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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； we have
the satisfaction of knowing that it yielded some most remarkable results
to science。 The Atlantic Ocean had to be sounded right across； to
depths of several miles in some places； and the nature of its bottom
was carefully ascertained。 Well； now； a space of about 1；000 miles
wide from east to west； and I do not exactly know how many from north to
south； but at any rate 600 or 700 miles； was carefully examined； and it
was found that over the whole of that immense area an excessively fine
chalky mud is being deposited； and this deposit is entirely made up of
animals whose hard parts are deposited in this part of the ocean； and
are doubtless gradually acquiring solidity and becoming metamorphosed
into a chalky limestone。 Thus； you see； it is quite possible in this
way to preserve unmistakable records of animal and vegetable life。
Whenever the sea…bottom； by some of those undulations of the earth's
crust that I have referred to； becomes upheaved； and sections or
borings are made； or pits are dug； then we become able to examine the
contents and constituents of these ancient sea…bottoms； and find out
what manner of animals lived at that period。
Now it is a very important consideration in its bearing on the
completeness of the record； to inquire how far the remains contained in
these fossiliferous limestones are able to convey anything like an
accurate or complete account of the animals which were in existence at
the time of its formation。 Upon that point we can form a very clear
judgment； and one in which there is no possible room for any mistake。
There are of course a great number of animalssuch as jelly…fishes；
and other animalswithout any hard parts； of which we cannot
reasonably expect to find any traces whatever： there is nothing of them
to preserve。 Within a very short time； you will have noticed； after
they are removed from the water； they dry up to a mere nothing；
certainly they are not of a nature to leave any very visible traces of
their existence on such bodies as chalk or mud。 Then again； look at
land animals； it is； as I have said； a very uncommon thing to find a
land animal entire after death。 Insects and other carnivorous animals
very speedily pull them to pieces； putrefaction takes place； and so； out
of the hundreds of thousands that are known to die every year； it is
the rarest thing in the world to see one imbedded in such a way that
its remains would be preserved for a lengthened period。 Not only is
this the case； but even when animal remains have been safely imbedded；
certain natural agents may wholly destroy and remove them。
Almost all the hard parts of animalsthe bones and so onare composed
chiefly of phosphate of lime and carbonate of lime。 Some years ago； I
had to make an inquiry into the nature of some very curious fossils
sent to me from the North of Scotland。 Fossils are usually hard bony
structures that have become imbedded in the way I have described； and
have gradually acquired the nature and solidity of the body with which
they are associated； but in this case I had a series of 'holes' in some
pieces of rock； and nothing else。 Those holes； however； had a certain
definite shape about them； and when I got a skilful workman to make
castings of the interior of these holes； I found that they were the
impressions of the joints of a backbone and of the armour of a great
reptile； twelve or more feet long。 This great beast had died and got
buried in the sand； the sand had gradually hardened over the bones； but
remained porous。 Water had trickled through it； and that water being
probably charged with a superfluity of carbonic acid； had dissolved all
the phosphate and carbonate of lime； and the bones themselves had thus
decayed and entirely disappeared； but as the sandstone happened to have
consolidated by that time； the precise shape of the bones was retained。
If that sandstone had remained soft a little longer； we should have
known nothing whatsoever of the existence of the reptile whose bones