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they could tell us what was going on at all parts of the earth's
surface during a given epoch； they have talked of this deposit being
contemporaneous with that deposit； until； from our little local
histories of the changes at limited spots of the earth's surface； they
have constructed a universal history of the globe as full of wonders and
portents as any other story of antiquity。
But what does this attempt to construct a universal history of the globe
imply？ It implies that we shall not only have a precise knowledge of
the events which have occurred at any particular point； but that we
shall be able to say what events； at any one spot； took place at the
same time with those at other spots。
Let us see how far that is in the nature of things practicable。 Suppose
that here I make a section of the Lake of Killarney； and here the
section of another lakethat of Loch Lomond in Scotland for instance。
The rivers that flow into them are constantly carrying down deposits of
mud； and beds； or strata； are being as constantly formed； one above the
other； at the bottom of those lakes。 Now； there is not a shadow of
doubt that in these two lakes the lower beds are all older than the
upperthere is no doubt about that； but what does 'this' tell us about
the age of any given bed in Loch Lomond； as compared with that of any
given bed in the Lake of Killarney？ It is； indeed； obvious that if any
two sets of deposits are separated and discontinuous； there is
absolutely no means whatever given you by the nature of the deposit of
saying whether one is much younger or older than the other； but you may
say； as many have said and think； that the case is very much altered if
the beds which we are comparing are continuous。 Suppose two beds of
mud hardened into rock；A and B…are seen in section。 （Fig。 5。）
＇Fig。 5。＇
Well； you say； it is admitted that the lowermost bed is always the
older。 Very well； B； therefore； is older than A。 No doubt； 'as a
whole'； it is so； or if any parts of the two beds which are in the same
vertical line are compared； it is so。 But suppose you take what seems
a very natural step further； and say that the part 'a' of the bed A is
younger than the part 'b' of the bed B。 Is this sound reasoning？ If
you find any record of changes taking place at 'b'； did they occur
before any events which took place while 'a' was being deposited？ It
looks all very plain sailing； indeed； to say that they did； and yet
there is no proof of anything of the kind。 As the former Director of
this Institution； Sir H。 De la Beche； long ago showed； this reasoning
may involve an entire fallacy。 It is extremely possible that 'a' may
have been deposited ages before 'b'。 It is very easy to understand how
that can be。 To return to Fig。 4； when A and B were deposited； they
were 'substantially' contemporaneous； A being simply the finer deposit；
and B the coarser of the same detritus or waste of land。 Now suppose
that that sea…bottom goes down （as shown in Fig。 4）； so that the first
deposit is carried no farther than 'a'； forming the bed Al； and the
coarse no farther than 'b'； forming the bed B1； the result will be the
formation of two continuous beds； one of fine sediment （A A1）
over…lapping another of coarse sediment （B Bl）。 Now suppose the whole
sea…bottom is raised up； and a section exposed about the point Al； no
doubt； 'at this spot'； the upper bed is younger than the lower。 But we
should obviously greatly err if we concluded that the mass of the upper
bed at A was younger than the lower bed at B； for we have just seen
that they are contemporaneous deposits。 Still more should we be in
error if we supposed the upper bed at A to be younger than the
continuation of the lower bed at Bl； for A was deposited long before
B1。 In fine； if； instead of comparing immediately adjacent parts of
two beds； one of which lies upon another； we compare distant parts； it
is quite possible that the upper may be any number of years older than
the under； and the under any number of years younger than the upper。
Now you must not suppose that I put this before you for the purpose of
raising a paradoxical difficulty； the fact is； that the great mass of
deposits have taken place in sea…bottoms which are gradually sinking；
and have been formed under the very conditions I am here supposing。
Do not run away with the notion that this subverts the principle I laid
down at first。 The error lies in extending a principle which is
perfectly applicable to deposits in the same vertical line to deposits
which are not in that relation to one another。
It is in consequence of circumstances of this kind； and of others that I
might mention to you； that our conclusions on and interpretations of
the record are really and strictly only valid so long as we confine
ourselves to one vertical section。 I do not mean to tell you that there
are no qualifying circumstances； so that； even in very considerable
areas； we may safely speak of conformably superimposed beds being older
or younger than others at many different points。 But we can never be
quite sure in coming to that conclusion； and especially we cannot he
sure if there is any break in their continuity； or any very great
distance between the points to be compared。
Well now； so much for the record itself；so much for its
imperfections；so much for the conditions to be observed in
interpreting it； and its chronological indications； the moment we pass
beyond the limits of a vertical linear section。
Now let us pass from the record to that which it contains；from the
book itself to the writing and the figures on its pages。 This writing
and these figures consist of remains of animals and plants which； in
the great majority of cases； have lived and died in the very spot in
which we now find them； or at least in the immediate vicinity。 You
must all of you be awareand I referred to the fact in my last
lecturethat there are vast numbers of creatures living at the bottom
of the sea。 These creatures； like all others； sooner or later die； and
their shells and hard parts lie at the bottom； and then the fine mud
which is being constantly brought down by rivers and the action of the
wear and tear of the sea； covers them over and protects them from any
further change or alteration； and； of course； as in process of time the
mud becomes hardened and solidified； the shells of these animals are
preserved and firmly imbedded in the limestone or sandstone which is
being thus formed。 You may see in the galleries of the Museum up
stairs specimens of limestones in which such fossil remains of existing
animals are imbedded。 There are some specimens in which turtles' eggs
have been imbedded in calcareous sand； and before the sun had hatched
the young turtles； they became covered over with calcareous mud； and
thus have been preserved and fossilized。
Not only does this process of imbedding and fossilization occur with
marine and other aquatic animals and plants； but it affects those land
animals and plants which are drifted away to sea； or become buried in
bogs or morasses； and the animals which have been trodden down by their
fellows and crushed in the mud at the river's bank； as the herd have
come to drink。 In any of these cases； the organisms may be crushed or
be mutilated； before or after putrefaction； in such a manner that
perhaps only a part will be left in the form in which it reaches us。 It
is； indeed； a most remarkable fact； that it is quite an exceptional
case to find a skeleton of any one of all the thousands of wild land
animals that we know are constantly being killed； or dying in the
course of nature： they are preyed on and devoured by other animals or
die in places where their bodies are not afterwards protected by mud。
There are other animals existing in the sea； the shells of which form
exceedingly large deposits。 You are probably aware that before the
attempt was made to lay the Atlantic telegraphic cable； the Government
employed vessels in making a series of very careful observations and
soundings of the bottom of the Atlantic； and although； as we must all
regret； up to the present time that project has not succeeded； w