CONCERNING CERTAIN NATURAL PHENOMENA.—ORIGIN OF THE
DIAMOND.—FORMATION AND COLOURING OF GEMS.—INFILTRATION
OF PEBBLES.—CAUSE OF TRANSPARENCY.—INTEGRITY OF THE
FOSSIL-NODULES.—THEORY OF THE SHATTERED FLINTS.—CONCLUDING
OBSERVATIONS.
The charm which wins and rivets our attention in such pursuits as those
of Geology or Mineralogy, is not that the phenomena which we meet with
are capable of being classified, and of forming a scientific system.
All this is, no doubt, one day instructive and interesting; but it was
an afterthought, the result of experiment. The first charm lay in that
silent mystery which broods over every part of creation, a veil as yet
unpenetrated by Science: it lay in our instinctive consciousness that
Nature, in what are, perhaps, her simplest movements, still transcends
all the master-pieces of Art.
Take, for instance, the crystalline gems. These are the most remarkable
substances with which we are acquainted; they are also among the most
simple. Chemically speaking, the metals and gases may claim to be
regarded as simpler bodies; but then it must be remembered that we do not
meet with them in nature thus unmixed. Gases vary, both in volume and
character, every instant; and ordinary metallic ores are penetrated and
disguised by foreign matter; whereas faultless crystals, once perfected,
appear to be unalterable.
Some of these, as the DIAMOND, would almost seem to be an elementary
substance; and yet this can hardly be the actual case. The philosophical
account of a crystal, as “some substance, all the particles of which,
being free to move, have been operated upon in the way of a chemical,
perhaps an electrical change,” certainly makes against it; for, according
to this definition, such “substance” is a first desideratum, without
which we cannot have the “crystal.” Thus, oxygen and hydrogen, blended
together in certain definite proportions, yield the fluid substance,
WATER; and the “crystal” of water is ICE. In like manner, common white
carbonate of lime, and the fluor spars, whose ingredients we know, are
in daily process of formation.
The philosophical idea, so accurately expressed in the above definition,
is, doubtless, correct, if once we assume a past history for some
substance, and take the crystal before us as its result. But, whether all
bodies which we now meet with under the form of crystals _have, in point
of fact, had such a history_, is quite another question.
The diamond is universally held to be pure CARBON crystallized. Its high
refraction indicated this to Newton long ago; and the proof has since
been given twofold: for the diamond scales off and evaporates under
intense heat, and its dust has _carbonized_ iron-filings, turning them
into steel.
Further, this carbon is supposed to be of vegetable origin; and, if so,
it would seem to follow that there must have been plants, and perhaps
coal-strata, before there could be any diamonds.
But _what was the process_ actually carried out in nature? No one has
hitherto succeeded in obtaining this gem, answering to the conditions of
a “brilliant” in water, lustre, and weight, by any attempted method,
from the base of carbon. The French chemists have now, for some years
past, been experimenting upon _boron_, by means of the voltaic battery;
and they have, it seems, taken out of the crucible sundry small, pale
crystals, which are found to be nearly as hard as adamantine spar (a
variety of _corundum_); but they cannot show, as the fruit of their
labours, a diamond weighing one carat, and worth, according to the
tariff, eight pounds sterling in the market of Europe. Indeed, if this
boron be a mineral intermediate between carbon and silex, their gems will
assuredly partake of the character of rock-crystal, a stone which has no
affinity with the diamond whatever.
The process of Nature, therefore, being unknown, if indeed it ever took
place, the question fairly arises—whether diamond be a derived crystal,
or itself an original type of created matter. Or it might be put thus:
“If diamond be the purest form of carbon known, what is carbon then but
diamond debased?”
Neither does this exhaust the argument. The ruby owns a matrix: the pearl
grows in the mother-of-pearl. What is the nature of the diamond-rock? Is
it a dark conglomerate? or is it diaphanous?
We know how diamonds are obtained: how they are picked out of the
crevices of certain rocks, and washed out of the sands of certain
rivers—in the Carnatic, and Brazil, and Borneo; but we do not seem to be
much nearer to the history of their parentage.
Again, _what is_ their “crust” or coating with which they are always
found enveloped? Is it an integral part of the stone, or is it
adventitious? In the best diamonds this crust is of a greenish hue.
Some say that while the gem itself has _positive_ electricity, its crust
shows _negative_. If this be so, the last question is answered—the crust
in that case cannot be an integral part of the stone. The only absolute
reason I know of for concluding the diamond to be a _derived_ substance
is, that it is laminar. The Eastern lapidaries, as it is well known, will
sometimes _divide_ a stone by striking it a sharp blow in the cleavage.
After all, the most extraordinary property of the diamond, as pure
carbon, is its weight. It is fifty times the weight of refined charcoal.
How was the element of carbon condensed and inspissated thus? Was it by
the action of LIGHT? This is the vegetable analogy; as we see in the
case of all growing plants: did it hold here?
* * * * *
If we were to inquire how oriental sapphires, including the ruby, the
blue sapphire, the emerald, and the amethyst, are formed from CLAY, that
clay which exists in the granite rocks, the difficulty would be nearly as
great. We do not know at all.
But there is some satisfaction in having undoubted proof of the nature of
their “base.” And the obvious evidence upon this point is very simple,
and prior to that of chemical analysis. My own attention was first
drawn to it many years ago, in a casual remark made by a friend. We
were handling some crystals of the _white_ sapphire, a stone of little
value. “These look very like glass,” said I. “Yes, but you may always
tell them from glass by their _coldness_. Touch one with your tongue.”
Then followed the inquiry. “And why is it so much colder than glass is?”
“Because the ‘base’ of the sapphire is CLAY, and clay is a very cold
substance.”
* * * * *
Let us now pass on to consider the question of COLOUR. In the existing
varieties of gems, we have all the colours of the _spectrum_ perpetuated
and vivid.
What is the source of these colours? And how are they blended with the
solid crystal?
There seems to be no reason for doubting that the immediate source or
cause of colour is the presence of some oxidized metal. All the colours
which Nature has impressed appear, as far as we can trace them, to be
due to such a presence. Opaline tints, and those of the “cat’s eye,”
are an exception; being the perceptible result of a peculiar texture
and configuration; so also are the iridescent hues on a _soap-bubble_,
which are probably caused by polarized light. But it is _a metal_ which
makes the bark of certain trees and shrubs to glisten; aided, in the case
of the birch and wheat-stubble, by particles of silex. It is a metal,
absorbed from juices of the soil, which gives their tints to flowers, and
their deep tinge to fruits. It is a metal which dyes the plumes of the
king-fisher; and the gleaming scales of the dragon-fly and diamond-beetle
owe their brilliancy to metallic lustre. Why should this all-pervading
law vary in the crystals?
We know that metals proper affect crystalline forms, assuming them
spontaneously; and we know that the gems have come in contact with
metals. _Iron_, whose rust is of a reddish hue, enters into many of them;
and in the _red_ stones it is said to be abundant.
Probably, the finer permanent tints are due to _gold_, in infinitesimal
proportions. Professor Faraday has said that the ruby-tinted glass
called “Bohemian” derives its colour from gold in a pure form, finely
attenuated, and not from any chemical combination of that substance.
A white diamond has far more lustre than one which is yellow or
violet-tinted. But in all the sapphires, the deeper the hue, the more
brilliant and valuable the stone. Hence the technical term for the
colour of a diamond is its _water_. In all these gems the hues (whatever
their origin) are homogeneously united with the crystal; and the _modus
operandi_ of Nature is a profound secret.
* * * * *
When we descend in the mineralogical scale, and come to such stones as
agates and jaspers, the process which has been followed seems quite
capable of being traced—for its antiquity is not so great. The colours
which we now find in pebbles more or less opaque, though occasionally
lively, exist under very different conditions from those by which they
reside in the crystalline gems. It is necessary, however, to consider
first, the origin and nature of _pebbles_ as distinguished from casual
fragments of stone.
This was long held to be one of Nature’s riddles; but as soon as it was
experimentally dealt with, it met with a solution in some of its most
difficult points.
It was early decided that pebbles are _distinct formations_, complete
in themselves, except in so far as they have been worn away by gradual
attrition. The first difficulty was, how to account for the great
hardness of many of our seaside specimens. Although for the most part
inclosing an “organism,” which must have been that of some zoophyte,
they show no traces, in their present compact texture, of the soft and
yielding consistency they must at that time have possessed. The matrix
in which they lie, and from which they drop as the ripe nuts fall from a
hazel-bush, is seldom or never of so hard a substance as are the pebbles
themselves; in many cases the difference is as great as between the teeth
and gums of a living mammal.
But the evidence of the inclosed organism is conclusive as to a past
history; and in all mixed pebbles—and ninety-nine out of a hundred of
ours are mixed—it is quite certain that an _impregnation_, or an actual
_infiltration_, has taken place.
Either a fluid menstruum, usually siliceous, must have enveloped and
saturated the animal form, or there was actual injection of chalcedony
and limestone, in a soft state, into the tubes and cells of the skeleton
first, and afterwards into the pores and crevices of the new stone.
Frequently both processes have obtained. The only alternative, viz. that
which suggests that composite pebbles, revealing in their structure
distinct traces of animal or vegetable organization, _may have been_
formed thus at first, like the coloured prints in a book, I consider
to be untenable. One might as readily credit a spontaneous growth of
almond-cakes or oyster-patties by some sudden spasmodic effort of our
present sea and land.
Impregnation has, no doubt, been always going on.
A French _savant_, M. Reaumur, above a century ago, wrote as follows:—“By
a coarse operation emery is reduced to powder and suspended in water
for several days; but nature may go much further than this, for the
particles which water detaches from hard stones, by simple attrition,
are of an almost inconceivable degree of fineness. Water thus impregnated
contributes to the formation of pebbles by petrifying the stone, as it
were, a second time. Stones already formed, but having as yet a spongy
texture, acquire a flinty hardness by impregnation with this crystalline
fluid.”[3]
From such a source, as he supposes, has arisen the close texture of
Egyptian pebbles, coloured jaspers, and even agates. If he means to
include the _homogeneous_ agates, which are alike free from sparry
crystals, metallic scum, and all traces of organized matter, I do not
agree with him. But in the case of _mixed_ chalcedonic pebbles, among
which may be classed our pretty Isle of Wight specimens, no doubt such
impregnation took place, and was followed by a further process of
infiltration. For when the flint-nodules, _impregnated_ as above, were
still soft—soft enough we know they were to take delicate impressions of
the spines of the echinus—chalcedony, in a semi-fluid or viscous state,
would pass through the pores of the flint, because the former is the
finer substance of the two. And after such infiltration, the entire lump
would harden, resisting, for the most part, further change. And this
would be the pebble as we now find it.
In the “Geological Museum,” now open in Jermyn Street, there is a case
(on the first floor) where the nature of infiltration is well shown in
some jasper-agates. It will readily be seen here that each internal layer
has been formed in succession _from without_, the centre of the pebble
filling up last. In another case (labelled “Silica”), on the opposite
side of this room, are some “choanites” and “sponges” presented by the
author.
Those latter will be found worthy of ten minutes’ inspection, even as
seen through the plate of glass which serves to protect them. They are
selected, not as being the finest specimens in his cabinet, but as
illustrating, each of them, a particular animal, or a peculiar _position_
of one in the fossil state. They are, however, very good specimens,
much above the average; and if any one became missing, it could never
be exactly replaced, though you should search the world over. Nature
does not stamp the same “medal” _twice_. Any person who, after examining
these, likes to start a theory of his own to account for their forms
and colours, has my full permission to do so. But one word I would say
in friendly warning, seeing that theories do abound. The Chinese, that
ancient and wise people, have a theory that “asbestos” cloth may have
been manufactured “of the hair of certain rats that lived in the flames
of certain volcanoes.” It were monstrous to doubt it.
In my beach-rambles I have often picked up and examined globes of
sandstone which were partially chalcedonized, and that by evident
infiltration. The lapidaries call these “sand-agates,” and reject them
as unfit for the wheel; and so they are at present, but it would be
instructive to meet with some of them twenty years hence, after they had
undergone a more confirmed treatment at the hands of Dame Nature.
The well-known specimens of “petrified wood,” common on our coasts, and
occurring in some beautiful varieties of beech and acacia in the bays of
South Devon, are a further example of infiltration; but the process here
must have been somewhat different.
The presence of metallic particles, what lapidaries term the “moss,” in
many of our agates, argues an impregnating fluid, thoroughly charged with
mineral matter. In most cases this fluid was a ferruginous stream, such
as may often be seen issuing from some hidden reservoir, and trickling
down the face of a cliff of gault or greensand. This tinges everything
that lies in its path with an indelible red stain; it then oozes on
through the shingle, and reaches the verge of the sand. The nearest pool
becomes saturated between tides, and the suspended crystals of salt,
which are of a penetrating character (as the state of your beaching-boots
will soon inform you), enter into chemical combination with the metallic
rust, and help to conduct its particles into the heart of many a
limestone pebble.
Dark inland pebbles, on the other hand, will discharge much of the oxide
which they have imbibed, and may be observed to brighten and improve
their complexions after a few months’ sponging and tossing in the purer
sea-water.
Some of our handsomer pebbles, when cut in two, reveal blotches of metal,
which are glossy after polishing on the wheel. This metal is occasionally
native iron. The darker varieties of “moss” contain a good deal of
manganese, and some silver.
From what has been said about impregnation, we may readily conclude
that the _colours_ found in our agate-pebbles have been chemically
inwrought, and that the symmetrical _patterns_, over which these
colours are disposed, are not due to a succession of “layers,” as in
the ribbon-jaspers and Scotch pebbles, but must be referred to the
organization of some extinct zoophyte, whose skeleton is preserved in the
existing fossil.
The cause of translucency, or even _transparency_, in some pebbles is, no
doubt, to be sought in their finer and more even texture, but especially
in the latter quality. Sir Isaac Newton was of opinion that the opacity
of certain substances is simply a result of their cross-grained
composition. He held that in a transparent body the particles must be
regularly and evenly disposed at equal intervals, so that a ray of light
entering such a substance would pass steadily on, according to the known
laws of gravity and motion, meeting with no obstruction beyond that of
the homogeneous density of the medium which it had to traverse. Whereas,
in opaque bodies, he supposes these constituent particles to be unevenly
disposed, and that the ray which enters at the surface is, as it were,
pushed about and thrust aside, and at length lost to sight.
The purity of spring-water, when undisturbed, illustrates this beautiful
theory of the great philosopher; and, among solid substances, good
glass, especially plate-glass which, after fusing in the furnace, has
been carefully run and settled in the frames. It may also be simply shown
in the act of wetting or steeping certain dry substances. Thus, stout
writing-paper, owing to its cross texture, is opaque when dry; but if we
immerse a sheet of it in oil, and then hold it up to the light, we find
it has become transparent. For the smooth medium thus imbibed has entered
its pores, and _equalized_ the general texture.
We find also a striking argument for the probable truth of Newton’s
eagle-eyed conclusion in certain minerals which possess double refraction.
ICELAND SPAR, one of these, is perhaps the most perfectly transparent
solid with which we are acquainted. Now, Iceland Spar _transmits_ both
the rays, as we see in the twofold image which is presented to us. But
TOURMALINE is opaque, even the red specimens looking almost black; and
we find that Tourmaline _absorbs_ one of the two rays of polarized
light. This singular stone polarizes a beam of light if it enter in any
direction but that of the longer axis.
No solid with which we are acquainted is absolutely transparent. And
there is no perfect _reflector_ known. The best-polished surface
_absorbs nearly one-half_ of that quantity of light which strikes upon it.
As to our seaside pebbles, the most compact of them are even _visibly_
porous. Cut through the hardest jasper, and polish one face till it
shines like a steel mirror, and then hold it so as to reflect the light,
you will at once discern numerous minute specks or flaws on this surface,
as if the point of a needle or graving-tool had been busily at work upon
it. These specks have always been there. They are _air-holes_, and in the
case of a fossil-pebble were, some of them, doubtless, connected with the
position which the animal occupied just before he died. These air-holes
must have traversed this hard stone in every direction, for, cut the
pebble how you will, you meet with them. Others again, incomparably
more numerous, but which can scarcely be discerned without the aid of a
powerful microscope, are the true _pores_ belonging to this apparently
impenetrable substance.
I have found that the action of daylight tells even upon polished agates
after a time. Some of the spots and markings in the finest stones grow
fainter in the course of many years. Others appear to deepen. This is, no
doubt, a change resulting from the oxygen, contained in a beam of light,
acting readily upon carbon, silex, and other substances. And it furnishes
an independent argument for concluding that the visible beauty of these
formations, in perpetuating a coloured pattern, has been due rather to
mixed _chemical_ processes than to pure crystallography.
The fossil nodules, mostly siliceous, which we find upon a sea-beach, are
_integral_ specimens. It never but once happened to me to meet with what
appeared to be _two_ choanites in the same pebble, and I incline now to
believe that this was in fact _one_ choanite who had _divided_ himself
after the manner of the Luidia. But even supposing that here were,
indeed, a pair of perfect animals, when it is considered that this was
one single instance, occurring among more than a thousand picked up by
me, in which the choanites were always solitary, such an exception may be
almost said to prove the rule.
The late lamented Hugh Miller has stated the like fact concerning his
Morayshire and Cromarty icthyolites. At pp. 194, 195, of his “Cruise of
the Betsy,” he remarks that “the limestone nodules take very generally
the _form_ of the fish which they inclose; they are stone coffins
carefully moulded to express the outline of the corpses lying within.”
Then, after observing that the shape of the stone conforms to the
attitude of the fish in every instance, he goes on to state that “the
_size_ of the fish regulates that of the nodule. The coffin is generally
as good a fit in size as in form; and the bulk of the nodule bears almost
always a definite proportion to the amount of animal round which it had
formed.”
He then gives, in his usual clear and graphic language, the following
remarkable statement, the result of direct experiment.
“When a calcareous earth, mixed up with sand, clay, and other extraneous
matters, was deposited on some of the commoner molluscs of our shores,
it was universally found that the mass, incoherent everywhere else,
had acquired a solidity wherever it had been penetrated by the animal
matter of the molluscs. Each animal, in proportion to its size, was found
to retain, as in the fossiliferous spindles of the Old Red Sandstone,
its coherent nodule around it. Here the animal matter gave solidity to
the lime in contact with it. But in the _natural_ phenomenon of the
icthyolite beds, there was yet a further point, for in these the animal
matter must have possessed such _an affinity_ for the mineral, as to
form, in an argillaceous compound, a centre of attraction powerful
enough to draw together the lime diffused throughout the mass.”
Hugh Miller concludes the above passage by saying that “it still remains
for the geologic chemist to discover on what principle masses of animal
matter should form the attracting nuclei of limestone nodules.”
Upon which last remark, I would suggest that the principle of the “law
of definite proportions,” established by Dalton, and fully borne out
by all succeeding experiments in chemistry, appears to meet the case,
geologically as well as chemically, in every respect. For such a law must
of course obtain, whether the chemical ingredients be present in the
forms of mineral, vegetable, or animal life; in fact, we have never known
the law to vary. It holds for the compounded elements which we term AIR
and WATER; it holds for the crystals; it holds for vascular and cellular
tissues; why should it fail when the further instance of a mollusc or a
zoophyte is in question?
I see no reason to doubt that the blood, muscle, membrane, or adipose
matter of any animal have their due respective affinities for the
different substances of the mineral creation.
No doubt, however, electricity, as an active cause, bears directly upon
all such phenomena.
I remember many years since being greatly perplexed with the _discovery_
(as I then thought it) that in certain parts of the Isle of Wight, and
along the Dorsetshire coast, the rows of dark flints imbedded in the
upper chalk of the cliff-ranges were all _broken_; broken _small_, so
that if one were taken out of its chalk socket it crumbled in your hand.
Often and often, I turned this fact over in my mind, and sought some
apparent way to account for it. But I think I now see one way to account
for it; and which may perhaps be judged worthy of acceptance, until a
better solution is hit upon. In Dr. Hook’s experiment with that once
common household implement, the “flint and steel,” he found that the
_sparks_ which “fly” upon collision taking place are minute spherules of
metal. And further, that this metal was now not _steel_ any longer, but
iron; the fragments struck off _having lost their polarity_ in the moment
of contact with the flint.
This experiment shows that silex possesses some remarkable affinity for
the magnetic fluid, since in this case it had robbed the steel of it,
for those spherules would not answer to the magnet. May not, therefore,
the rows of flints in the cliff have attracted the lightning in severe
thunderstorms, and been shivered by the blow? This would not necessarily
hurl the chalk down.
* * * * *
The Arabs have a proverb which says, “Under the lamp it is dark.”
Certainly, the chief mystery of every animated creature seems to reside
_in its life_, and _Life_ is like a burning lamp. Once the life extinct,
we can anatomize and analyze, and arrive at many partial conclusions;
but, meanwhile, the life has departed, and we do not know what that was.
The nearest thing to its likeness is _expression_; and animals rank high
in the scale of being, according as they command and impart expression.
A dog or horse have a great deal; a bird some; a reptile or insect,
absolutely none to our eyes.
With these latter, however, their _habits_, while alive, take the
place of any more intelligent expression; especially some of their
more excited movements. We know by the _sound_, when a snake is angry;
and as to motion, the attack of a provoked hornet is a startling thing
to witness. Ordinarily speaking, however, all their habits tend to
concealment; no doubt, for the sake of safety. I believe no one ever
sees the Sphynx-moth, called a “Death’s-head” (_Acherontia Atropos_), on
the wing. Yet we discern many others which, like it, fly in the hours of
dusk. But this insect whirls through the air like a stone from a sling.
It has never yet, in my experience as a naturalist, been my lot to meet
with the burrowing insect called an Ant-lion. Only twice in my life have
I encountered a slow-worm in the woods of Devon and the Isle of Wight.
And to instance the case of a far commoner creature, how seldom does it
happen to any one to take the large dragon-fly behind his green leaf!
* * * * *
And yet the problems of inanimate matter are perhaps the most difficult
to solve. They have deeply exercised philosophers in every age of the
world.
“All things considered,” says Newton, “I think it probable that God,
in the beginning, formed matter in solid, hard, impenetrable, movable
particles; of such sizes and figures, and with such other properties
as most conduced to the end for which He formed them. And that these
primitive particles, being solids, are incomparably harder than any of
the sensible porous bodies compounded of them; even so hard as never to
wear, or break in pieces; no other power being able to divide what God
made one in the first Creation. While these corpuscles remain entire,
they may compose bodies of one and the same matter and texture in all
ages; but should they wear away or break in pieces, the nature of things
depending on them would be changed. Water and earth composed of old worn
particles and fragments of particles, would not be of the same nature
and texture now with water and earth composed of entire particles at the
beginning. And therefore, that Nature may be lasting, the changes of
corporeal things are to be placed only in the various separations and new
associations of these permanent corpuscles.”
So wrote the man, “Qui genus humanum ingenio superavit,” who at the age
of twenty-four had already invented the Fluxional Calculus, discovered
the Decomposition of Light, and enunciated and proved, in a series of
lemmas, the law of Universal Gravitation.
* * * * *
But soft! What is this which steals upon our senses through bobbing
apple-blossoms at the open casement? It is the delicious, oystery smell
of the Sea, as the afternoon tide runs in with a sound like that of
fairy-bells upon the sand and rock and loose shingle.
That scent, and sight, and sound, are altogether irresistible. We throw
aside Dr. Buckland and Hugh Miller, clap on a “wide-awake,” rush down
at once by the zig-zag path, and madly catch up a bunch of dripping
tangle, and kick a hole in the moist sand, and presently find that our
“Balmorals” are ancle-deep in the brine of a nimble wave.
And now I descry a faint purplish hue upon the red beach which lies at
the foot of Culver. To-morrow, we will breakfast early, and hunt up a
score of pebbles before the day grows hot.
[3] “Mémoires de l’Académie des Sciences.” Anno, 1721.