mode of occurrence _in situ_. The facts ascertained were communicated
to the Geological Society of London, the name "Eozoon Canadense"
being proposed for the species. Its description was accompanied by a
paper on the geological conditions by Logan, and one on the chemical
conditions by Sterry Hunt, while supplementary notes were added by
the late Dr. Carpenter and Professor T. Rupert Jones. Thus launched
on the scientific world, "Eozoon" at once became a fertile subject
of discussion, and volumes of more or less controversial literature
have appeared respecting it. It still has its friends and opponents,
and this may long continue, as so few scientific men are sufficiently
acquainted on the one hand with the possibilities and conditions of the
preservation of fossils in crystalline rocks, and on the other hand
with the structures of modern "Protozoa." Thus, few are in a position
to form an independent judgment, and "Eozoon" has met with some
scepticism on the part both of biological and mineralogical specialists.
To aid us in forming an opinion, it will be necessary to consider the
oldest known strata of the earth's crust, and the evidence which they
afford of the condition of the world when they were deposited. As
preliminary to this, we may look at the following table of pre-Cambrian
formations in Canada.
SUCCESSION OF PRE-CAMBRIAN ROCKS IN CANADA, AS UNDERSTOOD UP TO 1896.
(_In descending order._)
----------------------------------------------------
PALÆOZOIC.
{ Etcheminian in New Brunswick, _Kewenian_ or _Upper
{ Copper-bearing Series_ of Lake Superior, _Signal Hill
{ Series_ of Newfoundland. _Chuar_, and _Grand Cañon_
{ rocks of Colorado, etc.
{
{ Red and greenish Sandstones and Shales, Conglomerates,
{ Igneous Outflows and Ash-rocks. Bivalve
{ Crustacea, Mollusks, Worms, Sponges, Cystideans,
{ Zoophytes, Protozoa, Cryptozoon.
{ ----------------------------------------------------
(_Unconformity._)
----------------------------------------------------
EOZOIC.
{ Huronian, including _Hastings_ of Ontario, _Coldbrook_
{ and _Coastal_ of New Brunswick, _Algonkian_ (in part).
{ Conglomerates, Hard Sandstones, Shales and Schists,
{ Iron Ores, Coarse Limestones, Igneous Outflows, and
{ Ash-rocks. Worms, Sponges, Zoophytes, and Protozoa
{ (Cryptozoon or Eozoon).
----------------------------------------------------
(_Unconformity [?]_)
----------------------------------------------------
EOZOIC.
{ Grenvillian or Upper Laurentian.
{ Gneiss, Hornblendic and Micaceous Schists, Limestones,
{ Quartzite, Iron Ores, Graphite. Eozoon, Archæozoon,
{ Archæospherinæ, Archæophyton.
----------------------------------------------------
_Unconformity._
----------------------------------------------------
AZOIC
{ Archæan or Lower Laurentian.
{ Gneiss, Hornblende Schists, with many igneous or
{ igneo-aqueous intrusions.
_THE FOUNDATIONS OF THE CONTINENTS, AND
THEIR GENERAL TESTIMONY AS TO LIFE_
IV
_THE FOUNDATIONS OF THE CONTINENTS, AND
THEIR GENERAL TESTIMONY AS TO LIFE_
That the reader may be enabled better to understand the relation of
the old foundations or pillars of the earth to the beginning of life,
and the preservation of the remains of the earliest animals, it may be
well to reverse the method we have hitherto followed, and to present
a theoretical or ideal historical sketch of the early history of the
earth, beginning with that stage in which it may be supposed to have
been a liquid mass, considerably larger than it is at present, and
intensely heated, and surrounded by a vast vaporous envelope composed
of all the substances capable of being resolved by its heat into a
gaseous condition--a smooth and shining spheroid, invested with an
enormous atmosphere.
In such a condition its denser materials, such as the heavier metals,
would settle toward the centre, and the surface would consist of
lighter material composed of the less dense and more oxidizable
substances combined with oxygen, and similar in character and
appearance to the slag which forms on the surface of some ores in the
process of smelting. Of this slaggy material there might, however, be
different layers more or less dense in proceeding from the interior to
the surface. This molten surface would, of course, radiate heat into
space; and as it would naturally consist of the least fusible matters,
these would begin to form a solid crust. We may imagine this crust at
first to be smooth and unbroken, though such a condition could scarcely
exist for any length of time, as the hardened crust would certainly be
disturbed by ascending currents from within, and by tidal movements
without. Still, it might remain for ages as a spheroidal crust,
presenting little difference of elevation or depression in comparison
with its extent. When it became sufficiently thick and cool to allow
water to lie on its surface, new changes would begin. The water so
condensed would be charged with acid substances which would begin to
corrode the rocky surface. Penetrating into crevices and flashing into
steam as it reached the heated interior, it would blow up masses and
fragments of stone, and would perhaps force out and cause to flow over
the surface beds of molten material from below the crust, and differing
somewhat from it in their composition. All this aqueous work would
accelerate the cooling and thickening of the crust, and at length a
universal or almost universal heated ocean would envelope the globe,
and so far as its surface was concerned, the reign of water would
replace that of fire. We may pause here to consider the probable nature
of the earth's crust in this condition.
The substance most likely to predominate would be silica or quartz,
one of the lighter and most infusible materials of the crust; but
which, heated in contact with alumina, lime, potash, and other earths
and alkalis, forms fusible slags, enamels and glasses. One of these,
composed of silica, alumina, and potash, or soda, was long ago named
by the German miners felspar, a name which it still retains, though
now several distinct kinds of it are distinguished by different names.
Another is a compound of silica with magnesia and lime, forming the
mineral known as Amphibole or Hornblende, and by several other names,
according to its colour and crystalline form. In many deep-seated
rocks these minerals are formed together, and having crystallized
out separately give a spotted and granular character to the mass.
Naturally colourless, all these minerals, and especially the felspar
and hornblende, are liable to be coloured with different oxides of
iron, the felspar usually taking a reddish, and the hornblende a
greenish or blackish hue. Now, if we examine a fragment of the oldest
or fundamental gneiss or granite, we shall see glassy grains of quartz,
reddish or white flat-surfaced crystals of felspar, and dark-coloured
prisms of hornblende. When destitute of any arrangement in layers, the
rock is granite; when arranged more or less in flakes or laminæ, it is
gneiss, the structure of which may arise either from its having been
formed in successive beds, or from its having been flattened or drawn
out by pressure. These structures can be seen more or less distinctly
in any ordinary coarse-grained granite, or with the lens or microscope
in finer varieties.
The Lower Laurentian rocks of our section consist essentially of the
materials above described, with a vast variety in the proportions
and arrangements of the constituent minerals. There is, there-fore,
nothing to prevent us from supposing that these rocks are really
remains of the lower portions of the original crust which first formed
on the surface of our cooling planet, though the details of their
consolidation and the possible interactions of heat and heated water
may admit of much discussion and difference of opinion.
But after the formation of a crust and its covering in whole or in
part with heated water, other changes must occur, in order to fit the
earth for the abode of life. These proceeded from the tensions set
up by the contraction and expansion of the interior heated nucleus
and the solid crust--a complicated and difficult question, when we
consider its laws and their mode of operation, but which resulted in
the folding and fracturing of the crust along long lines which are
parts of great circles of the earth, running in N.E. and S.W. and N.W.
and S.E. directions; and these ridges, which in the earliest Archæan
period must have attained to great height and very rugged outlines,
formed the first rudiments of our mountain chains and continents. Those
constituting the Laurentian nucleus of North America--a very simply
outlined continent--form a case in point (Fig. 18).
The elevation of these mountain ridges forced the waters to recede into
the lower levels. As the old psalm of creation has it,--
"The mountains ascend,
the valleys descend into
the place Thou hast founded
for them,"
and so sea-basins and land were produced.
Milton merely paraphrases this when he says,--
"The mountains huge appear
Emergent, and their broad, bare backs upheave
Into the clouds; their tops ascend the sky.
So high as heaved the tumid hills, so low
Down sunk a hollow bottom wide and deep.
Capacious bed of waters."
Englishmen have been accused of taking their ideas of creation from
Milton rather than from nature or the Bible. Milton had not the
guidance of modern geology. His cosmology is entirely that of a close
student of the Biblical narrative of creation. He is in many respects
the best commentator on the early chapters of Genesis, because he
had a very clear conception of the mind of the writer, and the power
of expressing the ideas he derived from the old record. For the same
reason he is the greatest bard of creation and primitive man, and
surprisingly accurate and true to nature.
[Illustration: Fig. 18.--_Map of Laurentian, North America._
Showing the protaxis or nucleus of the continent.]
Then began the great processes of denudation and sedimentation to which
we owe the succeeding rock formations. The rains descended on the
mountain steeps, and washed the decaying rocks as sand, gravel and mud
into the rivers and the sea. The sea itself raged against the coasts,
and cut deeply into their softer parts; and all the detritus thus
produced by atmospheric and marine denudation was spread out by the
tides and currents in the bed of the ocean, and its gulfs and seas,
forming the first aqueous deposits, while the original land must have
been correspondingly reduced.
The sea might still be warm, and it held in solution or suspension
somewhat different substances from those now present in it, and the
land was at first a mere chaos of rocky crags and pinnacles. But so
soon as the temperature of the waters fell somewhat below the boiling
point, and as even a little soil formed in the valleys and hollows of
the land, there was scope for life, provided that its germs could be
introduced.
On a small scale there was something of this same kind in the sea
and land of Java, after the great eruption of Krakatoa, in 1883. The
bare and arid mountain left after the eruption, began, in the course
of a year, to be occupied by low forms of vegetable life, gradually
followed by others, and verdure was soon restored. The once thickly
peopled sea-bottom, so prolific of life in these warm seas, but
buried under many feet of volcanic ashes and stones, soon began to be
re-peopled, and is now probably as populous as before. But in this
case there were plenty of spores of lichens, mosses, and other humble
plants to be wafted to the desolate cone, and multitudes of eggs and
free-swimming germs of hundreds of kinds of marine animals to re-people
the sea-bottom. Whence were such things to come from to occupy the
old Archæan hills and sea-basins? and all our knowledge of nature
gives us no answer to the question, except that a creative power must
have intervened; but in what manner we know not. That this actually
occurred, we can, however, be assured by the next succeeding geological
formation. We have seen that the granitic and gneissic ridges could
furnish pebbles, sand, and clay, and these once deposited in the
sea-bottom could be hardened into conglomerate, sandstone and slate.
But beside these we have in the next succeeding or Upper Laurentian
formation rocks of a very different character. We have great beds of
limestone and iron ore, and deposits, of carbon or coaly matter, now
in the peculiar state of graphite or plumbago, and it is necessary
for us to inquire how these could originate independently of life. In
modern seas limestone is forming in coral reefs, in shell beds, and in
oceanic chalky ooze composed of minute microscopic shells; but only in
rare and exceptional instances is it formed in any other way; and when
we interrogate the old limestones and marbles which form parts of the
land, they give us evidence that they also are made up of calcareous
skeletons of marine animals or fragments of these.
[Illustration: Fig. 19.--_Distribution of Grenville Limestone in
the district north of Papineauville, with section showing supposed
arrangement of the beds._]
Scale of Map 7 miles to one inch. See also Dr. Bonney's paper, _Geol.
Mag._, July, 1895.
_Dotted area:_ Limestone. _Horizontal lines:_ Upper gneiss (fourth
gneiss of Logan). _Vertical lines:_ Lower gneiss (third gneiss of
Logan). _Diagonal lines:_ Overlying Cambrian and Cambro-Silurian
(Ordovician). (See also Fig. 19A.)
Now when we find in the Grenvillian series, the first oceanic group of
beds known to us, great and widely extended limestones, thousands of
feet in thickness, and rivalling in magnitude those of any succeeding
period, we naturally infer that marine life was at work. No doubt
the primitive sea contained more lime and magnesia than the present
ocean holds in solution; but while this might locally favour the
accumulation of inorganic limestones, it cannot account for so great
and extensive deposits. On the other hand, a sea rich in lime would
have afforded the greatest facilities for the growth of those marine
plants which accumulate lime, and through these for the nutrition of
animals forming calcareous shells or corals. Thus we have presumptive
evidence that there must have been in the Upper Laurentian sea
something corresponding to our coral reefs and shell-beds, whatever
this something may have been.
These limestones, however, demand more particular notice (Fig. 19).
One of the beds measured by the officers of the Geological Survey is
stated to be 1,500 feet in thickness, another is 1,250 feet thick,
and a third 750 feet; making an aggregate of 3,500 feet.[14] These
beds may be traced, with more or less interruption, for hundreds of
miles. Whatever the origin of such limestones, it is plain that they
indicate causes equal in extent, and comparable in power and duration,
with those which have produced the greatest limestones of the later
geological periods. Now, in later formations, limestone is usually an
organic rock, accumulated by the slow gathering from the sea-water,
or its plants, of calcareous matter, by corals, foraminifera, or
shell-fish, and the deposition of their skeletons, either entire or
in fragments on the sea-bottom. The most friable chalk and the most
crystalline limestones have alike been formed in this way. We know of
no reason why it should be different in the Laurentian period. When,
therefore, we find great and conformable beds of limestone, such as
those described by Sir William Logan in the Laurentian of Canada, we
naturally imagine a quiet sea-bottom, in which multitudes of animals of
humble organization were accumulating limestone in their hard parts,
and depositing this in gradually increasing thickness from age to age.
Any attempts to account otherwise for these thick and greatly extended
beds, regularly interstratified with other deposits, have so far been
failures, and have arisen either from a want of comprehension of the
nature and magnitude of the appearances to be explained, or from the
error of mistaking the true bedded limestones for veins of calcareous
spar.
[Footnote 14: Logan: "Geology of Canada," p. 45.]
[Illustration: Fig. 19A.--_Attitude of Limestone at Côte St. Pierre_
(see Map, p. 88).
(_a_) Gneiss band in the Limestone, (_b_) Limestone with Eozoon. (_c_)
Diorite and Gneiss.]
Again, in the original molten world, it seems likely that most of
the carbon present--at least, at the surface--was in the atmosphere
in the gaseous form of carbon dioxide. This might be dissolved by
the rain and other waters; but we know in the modern world no agency
which can decompose this compound and reduce it to ordinary carbon
or coal, except that of living plants, which are always carrying on
this function to an enormous extent. We know that all our great beds
of coal and peaty matter are composed of the remains of plants which
took their carbon from the air and the waters in past times. We also
know that this coaly vegetable matter may, under the influence of heat
and pressure, when buried in the earth, be converted into anthracite
and into graphite, and even into diamond. It is true that an eminent
French chemist[15] has shown that graphite and hydrocarbons may be
produced from some of the metallic compounds of carbon which may have
been formed under intense heat in the interior of the earth, by the
subsequent action of water on such compounds; but there is nothing to
show that this can have occurred naturally, unless in very exceptional
cases. Now in the Grenvillian system in Canada there is not only a
vast quantity of carbon diffused through the limestones, and filling
fissures in other rocks, into which it seems to have been originally
introduced as liquid bitumen, but also in definite beds associated with
earthy matter, and sometimes ten to twelve feet thick. The occurrence
of this large amount of carbon warrants us in supposing that it
represents a vast vegetable growth, either on the land or in the sea,
or both.
[Footnote 15: Henri Moissan, "Proceedings Royal Society," June, 1896,]
In like manner, in later geological periods, beds of iron ore are
generally accumulated as a consequence of the solvent action of
acids produced by vegetable decay, as in the clay ironstones of the
coal formation and the bog iron ores of later times. Thus the beds
of magnetic iron occurring in the Upper Laurentian may be taken as
evidences, not of vegetable accumulation, but of vegetable decay.
May not also the great quantity of calcium phosphate mined in the
Grenville series in Canada, indicate, as similar accumulations do in
later formations, the presence of organisms having skeletons of bone
earth?
With reference to the carbon and iron ore of the Grenville series, I
may quote the following from a paper published in the _Journal of the
Geological Society of London_ in 1870:--
"The quantity of graphite in the Upper Laurentian series is enormous.
In a recent visit to the township of Buckingham, on the Ottawa River,
I examined a band of limestone believed to be a continuation of that
described by Sir W. E. Logan as the Green Lake Limestone. It was
estimated to amount, with some thin interstratified bands of gneiss,
to a thickness of 600 feet or more, and was found to be filled with
disseminated crystals of graphite and veins of the mineral to such
an extent as to constitute in some places one-fourth of the whole;
and making every allowance for the poorer portions, this band cannot
contain in all a less vertical thickness of pure graphite than from
twenty to thirty feet. In the adjoining township of Lochaber Sir W. E.
Logan notices a band from twenty-five to thirty feet thick, reticulated
with graphite veins to such an extent as to be mined with profit for
the mineral. At another place in the same district a bed of graphite
from ten to twelve feet thick, and yielding twenty per cent, of the
pure material, is worked. When it is considered that graphite occurs in
similar abundance at several other horizons, in beds of limestone which
have been ascertained by Sir W. E. Logan to have an aggregate thickness
of 3,500 feet, it is scarcely an exaggeration to maintain that the
quantity of carbon in the Laurentian is equal to that in similar areas
of the Carboniferous system. It is also to be observed that an immense
area in Canada appears to be occupied by these graphitic and Eozoon
limestones, and that rich graphitic deposits exist in the continuation
of this system in the State of New York; while in rocks believed to be
of this age near St. John, New Brunswick, there is a very thick bed
of graphitic limestone, and associated with it three regular beds of
graphite, having an aggregate thickness of about five feet.[16]
[Footnote 16: Matthew, in _Quart. Journ. Geol. Soc._, vol. xxi. p. 423.
"Acadian Geology," p. 662.]
"It may fairly be assumed that in the present world, and in those
geological periods with whose organic remains we are more familiar than
with those of the Laurentian, there is no other source of unoxidized
carbon in rocks than that furnished by organic matter, and that this
has obtained its carbon in all cases, in the first instance, from the
deoxidation of carbonic acid by living plants. No other source of
carbon can, I believe, be imagined in the Laurentian period. We may,
however, suppose either that the graphitic matter of the Laurentian
has been accumulated in beds like those of coal, or that it has
consisted of diffused bituminous matter similar to that in more
modern bituminous shales and bituminous and oil-bearing limestones.
The beds of graphite near St. John, some of those in the gneiss at
Ticonderoga in New York, and at Lochaber and Buckingham and elsewhere
in Canada, are so pure and regular that one might fairly compare them
with the graphitic coal of Rhode Island. These instances, however, are
exceptional, and the greater part of the disseminated and vein graphite
might rather be compared in its mode of occurrence to the bituminous
matter in bituminous shales and limestones.
"We may compare the disseminated graphite to that which we find in
those districts of Canada in which Silurian and Devonian bituminous
shales and limestones have been metamorphosed and converted into
graphitic rocks not dissimilar to those in the less altered portions of
the Laurentian.[17] In like manner it seems probable that the numerous
reticulating veins of graphite may have been formed by the segregation
of bituminous matter into fissures and planes of least resistance, in
the manner in which such veins occur in modern bituminous limestones
and shales. Such bituminous veins occur in the Lower Carboniferous
limestone and shale of Dorchester and Hillsborough, New Brunswick, with
an arrangement very similar to that of the veins of graphite; and in
the Quebec rocks of Point Levi, veins attaining to a thickness of more
than a foot are filled with a coaly matter having a transverse columnar
structure, and regarded by Logan and Hunt as an altered bitumen.
These Palæozoic analogies would lead us to infer that the larger part
of the Laurentian graphite falls under the second class of deposits
above mentioned, and that, if of vegetable origin, the organic matter
must have been thoroughly disintegrated and bituminized before it was
changed into graphite. This would also give a probability that the
vegetation implied was aquatic, or at least that it was accumulated
under water.
[Footnote 17: Granby, Melbourne, Owl's Head, etc., "Geology of Canada,"
1863, p. 599.]
"Dr. Hunt has, however, observed an indication of terrestrial
vegetation, or at least of subaërial decay, in the great beds of
Laurentian iron ore. These, if formed in the same manner as more modern
deposits of this kind, would imply the reducing and solvent action of
substances produced in the decay of plants. In this case such great
ore beds as that of Hull, on the Ottawa, 70 feet thick, or that near
Newborough, 200 feet thick,[18] must represent a corresponding quantity
of vegetable matter which has totally disappeared. It may be added that
similar demands on vegetable matter as a deoxidizing agent are made
by the beds and veins of metallic sulphides of the Laurentian, though
some of the latter are no doubt of later date than the Laurentian rocks
themselves.
[Footnote 18: "Geology of Canada," 1863.]