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Overgan,usleret, der ofte er saa gjennemvævet af disse tine
Kiselnaale, at man ved at berøre den tørrede Bundprøve
faar Huden fuld af dem.
Yi er berettigede til at antage, at Havets fysiske
Forhold maa have en stor Betydning for Dyrelivets Udbredelse
eller Fordeling over Havbunden; især gjælder dette om
Globigerinerne. der som pelagiske Foraminiferer maa være
udsatte for de forskjellige Strømningers Virkning — hvad
enten de nu i clød eller levende Tilstand synker necl i
Slammet. Ved mine kemiske Undersøgelser af
Biloculin-leret har jeg, som senere skal sees, taget Hensyn til disse
Spørgsmaal.
Betragter man forskjellige Prøver af Biloculinleret
under Mikroskopet, vil man finde, at. Blandingsdelenes
Finhed ikke altid er den samme. Maugensteds kan man neppe
selv med eu stærk Forstørrelse adskille de enkelte
Partikler, men i Almindelighed ser man dog en Del krystallinske
Korn, der tildels er af forskjellig Farve. De Heste af disse
er imidlertid farveløse og gjennemsigtige og synes for den
største Del at bestaa af Kvarts. At dette Mineral kan
udgjøre en væsentlig Bestanddel af Dybvandsslamniet. har
allerede Ehrenberg1 paavist ved sine Undersøgelser af tre
Prover fra Atlanterhavets Bund (Dybde: 10,800, 12.000
og 12.900 Fod).
Slammets fineste krystallinske Partikler er i
Almindelighed temmelig skarpkantede; grovere for clet ubevæbnede
Øie synlige Korn forekommer næsten aldrig i Biloculinleret,
men er derimod ikke ualmindelige i Overgangsleret og har
da som oftest en afrundet Form. I det sidstnævnte Ler
ser man ofte talrige Glimmerblade; disse forekommer ogsaa
i Biloculinleret, men er her saa yderst smaa, at ele
vanskelig kan opdages.
Pimpsten eller amorft, vulkansk Glas synes ikke at
udgjøre nogen væsentlig Del af Biloculinlerets
mikroskopiske Bestanddele. I 10 15 Prøver fra forskjellige Partier
af Havbunden fandtes vulkansk Glas blot paa et Par
Stationer. Nogle større Stykker (2x2x2 Cm.) blev
optagne paa Station 40. Her gjordes forøvrigt et
eiendommeligt Fund, der fortjener nærmere Omtale. Sammen med
Pimpstenstykkerne fandtes nemlig i Skraben en Mængde
faste Klumper eller Knoller, der var af forskjellig Udseende
og Art, liggende aldeles for sig selv, ligesom Stene i
Lermassen. De største af disse (6x6x6 Cm.) var af en
meget forskjellig og uregelmæssig Fonn; den haarde og
furede Overflade var tildels bedækket af et tyndt sort Lag,
der væsentlig var dannet af Manganoxyder, medens det
indvendige bestod af en brunrød, porøs Substans, der
indeholdt en temmelig betydelig Mængde vulkansk Glas.
Disse Klumper var temmelig faste, men tillige meget
sprøde og kunde med Lethed brydes istykker; de havde en
1 Berliner acatl. Berichte von 1854. S. ">4, 236, 305, von 185.’.
S. 17:5. Nærmere beskrevet i ■ Microgeologie" von Ehrenberg.
Leipzig 1854.
bers in transition clay, which is absolutely interwoven with
these minute siliceous needles, so. that, on touching the
dried bottom-sample, the hand gets covered with them.
We have reason to believe that the physical
conditions of the sea exert very considerable influence on the
distribution of animal life over its bed: and in particular
as regards Globigerince, which, as pelagic Foraminifera,
must be exposed to the action of currents, in whichever
state they reach the bottom — living or dead; To these
questions, as will afterwards appear, I had due regard when
analysing samples of Biloculina clay.
On examining under the microscope Biloculina clay
from different localities, the fineness of its constituents is
not always found to be the same. In some samples, even
when highly magnified, it is hardly possible to distinguish
the individual particles of which they consist: a number of
crystalline granules, here and there varying in colour, may
however be generally detected with a powerful lens; but
the majority of such are colourless and translucent,
consisting apparently in greater part of quartz, a mineral the
occurrence of which as one of the principal constituents of
deep-sea surface-layers has been already shown by
Ehrenberg,1 who submitted to analysis three samples of such
deposit from the bed of the Atlantic, — depth, respectively
10,800, 12,000, and 12,9.00 feet.
The finest crystalline particles of deep-sea deposit are
as a rule comparatively sharp-edged; coarser granules occur
very rarely if ever in Biloculina clay, whereas in transition
clay such particles, of a. rounded fonn, are not infrequently
met with. The latter deposit is often found to contain
numerous laminæ of mica .schist, which also occur in
Biloculina clay, but so delicate and minute as to be with
difficulty detected.
Pumice or scoriæ does not appear to be one of the
chief microscopic constituents of Biloculina clay. Of 10 to
15 samples from different parts of the sea-bed, scoriæ
occurred in one or two only. A few larger pieces (2x2
X 2°"’) came up at Station 40. where the deposit was found
to be characterized by a peculiar feature, which I must
not omit to record. Along with the fragments of pumice,
but lying apart and imbedded like stones or pebbles in the
clay, the dredge brought up a number of nodules or
concretions, varying in character and appearance. The
largest, measuring 6 X 6 X 6om, were very different and
irregular in form; the hard, furrowed surface had in some a
thin coating of black* oxide of manganese, whereas the inner
portion consisted of ’a brownish-red, vesicular substance,
containing a considerable proportion of scoriæ.
These concretions are comparatively firm, but at the
same time exceedingly brittle; their weight too is very
1 Berliner acad. Berichte von isr.4. pp. ."’4, 236, 305, von 18")")
p. 173. The subject is treated more at large in "Microgeologie"’ von
Ehrenberg. Leipzig I8.r)4.
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