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54
Ved denne Expedition optoges nemlig fra Havbunden
en Mængde Klumper og Knoller, hvoraf enkelte ifølge
Beskrivelsen maa være af en lignende Art som de ovennævnte
fra Station 40. Den betydelige Udfældning af
Manganoxyder. der ved samme Anledning blev paavist i
Havbundens Afleiringer, synes derimod ikke at have noget
Sidestykke i det europæiske Nordhav.
Jeg har forud omtalt, at det brune Ler kun synes
at udgjøre et tyndt Lag paa Havbunden. Hvor denne
begynder at skraane op mod Kystbankerne og nærme sig
til det graa Lers Territorium, finder vi i Særdeleshed ofte
i Bundprøven et underliggende Lag af det sidstnævnte
Sediment. Nedover mod Dybet tiltager det brune Ler i
Mægtighed. og indenfor Biloculinlerets Omraade finder vi
de fleste Bundprøver helt igjennem ensartede. De enkelte
Steder, hvor der ogsaa her findes tvende forskjellige Lag i
Bundprøven og den Mængde af graat Ler. der optoges
med Skraben eller Trawlen, viser at Bjloculinleret er af
en forskjellig, men i det Hele taget ringe Tykkelse. Paa
den Del af Havbunden, der ligger omkring Stationerne 213,
214 og 215 paa et Dyb af over 1700 Favne synes
Bilo-culinleret i Særdeleshed at være meget tyndt udbredt. Paa
Ståt. 215 udgjorde det graa Ler den overveiende Del af
Bundprøven og paa Ståt. 213 fandtes kun Spor af
Biloculinler. Dette graa Underler er meget fint. ensartet og
plastisk, og bliver efter Tørring meget fast og
sammenhængende. Leret indeholder ingen Dyrelevninger og
Kalk-gehalten er kun ubetydelig. Under Mikroskopet viser det
yderst smaa krystallinske Partikler (Kvarts?), der først
træder tydelig frem ved en Forstørrelse af 500—(500 Gange.
De Bundprøver, der blot bestaar af Biloculinler. er
i Almindelighed helt igjennem ensartede med Hensyn til
Udseende og Foraminiferernes Skaller saa jevnt fordelte i
Lermassen, at ethvert Stykke af denne omtrent viser den
samme Kalkgehalt.
Paa enkelte Steder forekommer dog i selve
Biloculin-leret en Lagdannelse, der giver sig tilkjende derved, at
Buudprøvens øverste Del bestaar af et brunt, fint Ler uden
Kalkskaller, medens der under dette findes et porøst Ler
med en Mængde Foraminiferer. Denne Lagdannelse er af
en lignende Art som den, man erholder ved at slemme
Biloculinleret ud i Vand og derpaa lade det afsætte sig.
Ved denne Operation synker alle Kalkskaller tilligemed
andre grovere Partikler tilbunds, medens man øverst faar
et fint kalkfattigt Ler. Det synes rimeligt at antage, at
en lignende Bundfælding allerede kan foregaa i Havet og
bidrage til den ovenomtalte Lagdannelse, men i saa Fald
maa man fristes til at spørge, hvorfor den ikke altid
forekommer i Biloculinleret.
Vi mangler for Øieblikket Forudsætninger til at kunne
besvare dette Spørgsmaal, thi hertil kræves Kundskab om
On that British’ Expedition numerous nodules and
concretions were brought up in divers localities from the
bed of the sea, some of which, to judge from the
description, must have been similar in character to those that
came up on the Norwegian Expedition at Ståt. 40.
Meanwhile, the very considerable proportion of oxide of
manganese determined as a constituent of the deposit in which
the nodules lay imbedded, does not appear to
accompany the occurrence of such concretions in the North
Atlantic.
As previously stated, the brown clay would appear
to constitute a comparatively thin surface-layer. Where
the sea-bed. shelving up to the coastal banks, begins to
approach the province of the grey clay, samples of the
bottom have very frequently an under layer of that deposit.
Downward, in the direction of the depths, the brown clay
increases in vertical extent, and within the limits of
Biloculina clay, most samples of the bottom are found to be
homogeneous throughout. From the few samples which
even here consisted of two different layers, together with
the large quantity of grey clay brought up in the dredge
or trawl. Biloculina clay is however clearly shown to be a
deposit of trifling though variable extent in a vertical
direction. Throughout the section of the sea-bed surrounding
Stations 213, 214. and 215, at a depth of more than 1700
fathoms. Biloculina clay would in particular appear to be
very thinly distributed. At Station 215, the sample
con-’ sisted in greater part of grey clay, and in that brought up
at Station 213, traces only of Biloculina clay were observed.
This grey underlying clay is fine, homogeneous, and plastic. •
and becomes on being dried exceedingly firm and cohesive;
it contains no animal remains and the amount of carbonate
of lime is inconsiderable (1—2 per cent). With the aid
of the microscope, minute crystalline particles (possibly
quartz), may be detected, which do not become distinctly
visible till magnified five or six hundred times.
Samples of the bottom consisting exclusively of
Biloculina clay, are as a rule uniform in appearance throughout,
and the foraminiferous shells so regularly distributed in
the deposit, that every part of it has well-nigh the same
proportion of lime.
In certain localities, however, the surface-layer of
Biloculina clay was found to be exceptional in formation:
a fine brown clay without calcareous shells constituted the
upper part of the sample, whereas the under layer
consisted of a porous clay containing great numbers of
Foraniinifera. This formation is similar to that of the deposit
left on washing Biloculina clay, during which operation the
calcareous shells and other coarser particles sink to the
bottom, leaving a fine clay, containing very little lime, as
the upper layer. Some such precipitating process may not
improbably be going on in the waters of the ocean and
thus contribute to the formation described above; but if so.
the question naturally arises why the latter is not an
invariable characteristic of Biloculina clay.
For the full investigation of this subject we are at
present in want of the requisite data, assuming as it does
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