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this coloured part indicates all the dry land； and this other portion
is the water。 You will notice at once that the water covers
three…fifths of the whole surface of the globe； and has covered it in
the same manner ever since man has kept any record of his own
observations； to say nothing of the minute period during which he has
cultivated geological inquiry。 So that three…fifths of the surface of
the earth is shut out from us because it is under the sea。 Let us look
at the other two…fifths； and see what are the countries in which
anything that may be termed searching geological inquiry has been
carried out： a good deal of France； Germany； and Great Britain and
Ireland； bits of Spain； of Italy； and of Russia； have been examined；
but of the whole great mass of Africa； except parts of the southern
extremity； we know next to nothing； little bits of India； but of the
greater part of the Asiatic continent nothing； bits of the Northern
American States and of Canada； but of the greater part of the continent
of North America； and in still larger proportion； of South America；
nothing！
Under these circumstances； it follows that even with reference to that
kind of imperfect information which we can possess； it is only of about
the ten…thousandth part of the accessible parts of the earth that has
been examined properly。 Therefore； it is with justice that the most
thoughtful of those who are concerned in these inquiries insist
continually upon the imperfection of the geological record； for； I
repeat； it is absolutely necessary； from the nature of things； that
that record should be of the most fragmentary and imperfect character。
Unfortunately this circumstance has been constantly forgotten。 Men of
science； like young colts in a fresh pasture； are apt to be exhilarated
on being turned into a new field of inquiry； to go off at a
hand…gallop； in total disregard of hedges and ditches； losing sight of
the real limitation of their inquiries； and to forget the extreme
imperfection of what is really known。 Geologists have imagined that
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