autobiography and selected essays-第15部分

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respecting　the　conditions　of　animal　life；　and　it　is　not　so

absolutely　impossible　as　it　might　at　first　appear　to　be；　that　the

Globigerinae　of　the　Atlantic　sea…bottom　do　not　live　and　die　where

they　are　found。



As　I　have　mentioned；　the　soundings　from　the　great　Atlantic　plain

are　almost　entirely　made　up　of　Globigerinae；　with　the　granules

which　have　been　mentioned　and　some　few　other　calcareous　shells；　but

a　small　percentage　of　the　chalky　mudperhaps　at　most　some　five　per

cent　of　itis　of　a　different　nature；　and　consists　of　shells　and

skeletons　composed　of　silex；　or　pure　flint。　　These　silicious　bodies

belong　partly　to　the　lowly　vegetable　organisms　which　are　called

Diatomaceae；　and　partly　to　the　minute；　and　extremely　simple；

animals；　termed　Radiolaria。　　It　is　quite　certain　that　these

creatures　do　not　live　at　the　bottom　of　the　ocean；　but　at　its

surfacewhere　they　may　be　obtained　in　prodigious　numbers　by　the

use　of　a　properly　constructed　net。　　Hence　it　follows　that　these

silicious　organisms；　though　they　are　not　heavier　than　the　lightest

dust；　must　have　fallen；　in　some　cases；　through　fifteen　thousand

feet　of　water；　before　they　reached　their　final　resting…place　on　the

ocean　floor。　　And；　considering　how　large　a　surface　these　bodies

expose　in　proportion　to　their　weight；　it　is　probable　that　they

occupy　a　great　length　of　time　in　making　their　burial　journey　from

the　surface　of　the　Atlantic　to　the　bottom。



But　if　the　Radiolaria　and　Diatoms　are　thus　rained　upon　the　bottom

of　the　sea；　from　the　superficial　layer　of　its　waters　in　which　they

pass　their　lives；　it　is　obviously　possible　that　the　Globigerinae

may　be　similarly　derived；　and　if　they　were　so；　it　would　be　much

more　easy　to　understand　how　they　obtain　their　supply　of　food　than

it　is　at　present。　　Nevertheless；　the　positive　and　negative　evidence

all　points　the　other　way。　　The　skeletons　of　the　full…grown；　deep…

sea　Globigerinae　are　so　remarkably　solid　and　heavy　in　proportion　to

their　surface　as　to　seem　little　fitted　for　floating；　and；　as　a

matter　of　fact；　they　are　not　to　be　found　along　with　the　Diatoms　and

Radiolaria；　in　the　uppermost　stratum　of　the　open　ocean。



It　has　been　observed；　again；　that　the　abundance　of　Globigerinae；　in

proportion　to　other　organisms；　of　like　kind；　increases　with　the

depth　of　the　sea；　and　that　deep…water　Globigerinae　are　larger　than

those　which　live　in　shallower　parts　of　the　sea；　and　such　facts

negative　the　supposition　that　these　organisms　have　been　swept　by

currents　from　the　shallows　into　the　deeps　of　the　Atlantic。



It　therefore　seems　to　be　hardly　doubtful　that　these　wonderful

creatures　live　and　die　at　the　depths　in　which　they　are　found。



However；　the　important　points　for　us　are；　that　the　living

Globigerinae　are　exclusively　marine　animals；　the　skeletons　of　which

abound　at　the　bottom　of　deep　seas；　and　that　there　is　not　a　shadow

of　reason　for　believing　that　the　habits　of　the　Globigerinae　of　the

chalk　differed　from　those　of　the　existing　species。　　But　if　this　be

true；　there　is　no　escaping　the　conclusion　that　the　chalk　itself　is

the　dried　mud　of　an　ancient　deep　sea。



In　working　over　the　soundings　collected　by　Captain　Dayman；　I　was

surprised　to　find　that　many　of　what　I　have　called　the　〃granules〃　of

that　mud；　were　not；　as　one　might　have　been　tempted　to　think　at

first；　the　mere　powder　and　waste　of　Globigerinae；　but　that　they　had

a　definite　form　and　size。　　I　termed　these　bodies　〃coccoliths；〃　and

doubted　their　organic　nature。　　Dr。　Wallich　＇65＇　verified　my

observation；　and　added　the　interesting　discovery；　that；　not

unfrequently；　bodies　similar　to　these　〃coccoliths〃　were　aggregated

together　into　spheroids；　which　he　termed　〃coccospheres。〃　　So　far

as　we　knew；　these　bodies；　the　nature　of　which　is　extremely　puzzling

and　problematical；　were　peculiar　to　the　Atlantic　soundings。



But；　a　few　years　ago；　Mr。　Sorby；＇66＇　in　making　a　careful　examination

of　the　chalk　by　means　of　thin　sections　and　otherwise；　observed；　as

Ehrenberg　had　done　before　him；　that　much　of　its　granular　basis

possesses　a　definite　form。　　Comparing　these　formed　particles　with

those　in　the　Atlantic　soundings；　he　found　the　two　to　be　identical；

and　thus　proved　that　the　chalk；　like　the　soundings；　contains　these

mysterious　coccoliths　and　coccospheres。　　Here　was　a　further　and　a

most　interesting　confirmation；　from　internal　evidence；　of　the

essential　identity　of　the　chalk　with　modern　deep…sea　mud。

Globigerinae；　coccoliths；　and　coccospheres　are　round　as　the　chief

constituents　of　both；　and　testify　to　the　general　similarity　of　the

conditions　under　which　both　have　been　formed。



The　evidence　furnished　by　the　hewing；　facing；　and　superposition　of

the　stones　of　the　Pyramids；　that　these　structures　were　built　by

men；　has　no　greater　weight　than　the　evidence　that　the　chalk　was

built　by　Globigerinae；　and　the　belief　that　those　ancient　pyramid…

builders　were　terrestrial　and　air…breathing　creatures　like

ourselves；　is　it　not　better　based　than　the　conviction　that　the

chalk…makers　lived　in　the　sea？



But　as　our　belief　in　the　building　of　the　Pyramids　by　men　is　not

only　grounded　on　the　internal　evidences　afforded　by　these

structures；　but　gathers　strength　from　multitudinous　collateral

proofs；　and　is　clinched　by　the　total　absence　of　any　reason　for　a

contrary　belief；　so　the　evidence　drawn　from　the　Globigerinae　that

the　chalk　is　an　ancient　sea…bottom；　is　fortified　by　innumerable

independent　lines　of　evidence；　and　our　belief　in　the　truth　of　the

conclusion　to　which　all　positive　testimony　tends；　receives　the　like

negative　justification　from　the　fact　that　no　other　hypothesis　has　a

shadow　of　foundation。



It　may　be　worth　while　briefly　to　consider　a　few　of　these　collateral

proofs　that　the　chalk　was　deposited　at　the　bottom　of　the　sea。



The　great　mass　of　the　chalk　is　composed；　as　we　have　seen；　of　the

skeletons　of　Globigerinae；　and　other　simple　organisms；　imbedded　in

granular　matter。　　Here　and　there；　however；　this　hardened　mud　of　the

ancient　sea　reveals　the　remains　of　higher　animals　which　have　lived

and　died；　and　left　their　hard　parts　in　the　mud；　just　as　the　oysters

die　and　leave　their　shells　behind　them；　in　the　mud　of　the　present

seas。



There　are；　at　the　present　day；　certain　groups　of　animals　which　are

never　found　in　fresh　waters；　being　unable　to　live　anywhere　but　in

the　sea。　　Such　are　the　corals；　those　corallines　which　are　called

Polycoa；　those　creatures　which　fabricate　the　lamp…shells；　and　are

called　Brachiopoda；　the　pearly　Nautilus；　and　all　animals　allied　to

it；　and　all　the　forms　of　sea…urchins　and　star…fishes。



Not　only　are　all　these　creatures　confined　to　salt　water　at　the

present　day；　but；　so　far　as　our　records　of　the　past　go；　the

conditions　of　their　existence　have　been　the　same：　hence；　their

occurrence　in　any　deposit　is　as　strong　evidence　as　can　be　obtained；

that　that　deposit　was　formed　in　the　sea。　　Now　the　remains　of

animals　of　all　the　kinds　which　have　been　enumerated；　occur　in　the

chalk；　in　greater　or　less　abundance；　while　not　one　of　those　forms

of　shell…fish　which　are　characteristic　of　fresh　water　has　yet　been

observed　in　it。



When　we　consider　that　the　remains　of　more　than　three　thousand

distinct　species　of　aquatic　animals　have　been　discovered　among　the

fossils　of　the　chalk；　that　the　great　majority　of　them　are　of　such

forms　as　are　now　met　with　only　in　the　sea；　and　that　there　is　no

reason　to　believe　that　any　one　of　them　inhabited　fresh　waterthe

collateral　evidence　that　the　chalk　represents　an　ancient　sea…bottom

acquires　as　great　force　as　the　proof　derived　from　the　nature　of　the

chalk　itself。　　I　think　you　will　now　allow　that　I　did　not　overstate

my　case　when　I　asserted　that　we　have　as　strong　grounds　for

believing　that　all　the　vast　area　of　dry　land；　at　present　occupied

by　the　chalk；　was　once　at　the　bottom　of　the　sea；　as　we　have　for　any

matter　of　history　whatever；　while　there　is　no　justification　for　any

other　belief。



No　less　certain　it　is　that　the　time　during　which　the　countries　we

now　call　south…east　England；　France；　Germany；　Poland；　Russia；

Egypt；　Arabia；　Syria；　were　more　or　less　completely　covered　by　a

deep　sea；　was　of　considerable　duration。



We　have　already　seen　that　the　chalk　is；　in　places；　more　than　a

thousand　feet　thick。　　I　think　you　will　agree　with　me；　that　it　must

have　taken　some　time　for　the　skeletons　of　animalcules　of　a

hundredth　of　an　inch　in　diameter　to　heap　up　such　a　mass　as　that。　　I

have　said　that　throughout　the　thickness　of　the　chalk　the　remains　of

other　animals　are　scattered。　　These　remains　are　often　in　the　most

exquisite　state　of　preservation。　　The　valves　of　the　shell…fishes

are　commonly　adherent；　the　long　spines　of　some　of　the　sea…urchins；

which　would　be　detached　by　the　smallest　jar；　often　remain　in　their

places。　　In　a　word；　it　is　certain　that　these　animals　have　lived　and

died　when　the　place　which　they　now　occupy　was　the　surface　of　as

much　of　the　chalk　as　had　then　been　deposited；　and　that　each　has

been　covered　up　by　the　layer　of　Globigerina　mud；　upon　which　the

creatures　imbedded　a　little　higher　up　have；　in　like　manner；　lived

and　died。　　But　some　of　these　remains　prove　the　existence　of

reptiles　of　vast　size　in　the　chalk　sea。　　These　lived　their　time；

and　had　their　ancestors　and　descendants；　which　assuredly　implies

time；　reptiles　being　of　slow　growth。



There　is　more　curious　evidence；　again；　that　the　process　of　covering

up；　or；　in　other　words；　the　deposit　of　Globigerina　skeletons；　did

not　go　on　very　fast。　　It　is　demonstrable　that　an　animal　of　the

cretaceous　sea　might　die；　that　its　skeleton　might　lie　uncovered

upon　the　sea…bottom　long　enough　to　lose　all　its　outward　coverings

and　appendages　by　putrefaction；　and　that；　after　this　had　happened；

another　animal　might　attach　itself　to　the　dead　and　naked　skeleton；

might　grow　to　maturity；　and　might　itself　die　before　the　calcareous

mud　had　buried　the　whole。



Cases　of　this　kind　are　admirably　described　by　Sir　Char