autobiography and selected essays-第14部分

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bodies　are　of　various　forms。　　One　of　the　commonest　is　something

like　a　badly　grown　raspberry；　being　formed　of　a　number　of　nearly

globular　chambers　of　different　sizes　congregated　together。　　It　is

called　Globigerina；　and　some　specimens　of　chalk　consist　of　little

else　than　Globigerina　and　granules。



Let　us　fix　our　attention　upon　the　Globigerina。　　It　is　the　spoor　of

the　game　we　are　tracking。　　If　we　can　learn　what　it　is　and　what　are

the　conditions　of　its　existence；　we　shall　see　our　way　to　the　origin

and　past　history　of　the　chalk。



A　suggestion　which　may　naturally　enough　present　itself　is；　that

these　curious　bodies　are　the　result　of　some　process　of　aggregation

which　has　taken　place　in　the　carbonate　of　lime；　that；　just　as　in

winter；　the　rime　on　our　windows　simulates　the　most　delicate　and

elegantly　arborescent　foliageproving　that　the　mere　mineral　water

may；　under　certain　conditions；　assume　the　outward　form　of　organic

bodiesso　this　mineral　substance；　carbonate　of　lime；　hidden　away

in　the　bowels　of　the　earth；　has　taken　the　shape　of　these　chambered

bodies。　　I　am　not　raising　a　merely　fanciful　and　unreal　objection。

Very　learned　men；　in　former　days；　have　even　entertained　the　notion

that　all　the　formed　things　found　in　rocks　are　of　this　nature；　and

if　no　such　conception　is　at　present　held　to　be　admissible；　it　is

because　long　and　varied　experience　has　now　shown　that　mineral

matter　never　does　assume　the　form　and　structure　we　find　in　fossils。

If　any　one　were　to　try　to　persuade　you　that　an　oyster…shell　（which

is　also　chiefly　composed　of　carbonate　of　lime）　had　crystallized　out

of　sea…water；　I　suppose　you　would　laugh　at　the　absurdity。　　Your

laughter　would　be　justified　by　the　fact　that　all　experience　tends

to　show　that　oyster…shells　are　formed　by　the　agency　of　oysters；　and

in　no　other　way。　　And　if　there　were　no　better　reasons；　we　should　be

justified；　on　like　grounds；　in　believing　that　Globigerina　is　not

the　product　of　anything　but　vital　activity。



Happily；　however；　better　evidence　in　proof　of　the　organic　nature　of

the　Globigerinae　than　that　of　analogy　is　forthcoming。　　It　so

happens　that　calcareous　skeletons；　exactly　similar　to　the

Globigerinae　of　the　chalk；　are　being　formed；　at　the　present　moment；

by　minute　living　creatures；　which　flourish　in　multitudes；　literally

more　numerous　than　the　sands　of　the　sea…shore；　over　a　large　extent

of　that　part　of　the　earth's　surface　which　is　covered　by　the　ocean。



The　history　of　the　discovery　of　these　living　Globigerinae；　and　of

the　part　which　they　play　in　rock　building；　is　singular　enough。　　It

is　a　discovery　which；　like　others　of　no　less　scientific　importance；

has　arisen；　incidentally；　out　of　work　devoted　to　very　different　and

exceedingly　practical　interests。



When　men　first　took　to　the　sea；　they　speedily　learned　to　look　out

for　shoals　and　rocks；　and　the　more　the　burthen　of　their　ships

increased；　the　more　imperatively　necessary　it　became　for　sailors　to

ascertain　with　precision　the　depths　of　the　waters　they　traversed。

Out　of　this　necessity　grew　the　use　of　the　lead　and　sounding　line；

and；　ultimately；　marine…surveying；　which　is　the　recording　of　the

form　of　coasts　and　of　the　depth　of　the　sea；　as　ascertained　by　the

sounding…lead；　upon　charts。



At　the　same　time；　it　became　desirable　to　ascertain　and　to　indicate

the　nature　of　the　sea…bottom；　since　this　circumstance　greatly

affects　its　goodness　as　holding　ground　for　anchors。　　Some　ingenious

tar；　whose　name　deserves　a　better　fate　than　the　oblivion　into　which

it　has　fallen；　attained　this　object　by　〃arming〃　the　bottom　of　the

lead　with　a　lump　of　grease；　to　which　more　or　less　of　the　sand　or

mud；　or　broken　shells；　as　the　case　might　be；　adhered；　and　was

brought　to　the　surface。　　But；　however　well　adapted　such　an

apparatus　might　be　for　rough　nautical　purposes；　scientific　accuracy

could　not　be　expected　from　the　armed　lead；　and　to　remedy　its

defects　（especially　when　applied　to　sounding　in　great　depths）

Lieut。　Brooke；＇61＇　of　the　American　Navy；　some　years　ago　invented

a　most　ingenious　machine；　by　which　a　considerable　portion　of　the

superficial　layer　of　the　sea…bottom　can　be　scooped　out　and　brought

up　from　any　depth　to　which　the　lead　descends。



In　1853；　Lieut。　Brooke　obtained　mud　from　the　bottom　of　the　North

Atlantic；　between　Newfoundland　and　the　Azores；　at　a　depth　of　more

than　ten　thousand　feet；　or　two　miles；　by　the　help　of　this　sounding

apparatus。　　The　specimens　were　sent　for　examination　to　Ehrenberg　＇62＇

of　Berlin；　and　to　Bailey　of　West　Point；＇63＇　and　those　able

microscopists　found　that　this　deep…sea　mud　was　almost　entirely

composed　of　the　skeletons　of　living　organismsthe　greater　proportion

of　these　being　just　like　the　Globigerinae　already　known　to　occur

in　the　chalk。



Thus　far；　the　work　had　been　carried　on　simply　in　the　interests　of

science；　but　Lieut。　Brooke's　method　of　sounding　acquired　a　high

commercial　value；　when　the　enterprise　of　laying　down　the　telegraph…

cable　＇64＇　between　this　country　and　the　United　States　was　undertaken。

For　it　became　a　matter　of　immense　importance　to　know；　not　only　the

depth　of　the　sea　over　the　whole　line　along　which　the　cable　was　to

be　laid；　but　the　exact　nature　of　the　bottom；　so　as　to　guard　against

chances　of　cutting　or　fraying　the　strands　of　that　costly　rope。　　The

Admiralty　consequently　ordered　Captain　Dayman；　an　old　friend　and

shipmate　of　mine；　to　ascertain　the　depth　over　the　whole　line　of　the

cable；　and　to　bring　back　specimens　of　the　bottom。　　In　former　days；

such　a　command　as　this　might　have　sounded　very　much　like　one　of　the

impossible　things　which　the　young　prince　in　the　Fairy　Tales　is

ordered　to　do　before　he　can　obtain　the　hand　of　the　Princess。

However；　in　the　months　of　June　and　July；　1857；　my　friend　performed

the　task　assigned　to　him　with　great　expedition　and　precision

without；　so　far　as　I　know；　having　met　with　any　reward　of　that　kind。

The　specimens　of　Atlantic　mud　which　he　procured　were　sent　to　me　to

be　examined　and　reported　upon。*





*　See　Appendix　to　Captain　Dayman's　〃Deep…sea　Soundings　in　the　North

Atlantic　Ocean；　between　Ireland　and　Newfoundland；　made　in　H。M。S。

Cyclops。　　Published　by　order　of　the　Lords　Commissioners　of　the

Admiralty；　1858。〃　　They　have　since　formed　the　subject　of　an

elaborate　Memoir　by　Messrs。　Parker　and　Jones；　published　in　the

Philosophical　Transactions　for　1865。





The　result　of　all　these　operations　is；　that　we　know　the　contours

and　the　nature　of　the　surface…soil　covered　by　the　North　Atlantic；

for　a　distance　of　seventeen　hundred　miles　from　east　to　west；　as

well　as　we　know　that　of　any　part　of　the　dry　land。



It　is　a　prodigious　plainone　of　the　widest　and　most　even　plains　in

the　world。　　If　the　sea　were　drained　off；　you　might　drive　a　wagon

all　the　way　from　Valentia；　on　the　west　coast　of　Ireland；　to　Trinity

Bay；　in　Newfoundland。　　And；　except　upon　one　sharp　incline　about　two

hundred　miles　from　Valentia；　I　am　not　quite　sure　that　it　would　even

be　necessary　to　put　the　skid　on；　so　gentle　are　the　ascents　and

descents　upon　that　long　route。　　From　Valentia　the　road　would　lie

down…hill　for　about　200　miles　to　the　point　at　which　the　bottom　is

now　covered　by　1700　fathoms　of　sea…water。　　Then　would　come　the

central　plain；　more　than　a　thousand　miles　wide；　the　inequalities　of

the　surface　of　which　would　be　hardly　perceptible；　though　the　depth

of　water　upon　it　now　varies　from　10；000　to　15；000　feet；　and　there

are　places　in　which　Mont　Blanc　might　be　sunk　without　showing　its

peak　above　water。　　Beyond　this；　the　ascent　on　the　American　side

commences；　and　gradually　leads；　for　about　300　miles；　to　the

Newfoundland　shore。



Almost　the　whole　of　the　bottom　of　this　central　plain　（which　extends

for　many　hundred　miles　in　a　north　and　south　direction）　is　covered

by　a　fine　mud；　which；　when　brought　to　the　surface；　dries　into　a

greyish…white　friable　substance。　　You　can　write　with　this　on　a

blackboard；　if　you　are　so　inclined；　and；　to　the　eye；　it　is　quite

like　very　soft；　greyish　chalk。　　Examined　chemically；　it　proves　to

be　composed　almost　wholly　of　carbonate　of　lime；　and　if　you　make　a

section　of　it；　in　the　same　way　as　that　of　the　piece　of　chalk　was

made；　and　view　it　with　the　microscope；　it　presents　innumerable

Globigerinae　embedded　in　a　granular　matrix。



Thus　this　deep…sea　mud　is　substantially　chalk。　　I　say

substantially；　because　there　are　a　good　many　minor　differences；　but

as　these　have　no　bearing　on　the　question　immediately　before　us；

which　is　the　nature　of　the　Globigerinae　of　the　chalk；it　is

unnecessary　to　speak　of　them。



Globigerinae　of　every　size；　from　the　smallest　to　the　largest；　are

associated　together　in　the　Atlantic　mud；　and　the　chambers　of　many

are　filled　by　a　soft　animal　matter。　　This　soft　substance　is；　in

fact；　the　remains　of　the　creature　to　which　the　Globigerina　shell；

or　rather　skeleton；　owes　its　existenceand　which　is　an　animal　of

the　simplest　imaginable　description。　　It　is；　in　fact；　a　mere

particle　of　living　jelly；　without　defined　parts　of　any　kind

without　a　mouth；　nerves；　muscles；　or　distinct　organs；　and　only

manifesting　its　vitality　to　ordinary　observation　by　thrusting　out

and　retracting　from　all　parts　of　its　surface；　long　filamentous

processes；　which　serve　for　arms　and　legs。　　Yet　this　amorphous

particle；　devoid　of　everything　which；　in　the　higher　animals；　we

call　organs；　is　capable　of　feeding；　growing　and　multiplying；　of

separating　from　the　ocean　the　small　proportion　of　carbonate　of　lime

which　is　dissolved　in　sea…water；　and　of　building　up　that　substance

into　a　skeleton　for　itself；　according　to　a　pattern　which　can　be

imitated　by　no　other　known　agency。



The　notion　that　animals　can　live　and　flourish　in　the　sea；　at　the

vast　depths　from　which　apparently　living　Globigerinae　have　been

brought　up；　does　not　agree　very　well　with　our　usual　conceptions

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

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