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55
forskjellige Forhold, der endnu er os fuldkommen ubekjendte.
Vi har saaledes ingen Erfaring 0111 de kvantitative og
temporære Betingelser, der er givne for Globigerinernes
Attei-ring paa Havbunden. Lige saa lidt kan vi af de i
Bund-prøverne fundne Skaller af ikke-pelagiske Foraminiferer
slutte os til, hvor stærkt de levende Dyr har været
repræsenterede i Slammet, eller hvorlænge de døde Dyrs Skaller
vil opbevares paa Havbunden — tvende Spørgsmaal, der
vel maa have sin Betydning for Slammets mekaniske
Af-leiring. Det er dog rimeligt at antage, at lang Tid kræves,
for at Søvandet skal kunne opløse disse Kalkskaller. Vi
ved af tidligere Forsøg, at de paa Grund af sin Gehalt paa
organiske Stoffe ikke forholder sig som ren kulsur Kalk
ligeoverfor Opløsningsmidler, men at de angribes langt
vanskeligere. Man bar fremsat den Paastand, at den kulsure
Kalk lettere opløses i Dybet paa Grund af den større
Mængde Kulsyre, som her skulde lindes i Søvandet. Hr.
Tornøes Undersøgelser over Kulsyremængden i det af den
norske Expedition beseilede Hav modbeviser imidlertid denne
Antagelse. Han har fundet, at Søvandet overalt reagerer
alkalisk og altsaa ikke kan indeholde nogen fri, meu blot
normalt- og surtbunden Kulsyre; Mængden af denne er
imidlertid paa Dybet omtrent den samme som ved
Overfladen. At Forholdet skulde være anderledes i de øvrige
Dele af Oceanet synes ikke at have nogen Sandsynlighed
for sig, naar man ser hen til de talrige Undersøgelser, der
stadfæster Søvandets Ensartethed med Hensyn til dets
øvrige Bestanddele. Søvandets opløsende Evne ligeoverfor
den kulsure Kalk skyldes altsaa ikke dets Gehalt paa fri
Kulsyre.
Den ovenomtalte Lagdannelse i Biloculinleret. kan
ogsaa tænkes fremkommet ved en Slemningsproces, hvis
Vandets Strømninger paa Bunden er stærke nok til at
sætte Slammets line Partikler i Bevægelse. Dette
Spørgsmaal er imidlertid lige saa ubesvaret som de foregaaende.
Det fortjener imidlertid at nævnes, at alle de fra Bunden
optagne Vandprøver altid var ganske klare og uden Spor
af svævende Partikler.
Betragter vi paa Kartet den østlige Grænclselinie for
Biloculinleret, vil vi linde, at den i Almindelighed gaar
imellem 900 og 1100 Favne. Imidlertid træffer vi dog paa
flere Steder Biloculinleret paa mindre Dyb, ligesom det
ogsaa hænder, at det først begynder at vise sig under 1100
Favne. Mellem 04° og 08° N. B. gaar Biloculinlerets
vestlige Grændse op til et grundere Dyb end længere Nord.
Paa Stationerne 54, 96 og 248 møder vi det saaledes
allerede paa 600, 805 og 778 Favne. Udenom den sidstnævnte
Station, der ligger omtrent 50 Mile fra Laiid, gjør
Dybdekurverne for 800;—1000 Favne en skarp Bøining (sml. Side
40) indover mod Kysten indtil en Afstand fra denne af ca.
30 Mile; paa denne Strækning ligger Grændsen for
Biloculinleret imellem 700 og 800 Favne. Paa den bråt
skraanende Havbund udenfor Lofoten og Vesteraalen finder vi
an intimate acquaintance with divers conditions as yet
wholly unknown. Thus, for instance, we have everything
to learn respecting the causes that determine the
quantitative and temporary distribution of Globigerinæ over the
sea-bed. Nor can we from the proportion of non-pelagic
foraminiferous shells infer how numerously the living
animals were represented in the deposit or the length of the
period during which their shells are preserved from
decomposition at the bottom of the sea — questions which cannot
but. exert considerable influence when investigating the
mechanical conditions that determine the character and extent
of the deposit. One thing is however tolerably certain,
that a long time must elapse ere the sea-water can dissolve
those calcareous shells. As shown by experiment, they
differ from pure carbonate of lime in yielding much more
slowly to the action of solvents, by reason of their large
proportion of organic substances. Some are disposed to
maintain that carbonate of lime is more readily soluble in
the depths of the ocean owing to the greater amount of
carbonic acid which the water has been held to contain
there. Mr. Tornøe, however, in his Memoir on the
carbonic acid in the Seas explored by the Norwegian
Expedition, has. I think, successfully refuted that assumption.
Sea-water he invariably found to react as an alkali; and
hence its carbonic acid cannot occur free, but must
obviously be combined with oxygen; as regards the proportion
of that constituent, it is about the same in the depths as
at the surface, and the general uniformity in composition
shown by numerous investigations to characterize sea-water,
precludes the probability of any deviation in this respect
occurring throughout the intermediate strata. The power
possessed by sea-water of dissolving carbonate of lime
cannot therefore lie in a greater or less proportion of free
carbonic acid.
The exceptional formation mentioned above as
distinguishing Biloculina clay in some localities, might also be
ascribed to the action of bottom-currents, if sufficient to
intermingle and keep in motion the tine particles of the
deposit. But this, like the foregoing, is a question which
for the present we cannot pretend to decide. Meanwhile,
all samples of water brought up from the bottom were
perfectly clear, without a trace of floating particles.
On referring to the map annexed to this Memoir,
the eastern limit of Biloculina clay will be seen to lie at
a depth ranging from 900 to 1100 fathoms. In several
localities however Biloculina clay is met with nearer the
surface, and on the other hand, in some places it does not
begin to occur till the depth has reached 1100 fathoms.
Between lat. 64° and 68° N., the western limit of the
Biloculina clay extends over a shallower part of the
seabed than farther north. " Thus, for instance, at Stations 54,
96, and 248 it lies at a depth of 600, 805, and 778
’ fathoms. Without the last of these Stations (about 50
geographical miles from land), the curves of depth for 800
to 1000 fathoms (see page 40) make a sudden bend in the
direction of the coast, which they approach within a distance
of 30 geographical miles, and throughout this tract the
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