_d._) _Rhyolites_ are closely connected with the _quartz-trachytes_,
but present a marked fluidal, spherulitic, or perlitic structure. They
consist of a trachytic ground-mass in which grains or crystals of
quartz and sanidine, with other accessory minerals, are imbedded. They
occur amongst the volcanic rocks of the British Isles, Hungary, and the
Lipari Islands, from which the name _Liparite_ has been derived.
(_e._) _Obsidian (Pitchstone)._--This is a vitreous, highly acid rock,
which has become a volcanic glass in consequence of rapid cooling,
distinct minerals not having had time to form. It has a conchoidal
fracture, various shades of colour from grey to black; and under the
microscope is seen to contain crystallites or microliths, often
beautifully arranged in stellate or feathery groups. Spherulitic
structure is not infrequent; and occasionally a few crystals of
sanidine, augite, or hornblende are to be seen imbedded in the glassy
ground-mass. The rock occurs in dykes and veins in the Western Isles of
Scotland, in Antrim, and on the borders of the Mourne Mountains, near
Newry, in Ireland.
11. GRANOPHYRE.--This term, according to Geikie, embraces the greater
portion of the acid volcanic rocks of the Inner Hebrides. They are
closely allied to the quartz-porphyries, and vary in texture from a fine
felsitic or crystalline-granular quartz-porphyry, in the ground-mass of
which porphyritic turbid felspar and quartz may generally be detected,
to a granitoid rock of medium grain, in which the component dull felspar
and clear quartz can be readily distinguished by the naked eye.
Throughout all the varieties of texture there is a strong tendency to
the development of minute irregularly-shaped cavities, inside of which
quartz or felspar has crystallised out--a feature characteristic of the
granites of Arran and of the Mourne Mountains.
12. GRANITE.--A true granite consists of a crystalline-granular rock
consisting of quartz, felspar (orthoclase), and mica; the quartz is the
paste or ground-mass in which the felspar and mica crystals are
enclosed. This is the essential distinction between a granite and a
quartz-porphyry or a granophyre. Owing to the presence of highly-heated
steam under pressure in the body of the mass when in a molten condition,
the quartz has been the last of the minerals to crystallise out, and
hence does not itself occur with the crystalline form.
True granite is not a volcanic rock, and its representatives amongst
volcanic ejecta are to be found in the granophyres, quartz-porphyries,
felsites, trachytes, and rhyolites so abundant in most volcanic
countries, and to one or other of these the so-called granites of the
Mourne Mountains, of Arran Island, and of Skye are to be referred.
Granite is a rock which has been intruded in a molten condition
amongst the deep-seated parts of the crust, and has consolidated
under great pressure in presence of aqueous vapour and with extreme
slowness, resulting in the formation of a rock which is largely
crystalline-granular. Its presence at the surface is due to denudation
of the masses by which it was originally overspread.
[Illustration: Plate I.]
EXPLANATION OF PLATE I.
MAGNIFIED SECTIONS OF VESUVIAN MINERALS.
Fig. 1. Section of leucite crystal from the lava of 1868, with
fluid cavities. Mag., 350 diams.
" 2, 3, 4, and 5. Sections of nepheline crystals from the lava of
1767, 1834, and 1854.
" 6. Section of sodalite crystal from the lava of 1794, with
belonites and crystals of magnetite enclosed.
" 7, 8, 9. Crystals of leucite with microliths and cavities
darkened by magnetite dust; also, containing crystals of
magnetite.
" 10. Group of leucite crystals of irregular form from the lava of
1855, congregated around a nucleus of crystals of plagioclase
and magnetite.
[Illustration: Plate II.]
EXPLANATION OF PLATE II.
MAGNIFIED SECTIONS OF VESUVIAN MINERALS.
Fig. 1. Section of augite crystal from the lava of 1794, with
numerous gas cells and delicately banded walls. The interior
contains two long prisms, probably of apatite.
" 2. Crystal of augite with banded walls, and indented by leucite
crystals, from the lava of 1794. Mag., 40 diams.
" 3, 4, 5. Sections of augite crystals from the lavas of 1794 and
1820.
" 6. Group of augite crystals from the lava of 1835.
" 7. Ditto from the lava of 1822, with encluded mica-flake (_a_)
and portion of the glass paste, or ground-mass, of the rock
(_b_), containing microliths and grains of magnetite.
Fig. 8. Two crystals of olivine from the lava of 1855; they are
intersected on one side by the plane of the thin section, and
are remarkable for showing lines of gas cells, and bands of
growth sometimes cellular. Mag., 40 diams.
" 9. Section of rock-crystal (quartz), with double terminal
pyramids, from the lava of 1850.
" 10. Twin crystal of sanidine from the lava of 1858. Mag., 40
diams.
" 11, 12, 13. Sections of plagioclase crystals (probably
labradorite) from the lava of 1855. Mag., 100 diams.
" 14. Section of olivine crystal from the lava of 1631--imperfectly
formed. Mag., 30 diams.
" 15. Section of mica-flake from the lava of 1822. Mag., 30 diams.
[Illustration: Plate III.]
EXPLANATION OF PLATE III.
MAGNIFIED SECTIONS OF VOLCANIC ROCKS.
1. Diorite dyke, traversing Assynt limestone, North Highlands.
2. Basalt from upper beds, near Giant's Causeway, County Antrim.
3. Hornblende-hypersthene-augite Andesite, from Pichupichu, Andes.
4. Augite-Andesite from Pichupichu, Andes.
5. Olivine dolerite, with hornblende and biotite, Madagascar.
6. Leucite basalt, with mellilite, Capo di Bove, Italy.
[Illustration: Plate IV.]
EXPLANATION OF PLATE IV.
MAGNIFIED SECTIONS OF VOLCANIC ROCKS.
1. Vesuvian lava, glass paste with numerous crystals of leucite;
others of augite and nepheline porphyritically developed; also
small grains of magnetite.
2. Vesuvian lava, glass paste with numerous crystals of leucite;
others of olivine, hornblende, and sanidine, porphyritically
developed; small grains of magnetite.
3. Trachyte from Hungary; felsitic paste with crystals of
hornblende and sanidine, and a little magnetite.
4. Gabbro, from Carlingford Hill, Ireland, consisting of anorthite,
augite, a little olivine, and magnetite.
5. Dolerite, from old volcanic neck, Scalot Hill, near Lame,
consisting of labradorite, augite, olivine, and magnetite.
6. Dolerite, Ballintoy, County Antrim, showing ophetic structure,
consisting of augite, labradorite, and magnetite.
[1] Mr. S. Allport has discovered this in the rock called the "Wolf
Rock" off the coast of Cornwall. The most important work on basalt is
that by F. Zirkel, _Unters. ueber mikros. Zusammensetzung und Structur
der Basaltgesteine_. Bonn (1870).
[2] Zirkel, _Die mikroskopische Beschaffenheit der Mineralien und
Gesteine_, p. 153. Leipsig (1873).
[3] Zirkel, _Petrog._, i. 578; B. von Cotta, p. 178 (Eng. Trans.).
INDEX.
INDEX.
Abyssinian table-lands, 190 _et seq._
Albano, Lake, 89
America, volcanic regions of North, 136 _et seq._;
of Western, 144
Andes, 18, 27, 227, 254
Andesite, 263
Antrim, 154 _et seq._
Arabia, dormant volcanoes of, 126-135
Arabian desert, 134
Archibald, C. D., 213
Arizona, volcanoes of, 137
Argyll, Duke of, 173
Ascension, 36
Ashangi, volcanic series of, 192
Atmospheric effects of Krakatoa eruption, 213-214
Auckland district, volcanoes of, 147
Auvergne, volcanic regions of, 14, 16, 92 _et seq._
Azores, 32
Ball, Sir R. S., 242, 244
Basalt, 260
Blanford, W. T., 188, 189
Bonneville, Lake, 141-142
British Isles,
Tertiary volcanic districts of, 154 _et seq._, 227;
pre-Tertiary volcanic districts of, 196 _et seq._
Buch, L. von, 6, 11, 24
California, volcanoes of, 140
Callirrhoe, springs of, 133
Canyon, the Grand, 138
Cantal, volcanoes of the, 99-101
Cape Colony, Basalts of, 194
Charleston earthquake, 218, 222, 224
Chambers, G. F., 246
Charnwood Forest, 198
Chimborazo, 18
Clermont, vale of, 96-97
Clinkstone, 263
Cordilleras of Quito, 25
Cotopaxi, 16-18, 24, 26
Crater-cones, Lava, 19
Crateriform cones, 13
Craterless domes, 15
Dana, Prof. J. D., 19, 39, 249
Darwin, 28, 30
Darwin, Prof. G. H., 9, 231
Daubeny, 7, 61, 69
Davison, C., 9, 231
Davy, Sir H., 11
Deccan trap-series, 187 _et seq._
Demavend, Mount, 24
Diabase, 262
Diorite, 261
Dolerite, 261
Domite, 263
Dore, volcanoes of Mont, 100-101
Doughty, C. M., 127
Durocher, 232
Dutton, Capt. C. E., 9, 220, 222
Dykes in Ireland, 169-170
Earthquakes, 217 _et seq._
Errigal, 10
Etna, 14, 61 _et seq._, 229
Fingal's Cave, 185
Forbes, D., 27
France, extinct volcanoes of, 92 _et seq._
Gabbro, 261
Gardner, J. S., 156
Geikie, Sir A., 8, 29, 143, 156, 160, 169, 172, 176, 177, 196
Giant's Causeway, 165-166
Granite, 264
Granophyre, 264; of Mull, 174
Green, Prof. A. H., 194
Hatch, Dr., 260
Haughton, Prof., 68
Hauran, volcanoes of the, 22, 129
Haute Loire, volcanic districts of, 101-105
Hawaii, volcanoes of, 39, 249, 251
Hecla, 32
Herschel, Sir J., 244
Hibbert, Dr. S., 6, 114, 124
Hochstetter, F. von, 147
Hopkins, 171, 217
Hull, Dr. E. G., 110
Humboldt, A. von, 20, 25
Hutton, James, 5
Iceland, volcanoes of, 30-32
Ireland, volcanic Tertiary rocks of, 154 _et seq._
Jaulan, 129
Johnston-Lavis, 52
Jordan valley, 126 _et seq._, 226
Jorullo, 24
Judd, Prof., 8, 68, 69, 71, 172, 178, 208
Krakatoa, eruption of, 206 _et seq._
Kurile Islands, volcanoes of, 28
Laacher See, 121-123
Lampophyre, 262
Lancerote, 34
Lasaulx, Prof. von, 68
Lavas, relative density of, 232-234
Lima in 1746, earthquake of, 222
Lipari Islands, volcanoes of, 69 _et seq._
Lisbon, earthquake of, 221
Lister, J. J., 38
Lunar volcanoes, 236 _et seq._
Lyell, Sir C., 30, 62, 78, 217
Mackowen, Col., 74
Magdala, volcanic series of, 192-193
Mallet, R., 9, 217
Mauna Loa, 19, 39, 249
Mica-trap, 262
Milne, Prof., 28, 218, 253
Moab, volcanic regions of, 132
Moon, volcanoes of, 236 _et seq._
Monte Nuovo, 85
Mull, 172 _et seq._
Neapolitan group of volcanoes, 28
New Zealand, volcanoes of, 146
Obsidian, 264
Ocean waves of seismic origin, 208, 220
O'Reilly, Prof., 9, 219
Orizaba, 21
Ovid, 3
Pacific, volcanic islands of, 37
Palestine, dormant volcanoes of, 126-135
Palmieri, Prof., 55
Pantelleria, 74
Phlegraean fields, 85
Phonolite, 263
Pitchstone, 264
Pliny, 2, 4
Porphyrite, 262
Powell, Major, 138
Pre-Tertiary volcanic rocks, 187 _et seq._;
of British Isles, 196 _et seq._
Puy de Dome, 105-110
Pythagoreans on volcanoes, 2-3
Quito, Cordilleras of, 25
Rangitoto, 19, 149
Reyer, Dr. E., 17
Rhine valley, volcanoes of, 113 _et seq._
Rhyolite, 263
Riviera in 1887, earthquake of, 219
Rocca Monfina, 80
Roderberg, 119, 120
Rome, 88-89
Rosenbusch, H., 260
Roto Mahana, 151
Ruapahu, 151
Russell, Hon. Rollo, 213
Rutley, F., 260
St. Helena, 37
San Francisco, Mount, 138
Santorin, 76-83
Schehallion, 10
Schumacher, 127
Scotland, volcanic districts of, 172 _et seq._
Scrope, Poulett, 5, 73, 93, 98
Scuir of Eigg, 180-184
Seismic phenomena, special, 201 _et seq._, 217 _et seq._
Shasta, Mount, 140
Siebengebirge, 116-120
Skye, 177-179
Sleamish, 168
Smyth, Piazzi, 33
Snake River, volcanoes of, 142
Staffa, 185-186
Strabo on volcanoes, 3
Stromboli, 71-73
Sumatra, volcanic action in, 226
Syenite, 262
Symes, R. G., 167
Syria, earthquakes in, 219
Taupo Lake, 150
Taylor, Mount, 138
Tell el Ahmar, 131
Tell el Akkasheh, 131
Tell el Farras, 131
Tell Abu en Neda, 130
Tell Abu Nedir, 129
Templepatrick, quarry at, 160
Teneriffe, 33
Tertiary period, volcanic activity of, 255
Thucydides, 2
Tonga Islands, volcanoes of, 38
Tongariro, 151
Trachyte, 263
Trass of Bruehl Valley, 123-125
Tristan da Cunha, 37
Tristram, Canon, 127, 131
Utah, volcanoes of, 137
Verbeek, R. D. M., 202
Vesuvius, 4, 14, 41-60, 67, 229
Volcanoes,
historic notices of, 1-5;
form, structure, and composition of, 10-19;
lines and groups of active, 20-29;
of mid-ocean, 30-40;
extinct or dormant, 84 _et seq._;
special volcanic and seismic phenomena, 201 _et seq._;
the ultimate cause of volcanic action, 225 _et seq._;
whether we are living in an epoch of special volcanic activity, 253-256;
brief account of volcanic rocks, 259-265
Vulcanists, 5
Vulcano, 69, 71
Wallace, A. R., 81
Waltershausen, W. S. von, 7, 61
Wellington, Mount, 149
Wharton, Capt., 212
Whymper, E., 18
Yarmuk, valley of the, 129, 131
Yellowstone Park, 145
Zirkel, F., 260
Zoellner, 240
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physiological and psychological problems which have not yet received
much attention in the scientific world of England."--_Nature._
X. MANUAL TRAINING. By Dr. C. M. WOODWARD, Director of the Manual
Training School, St. Louis. Illustrated.
"There is no greater authority on the subject than Professor
Woodward."--_Manchester Guardian._
XI. THE SCIENCE OF FAIRY TALES. By E. SIDNEY HARTLAND.
"Mr. Hartland's book will win the sympathy of all earnest students, both
by the knowledge it displays, and by a thorough love and appreciation of
his subject, which is evident throughout."--_Spectator._
XII. PRIMITIVE FOLK. By ELIE RECLUS.
"For an introduction to the study of the questions of property,
marriage, government, religion,--in a word, to the evolution of
society,--this little volume will be found most convenient."--_Scottish
Leader._
XIII. THE EVOLUTION OF MARRIAGE. By Professor LETOURNEAU.
"Among the distinguished French students of sociology, Professor
Letourneau has long stood in the first rank. He approaches the great
study of man free from bias and shy of generalisations. To collect,
scrutinise, and appraise facts is his chief business."--_Science._
XIV. BACTERIA AND THEIR PRODUCTS. By Dr. G. SIMS WOODHEAD. Illustrated.
"An excellent summary of the present state of knowledge of the
subject."--_Lancet._
XV. EDUCATION AND HEREDITY. By J. M. GUYAU.
"It is a sign of the value of this book that the natural impulse on
arriving at its last page is to turn again to the first, and try to
gather up and coordinate some of the many admirable truths it
presents."--_Anti-Jacobin._
XVI. THE MAN OF GENIUS. By Professor LOMBROSO. Illustrated.
"By far the most comprehensive and fascinating collection of facts and
generalisations concerning genius which has yet been brought
together."--_Journal of Mental Science._
XVII. THE GRAMMAR OF SCIENCE. By Professor KARL PEARSON. Illustrated.
XVIII. PROPERTY: ITS ORIGIN AND DEVELOPMENT. By CH. LETOURNEAU, General
Secretary to the Anthropological Society, Paris, and Professor in
the School of Anthropology, Paris.
An ethnological account of the beginnings of property among animals, of
its communistic stages among primitive races, and of its later
individualistic developments, together with a brief sketch of its
probable evolution in the future.
* * * * *
London: WALTER SCOTT, LIMITED, 24 Warwick Lane.
* * * * *
Transcriber's note:
Changed 'Kilarrea' to 'Kilauea' on page 19: Mauna Loa and Kilarrea.
Changed 'Kilanea' to 'Kilauea' on page 39: Kilanea, 4158 feet.
Made punctuation (semi-colons) consistent in caption to figure 16.
Changed 'Brionde' to 'Brioude' on page 94: till at Brionde it becomes.
Changed 'occuping' to 'occupying' on page 96: occuping a hollow.
Changed 'Rodesberg' to 'Roderberg' on page 118: old extinct volcano of
Rodesberg.
Changed 'Wolkenberg' to 'Wolkenburg' on page 118: and that of the
Wolkenberg.
Left the reference to Jeremiah, l. 25. in footnote to Part III Chapter
I, although Jeremiah, li. 25. seems more appropriate.
Changed 'fumarols' to 'fumaroles' on page 137: fumarols give evidence.
Removed extra comma on page 153: of the present, epoch.
Changed 'columnal' to 'columnar' on page 176: the columnal structure.
Changed 'groves' to 'grooves' on page 183: the groves and scorings.
Changed 'Angust' to 'August' on page 212: the 27th of Angust.
Changed 'mikroskopischen' to 'mikroskopische' on page 260: ueber
mikroskopischen Structur.
Changed 'become' to 'becomes' on page 260: the rock become a
leucite-basalt.
Left inconsistent spellings of 'Baalbec' and 'Baalbeck'; 'Harrat' and
'Harrat'; 'metres' and 'metres'; 'pitchstone' and 'pitch-stone';
'prehistoric' and 'pre-historic'; 'Rhone' and 'Rhone'; 'sub-aerial',
'subaerial' and 'subaerial'; 'tableland' and 'table-land'.
Greek words were replaced with their transliterations: 'meson pyr' and
'Peri kosmou'.
The oe-ligature was expanded to the two separate characters: 'Euboea'
and 'Boeotia'.
Left the list numbering as is at the beginning of Chapter II of Part IV,
even though the list begins at item c, as if it continues the list which
began in the previous chapter.