Working Lecture in Schoolroom.
L. We have been hitherto talking, children, as if crystals might
live, and play, and quarrel, and behave ill or well, according to
their characters, without interruption from anything else. But so
far from this being so, nearly all crystals, whatever their
characters, have to live a hard life of it, and meet with many
misfortunes. If we could see far enough, we should find, indeed,
that, at the root, all their vices were misfortunes: but to-day I
want you to see what sort of troubles the best crystals have to go
through, occasionally, by no fault of their own.
This black thing, which is one of the prettiest of the very few
pretty black things in the world, is called "Tourmaline." It may
be transparent, and green, or red, as well as black; and then no
stone can be prettier (only, all the light that gets into it, I
believe, comes out a good deal the worse; and is not itself again
for a long while). But this is the commonest state of it,--opaque,
and as black as jet.
MARY. What does "Tourmaline" mean?
L. They say it is Ceylanese, and I don't know Ceylanese, but we
may always be thankful for a graceful word, whatever it means
MARY. And what is it made of?
L. A little of everything there's always flint and clay, and
magnesia in it, and the black is iron, according to its fancy, and
there's boracic acid if you know what that is and if you don't, I
cannot tell you today, and it doesn't signify and there's potash,
and soda, and, on the whole, the chemistry of it is more like a
mediaeval doctor's prescription, than the making of a respectable
mineral but it may, perhaps, be owing to the strange complexity of
its make, that it has a notable habit which makes it, to me one of
the most interesting of minerals. You see these two crystals are
broken right across, in many places, just as if they had been
shafts of black marble fallen from a ruinous temple, and here they
lie, imbedded in white quartz, fragment succeeding fragment
keeping the line of the original crystal, while the quartz fills
up the intervening spaces Now tourmaline has a trick of doing
this, more than any other mineral I know here is another bit which
I picked up on the glacier of Macugnaga; it is broken, like a
pillar built of very flat broad stones, into about thirty joints,
and all these are heaved and warped away from each other sideways,
almost into a line of steps, and then all is tilled up with quartz
paste. And here, lastly is a green Indian piece, in which the
pillar is first disjointed, and then wrung round into the shape of
an S.
MARY. How CAN this have been done?
L. There are a thousand ways in which it may have been done, the
difficulty is not to account for the doing of it, but for the
showing of it in some crystals and not in others You never by any
chance get a quartz crystal broken or twisted in this way. If it
break or twist at all which it does sometimes, like the spire of
Dijon, it is by its own will or fault, it never seems to have been
passively crushed But, for the forces which cause this passive
ruin of the tourmaline,--here is a stone which will show you
multitudes of them in operation at once It is known as "biecciated
agate," beautiful, as you see, and highly valued as a pebble yet,
so far as I can read or hear no one has ever looked at it with the
least attention At the first glance, you see it is made of very
fine red striped agates, which have been broken into small pieces,
and fastened together again by paste also of agate There would be
nothing wonderful in this, if this were all. It is well known that
by the movements of strata, portions of rock are often shattered
to pieces:--well known also that agate is a deposit of flint by
water under certain conditions of heat and pressure: there is,
therefore, nothing wonderful in an agate's being broken; and
nothing wonderful in its being mended with the solution out of
which it was itself originally congealed. And with this
explanation, most people, looking at a brecciated agate, or
brecciated anything, seem to be satisfied. I was so myself, for
twenty years; but, lately happening to stay for some time at the
Swiss Baden, where the beach of the Limmat is almost wholly
composed of brecciated limestones, I began to examine them
thoughtfully; and perceived, in the end, that they were, one and
all, knots of as rich mystery as any poor little human brain was
ever lost in. That piece of agate in your hand, Mary, will show
you many of the common phenomena of breccias; but you need not
knit your brows over it in that way; depend upon it, neither you
nor I shall ever know anything about the way it was made, as long
as we live.
DORA. That does not seem much to depend upon.
L. Pardon me, puss. When once we gain some real notion of the
extent and unconquerableness of our ignorance, it is a very broad
and restful thing to depend upon: you can throw yourself upon it
at ease, as on a cloud, to feast with the gods. You do not
thenceforward trouble yourself,--nor any one else,--with theories,
or the contradiction of theories; you neither get headache nor
heart-burning and you nevermore waste your poor little store of
strength or allowance of time.
However, there are certain facts, about this agate-making, which I
can tell you; and then you may look at it in a pleasant wonder as
long as you like, pleasant wonder is no loss of time.
First, then, it is not broken freely by a blow; it is slowly
wrung, or ground, to pieces. You can only with extreme dimness
conceive the force exerted on mountains in transitional states of
movement. You have all read a little geology; and you know how
coolly geologists talk of mountains being raised or depressed.
They talk coolly of it, because they are accustomed to the fact;
but the very universality of the fact prevents us from ever
conceiving distinctly the conditions of force involved. You know I
was living last year in Savoy; my house was on the back of a
sloping mountain, which rose gradually for two miles behind it;
and then fell at once in a great precipice toward Geneva, going
down three thousand feet in four or five cliffs, or steps. Now
that whole group of cliffs had simply been torn away by sheer
strength from the rocks below, as if the whole mass had been as
soft as biscuit. Put four or five captains' biscuits on the floor,
on the top of one another; and try to break them all in half, not
by bending, but by holding one half down, and tearing the other
halves straight up;--of course you will not be able to do it, but
you will feel and comprehend the sort of force needed. Then, fancy
each captains' biscuit a bed of rock, six or seven hundred feet
thick; and the whole mass torn straight through; and one half
heaved up three thousand feet, grinding against the other as it
rose,--and you will have some idea of the making of the Mont
Saleve.
MAY. But it must crush the rocks all to dust!
L. No; for there is no room for dust. The pressure is too great;
probably the heat developed also so great that the rock is made
partly ductile; but the worst of it is, that we never can see
these parts of mountains in the state they were left in at the
time of their elevation; for it is precisely in these rents and
dislocations that the crystalline power principally exerts itself.
It is essentially a styptic power, and wherever the earth is torn,
it heals and binds; nay, the torture and grieving of the earth
seem necessary to bring out its full energy; for you only find the
crystalline living power fully in action, where the rents and
faults are deep and many.
DORA. If you please, sir,--would you tell us--what are "faults"?