serve to throw any light upon the tales of the quarryman. The first
point to which attention may be directed is that involved in the
statement that the amphibian has been imprisoned in a _solid_ rock.
Much stress is usually laid on the fact that the rock was solid; this
fact being held to imply the great age, not to say antiquity, of the
rock and its supposed tenant. The impartial observer, after an
examination of the evidence presented, will be inclined to doubt
greatly the justification for inserting the adjective "solid"; for
usually no evidence whatever is forthcoming as to the state of the
rock prior to its removal. No previous examination of the rock is or
can be made, from the circumstance that no interest can possibly
attach to its condition until its removal reveals the apparent wonder
it contained, in the shape of the live toad. And it is equally
important to note that we rarely, if ever, find mention of any
examination of the rock being made subsequently to the discovery.
Hence, a first and grave objection may be taken to the validity of the
supposition that the rock was solid, and it may be fairly urged that
on this supposition the whole question turns and depends. For if the
rock cannot be proved to have been impermeable to and barred against
the entrance of living creatures, the objector may proceed to show the
possibility of the toad having gained admission, under certain notable
circumstances, to its prison-house.
The frog or toad in its young state, and having just entered upon its
terrestrial life, is a small creature, which could, with the utmost
ease, wriggle into crevices and crannies of a size which would almost
preclude such apertures being noticed at all. Gaining access to a
roomier crevice or nook within, and finding there a due supply of air,
along with a dietary consisting chiefly of insects, the animal would
grow with tolerable rapidity, and would increase to such an extent
that egress through its aperture of entrance would become an
impossibility. Next, let us suppose that the toleration of the toad's
system to starvation and to a limited supply of air is taken into
account, together with the fact that these creatures will hibernate
during each winter, and thus economize, as it were, their vital
activity and strength; and after the animal has thus existed for a
year or two--no doubt under singularly hard conditions--let us imagine
that the rock is split up by the wedge and lever of the excavator. We
can then readily enough account for the apparently inexplicable story
of "the toad in the rock." "There is the toad and here is the solid
rock," say the gossips. "There is an animal which has singular powers
of sustaining life under untoward conditions, and which, in its young
state, could have gained admittance to the rock through a mere
crevice," says the naturalist in reply. Doubtless, the great army of
the unconvinced may still believe in the tale as told them; for the
weighing of evidence and the placing _pros_ and _cons_ in fair
contrast are not tasks of congenial or wonted kind in the ordinary run
of life. Some people there will be who will believe in the original
solid rock and its toad, despite the assertion of the geologists that
the earliest fossils of toads appear in almost the last-formed rocks,
and that a live toad in rocks of very ancient age--presuming,
according to the popular belief, that the animal was enclosed when the
rock was formed--would be as great an anomaly and wonder as the
mention, as an historical fact, of an express train or the telegraph
in the days of the patriarchs. In other words, the live toad which
hops out of an Old Red Sandstone rock must be presumed, on the popular
belief, to be older by untold ages than the oldest fossil frogs and
toads. The reasonable mind, however, will ponder and consider each
feature of the case, and will rather prefer to countenance a
supposition based on ordinary experience, than an explanation brought
ready-made from the domain of the miraculous; whilst not the least
noteworthy feature of these cases is that included in the remark of
Smellie, respecting the tendency of uneducated and superstitious
persons to magnify what is uncommon, and in his sage conclusion that
as a rule such persons in the matter of their relations "are not to be
trusted."
But it must also be noted that we possess valuable evidence of a
positive and direct kind bearing on the duration of life in toads
under adverse circumstances. As this evidence tells most powerfully
against the supposition that the existence of those creatures can be
indefinitely prolonged, it forms of itself a veritable court of appeal
in the cases under discussion. The late Dr. Buckland, curious to learn
the exact extent of the vitality of the toad, caused, in the year
1825, two large blocks of stone to be prepared. One of the blocks was
taken from the oölite limestone, and in this first stone twelve cells
were excavated. Each cell was one foot deep and five inches in
diameter. The mouth of each cell was grooved so as to admit of two
covers being placed over the aperture; the first or lower cover being
of glass, and the upper one of slate. Both covers were so adapted that
they could be firmly luted down with clay or putty; the object of this
double protection being that the slate cover could be raised so as to
inspect the contained object through the closed glass cover without
admitting air. In the second or sandstone block, a series of twelve
cells was also excavated; these latter cells being, however, of
smaller size than those of the limestone block, each cell being only
six inches in depth by five inches in diameter. These cells were
likewise fitted with double covers.
On November 26th, 1825, a live toad--kept for some time previously to
insure its being healthy--was placed in each of the twenty-four cells.
The largest specimen weighed 1185 grains, and the smallest 115 grains.
The stones and the immured toads were buried on the day mentioned,
three feet deep, in Dr. Buckland's garden. There they lay until
December 10th, 1826, when they were disinterred and their tenants
examined. All the toads in the smaller cells of the sandstone block
were dead, and from the progress of decomposition it was inferred that
they had succumbed long before the date of disinterment. The majority
of the toads in the limestone block were alive, and, curiously enough,
one or two had actually increased in weight. Thus, No. 5, which at the
commencement of its captivity had weighed 1185 grains, had increased
to 1265 grains; but the glass cover of No. 5's cell was found to be
cracked. Insects and air must therefore have obtained admittance and
have afforded nourishment to the imprisoned toad; this supposition
being rendered the more likely by the discovery that in one of the
cells, the covers of which were also cracked and the tenant of which
was dead, numerous insects were found. No. 9, weighing originally 988
grains, had increased during its incarceration to 1116 grains; but
No. 1, which in the year 1825 had weighed 924 grains, was found in
December, 1826, to have decreased to 698 grains; and No. 11,
originally weighing 936 grains, had likewise disagreed with the
imprisonment, weighing only 652 grains when examined in 1826.
At the period when the blocks of stone were thus prepared, four toads
were pinned up in holes five inches deep and three inches in diameter,
cut in the stem of an apple-tree; the holes being firmly plugged with
tightly fitting wooden plugs. These four toads were found to be dead
when examined along with the others in 1826; and of four others
enclosed in basins made of plaster of Paris, and which were also
buried in Dr. Buckland's garden, two were found to be dead at the end
of a year, their comrades being alive, but looking starved and meagre.
The toads which were found alive in the limestone block in December,
1826, were again immured and buried, but were found to be dead,
without leaving a single survivor, at the end of the second year of
their imprisonment.
These experiments may fairly be said to prove two points. They firstly
show that under circumstances even of a favorable kind when compared
with the condition popularly believed in--namely, that of being
enclosed in a _solid_ rock--the limit of the toad's life may be
assumed to be within two years; this period being no doubt capable of
being extended when the animal gains a slight advantage, exemplified
by the admission of air and insect-food. Secondly, we may reasonably
argue that these experiments show that toads when rigorously treated,
like other animals, become starved and meagre, and by no means
resemble the lively, well-fed animals reported as having emerged from
an imprisonment extending, in popular estimation, through periods of
inconceivable duration.
These tales are, in short, as devoid of actual foundation as are the
modern beliefs in the venomous properties of the toad, or the ancient
beliefs in the occult and mystic powers of various parts of its frame
when used in incantations. Shakespeare, whilst attributing to the toad
venomous qualities, has yet immortalized it in his famous simile by
crediting it with the possession of a "precious jewel." But even in
the latter case the animal gets but scant justice; for science strips
it of its poetical reputation, and in this, as in other respects,
shows it, despite fable and myth, to be zoölogically an interesting,
but otherwise a commonplace member of the animal series.
[Illustration]
ON A PIECE OF CHALK
_A LECTURE TO WORKING MEN_.
(Delivered in England.)
BY T.H. HUXLEY.
[Illustration: A CHALK CLIFF.]
If a well were to be sunk at our feet in the midst of the city of
Norwich, the diggers would very soon find themselves at work in that
white substance almost too soft to be called rock, with which we are
all familiar as "chalk."
Not only here, but over the whole county of Norfolk, the well-sinker
might carry his shaft down many hundred feet without coming to the end
of the chalk; and, on the sea-coast, where the waves have pared away
the face of the land which breasts them, the scarped faces of the high
cliffs are often wholly formed of the same material. Northward, the
chalk may be followed as far as Yorkshire; on the south coast it
appears abruptly in the picturesque western bays of Dorset, and breaks
into the Needles of the Isle of Wight; while on the shores of Kent it
supplies that long line of white cliffs to which England owes her name
of Albion.
Were the thin soil which covers it all washed away, a curved band of
white chalk, here broader, and there narrower, might be followed
diagonally across England from Lulworth in Dorset, to Flamborough Head
in Yorkshire--a distance of over two hundred and eighty miles as the
crow flies.
From this band to the North Sea, on the east, and the Channel, on the
south, the chalk is largely hidden by other deposits; but, except in
the Weald of Kent and Sussex, it enters into the very foundation of
all the south-eastern counties.
Attaining, as it does in some places, a thickness of more than a
thousand feet, the English chalk must be admitted to be a mass of
considerable magnitude. Nevertheless, it covers but an insignificant
portion of the whole area occupied by the chalk formation of the
globe, which has precisely the same general character as ours, and is
found in detached patches, some less, and others more extensive, than
the English.
Chalk occurs in north-west Ireland; it stretches over a large part of
France--the chalk which underlies Paris being, in fact, a continuation
of that of the London basin; it runs through Denmark and Central
Europe, and extends southward to North Africa; while eastward, it
appears in the Crimea and in Syria, and may be traced as far as the
shores of the Sea of Aral, in Central Asia.
If all the points at which true chalk occurs were circumscribed, they
would lie within an irregular oval about three thousand miles in long
diameter--the area of which would be as great as that of Europe, and
would many times exceed that of the largest existing inland sea--the
Mediterranean.
Thus the chalk is no unimportant element in the masonry of the earth's
crust, and it impresses a peculiar stamp, varying with the conditions
to which it is exposed, on the scenery of the districts in which it
occurs. The undulating downs and rounded coombs, covered with
sweet-grassed turf, of our inland chalk country, have a peacefully
domestic and mutton-suggesting prettiness, but can hardly be called
either grand or beautiful. But on our southern coasts, the wall-sided
cliffs, many hundred feet high, with vast needles and pinnacles
standing out in the sea, sharp and solitary enough to serve as perches
for the wary cormorant, confer a wonderful beauty and grandeur upon
the chalk headlands. And in the East, chalk has its share in the
formation of some of the most venerable of mountain ranges, such as
the Lebanon.
* * * * *
What is this wide-spread component of the surface of the earth? and
whence did it come?
You may think this no very hopeful inquiry. You may not unnaturally
suppose that the attempt to solve such problems as these can lead to
no result, save that of entangling the inquirer in vague speculations,
incapable of refutation and of verification.
If such were really the case, I should have selected some other
subject than a "piece of chalk" for my discourse. But, in truth,
after much deliberation, I have been unable to think of any topic
which would so well enable me to lead you to see how solid is the
foundation upon which some of the most startling conclusions of
physical science rest.
A great chapter of the history of the world is written in the chalk.
Few passages in the history of man can be supported by such an
overwhelming mass of direct and indirect evidence as that which
testifies to the truth of the fragment of the history of the globe,
which I hope to enable you to read, with your own eyes, to-night.
[Illustration: MICROSCOPIC SECTION OF CHALK.
(Magnified nearly 300 times.)
1. Textularia. 2. Globigerina. 3. Rotalia. 4. Coccoliths.]
Let me add, that few chapters of human history have a more profound
significance for ourselves. I weigh my words well when I assert, that
the man who should know the true history of the bit of chalk which
every carpenter carries about in his breeches' pocket, though ignorant
of all other history, is likely, if he will think his knowledge out to
its ultimate results, to have a truer, and therefore a better,
conception of this wonderful universe, and of man's relation to it,
than the most learned student who is deep-read in the records of
humanity and ignorant of those of nature.
The language of the chalk is not hard to learn, not nearly so hard as
Latin, if you only want to get at the broad features of the story it
has to tell; and I propose that we now set to work to spell that story
out together.
We all know that if we "burn" chalk, the result is quicklime. Chalk,
in fact, is a compound of carbonic acid gas and lime; and when you
make it very hot, the carbonic acid flies away and the lime is left.
By this method of procedure we see the lime, but we do not see the
carbonic acid. If, on the other hand, you were to powder a little
chalk and drop it into a good deal of strong vinegar, there would be a
great bubbling and fizzing, and, finally, a clear liquid, in which no
sign of chalk would appear. Here you see the carbonic acid in the
bubbles; the lime, dissolved in the vinegar, vanishes from sight.
There are a great many other ways of showing that chalk is essentially
nothing but carbonic acid and quicklime. Chemists enunciate the result
of all the experiments which prove this, by stating that chalk is
almost wholly composed of "carbonate of lime."
It is desirable for us to start from the knowledge of this fact,
though it may not seem to help us very far toward what we seek. For
carbonate of lime is a widely-spread substance, and is met with under
very various conditions. All sorts of limestones are composed of more
or less pure carbonate of lime. The crust which is often deposited by
waters which have drained through limestone rocks, in the form of what
are called stalagmites and stalactites, is carbonate of lime. Or, to
take a more familiar example, the fur on the inside of a tea-kettle is
carbonate of lime; and, for anything chemistry tells us to the
contrary, the chalk might be a kind of gigantic fur upon the bottom of
the earth-kettle, which is kept pretty hot below.
Let us try another method of making the chalk tell us its own history.
To the unassisted eye chalk looks simply like a very loose and open
kind of stone. But it is possible to grind a slice of chalk down so
thin that you can see through it--until it is thin enough, in fact, to
be examined with any magnifying power that may be thought desirable. A
thin slice of the fur of a kettle might be made in the same way. If it
were examined microscopically, it would show itself to be a more or
less distinctly laminated mineral substance, and nothing more.
But the slice of chalk presents a totally different appearance when
placed under the microscope. The general mass of it is made up of very
minute granules; but, imbedded in this matrix, are innumerable bodies,
some smaller and some larger, but, on a rough average, not more than a
hundredth of an inch in diameter, having a well-defined shape and
structure. A cubic inch of some specimens of chalk may contain
hundreds of thousands of these bodies, compacted together with
incalculable millions of the granules.
[Illustration: CHALK.
(Magnified nearly 100 diameters.)]
The examination of a transparent slice gives a good notion of the
manner in which the components of the chalk are arranged, and of
their relative proportions. But, by rubbing up some chalk with a brush
in water and then pouring off the milky fluid, so as to obtain
sediments of different degrees of fineness, the granules and the
minute rounded bodies may be pretty well separated from one another,
and submitted to microscopic examination, either as opaque or as
transparent objects. By combining the views obtained in these various
methods, each of the rounded bodies may be proved to be a
beautifully-constructed calcareous fabric, made up of a number of
chambers, communicating freely with one another. The chambered bodies
are of various forms. One of the commonest is something like a
badly-grown raspberry, being formed of a number of nearly globular
chambers of different sizes congregated together. It is called
Globigerina, and some specimens of chalk consist of little else than
Globigerinæ and granules.
[Illustration: GLOBIGERINA.]
Let us fix our attention upon the Globigerina. It is the spoor of the
game we are tracking. If we can learn what it is and what are the
conditions of its existence, we shall see our way to the origin and
past history of the chalk.
A suggestion which may naturally enough present itself is, that these
curious bodies are the result of some process of aggregation which has
taken place in the carbonate of lime; that, just as in winter, the
rime on our windows simulates the most delicate and elegantly
arborescent foliage--proving that the mere mineral matter may, under
certain conditions, assume the outward form of organic bodies--so this
mineral substance, carbonate of lime, hidden away in the bowels of
the earth, has taken the shape of these chambered bodies. I am not
raising a merely fanciful and unreal objection. Very learned men, in
former days, have even entertained the notion that all the formed
things found in rocks are of this nature; and if no such conception is
at present held to be admissible, it is because long and varied
experience has now shown that mineral matter never does assume the
form and structure we find in fossils. If anyone were to try to
persuade you that an oyster-shell (which is also chiefly composed of
carbonate of lime) had crystallized out of sea-water, I suppose you
would laugh at the absurdity. Your laughter would be justified by the
fact that all experience tends to show that oyster-shells are formed
by the agency of oysters, and in no other way. And if there were no
better reasons, we should be justified, on like grounds, in believing
that Globigerina is not the product of anything but vital activity.
Happily, however, better evidence in proof of the organic nature of
the Globigerinæ than that of analogy is forthcoming. It so happens
that calcareous skeletons, exactly similar to the Globigerinæ of the
chalk, are being formed, at the present moment, by minute living
creatures, which flourish in multitudes, literally more numerous than
the sands of the sea-shore, over a large extent of that part of the
earth's surface which is covered by the ocean.
The history of the discovery of these living Globigerinæ, and of the
part which they play in rock-building, is singular enough. It is a
discovery which, like others of no less scientific importance, has
arisen, incidentally, out of work devoted to very different and
exceedingly practical interests.
When men first took to the sea, they speedily learned to look out for
shoals and rocks; and the more the burthen of their ships increased,
the more imperatively necessary it became for sailors to ascertain
with precision the depth of the waters they traversed. Out of this
necessity grew the use of the lead and sounding-line; and, ultimately,
marine-surveying, which is the recording of the form of coasts and of
the depth of the sea, as ascertained by the sounding-lead, upon
charts.
At the same time, it became desirable to ascertain and to indicate the
nature of the sea-bottom, since this circumstance greatly affects its
goodness as holding ground for anchors. Some ingenious tar, whose name
deserves a better fate than the oblivion into which it has fallen,
attained this object by "arming" the bottom of the lead with a lump of
grease, to which more or less of the sand or mud, or broken shells, as
the case might be, adhered, and was brought to the surface. But,
however well adapted such an apparatus might be for rough nautical
purposes, scientific accuracy could not be expected from the armed
lead, and to remedy its defects (especially when applied to sounding
in great depths) Lieutenant Brooke, of the American Navy, some years
ago invented a most ingenious machine, by which a considerable portion
of the superficial layer of the sea-bottom can be scooped out and
brought up, from any depth to which the lead descends.
In 1853, Lieutenant Brooke obtained mud from the bottom of the North
Atlantic, between Newfoundland and the Azores, at a depth of more than
ten thousand feet, or two miles, by the help of this sounding
apparatus. The specimens were sent for examination to Ehrenberg of
Berlin, and to Bailey of West Point, and those able microscopists
found that this deep-sea mud was almost entirely composed of the
skeletons of living organisms--the greater proportion of these being
just like the Globigerinæ already known to occur in chalk.
Thus far, the work had been carried on simply in the interests of
science, but Lieutenant Brooke's method of sounding acquired a high
commercial value, when the enterprise of laying down the
telegraph-cable between this country and the United States was
undertaken. For it became a matter of immense importance to know, not
only the depth of the sea over the whole line, along which the cable
was to be laid, but the exact nature of the bottom, so as to guard
against chances of cutting or fraying the strands of that costly rope.
The Admiralty consequently ordered Captain Dayman, an old friend and
shipmate of mine, to ascertain the depth over the whole line of the
cable, and to bring back specimens of the bottom. In former days, such
a command as this might have sounded very much like one of the
impossible things which the young prince in the Fairy Tales is ordered
to do before he can obtain the hand of the princess. However, in the
months of June and July, 1857, my friend performed the task assigned
to him with great expedition and precision, without, so far as I know,
having met with any reward of that kind. The specimens of Atlantic mud
which he procured were sent to me to be examined and reported upon.
The result of all these operations is, that we know the contours and
the nature of the surface-soil covered by the North Atlantic, for a
distance of seventeen hundred miles from east to west, as well as we
know that of any part of the dry land.