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4.8
Kysten — ikke er større, end at vi i Overensstemmelse
med tidligere Erfaringer kan tænke os. at Bølgernes
Virkninger forplanter sig helt ned til Bunden.
I Overensstemmelse med de foregaaende Analyser
synes det rimeligt at antage, at Rhabdammina-Leret —
saaledes som vi linder det paa de østligste Stationer - maa
have sin Oprindelse fra stærkt kvartsholdige’ Bergarter.
For at tinde saadanne behøver vi ikke at lede længe i de
omgivende Lande; vi møder mægtige Sandstenlag paa
Nordkysten af Norge, paa Beeren Eiland og Spidsbergen,
ligesom ogsaa talrige Brudstykker af den samme Bergart blev
fundne ved de fleste Dybdemaalinger og Skrabninger i
Øst-havet.
Men selv om vi med nogen Grad af Sandsynlighed
kan tænke os, at denne Bergart har været den oprindelige
Kilde for Dannelsen af Rhabdammina-Leret, saaledes som
vi finder det paa de tvende ovennævnte Stationer, bliver
det imidlertid et andet og vanskeligere Spørgsmaal at
afgjøre, fra hvilken Kant Materialet er hentet, og hvorledes
dette er blevet fordelt over den jevne og grunde Havbund.
Jeg skal her blot indskrænke mig til at nævne, at
den omtalte lille 0 Beeren Eiland har særegne Betingelser
for at kunne forsyne den nærliggende Havbund med stadig
nye Bidrag til dens Afleiringer. Beeren Eiland har
allerede i Løbet af en Menneskealder undergaaet betydelige
Foraudringer ved Isens og Bølgernes ødelæggende
Virkninger. De løse itufrosne Bergslag, hvoraf Øen tildels bestaar,
ligger ved Kysterne blottede for Havet, hvis Kraft her ikke
bliver afdæmpet véd Holmer eller Skjær. Geologen Prof.
Keilhau1 giver i sin Beskrivelse af denne. 0 følgende
Skildring af, hvorledes Ødelæggelsen foregaar: "Ved saadanne
vertikale Revner, og ved de ydre Stykkers derpaa følgende
Fraløsning gaar Øen lidt efter lidt sin fuldkomne
Forsvinden. imøde; allerede i Mands Minde er Kyster hes Forandring
mærkelig, og at slutte efter de ældste Erfaringer, maa
allerede betydelige Stykker være undergangne".
Vi maa saaledes være berettigede til at formode, at
Beeren Eiland stadig kan give Anledning til sedimentære
iV?/danneiser. Hvis Rhabdammina-Leret kan henregnes
blandt saadanne, eller hvis det altsaa er et Depositum af
senere Oprindelse end Nordhavets øvrige Sedimenter, kunde
dette maaske være en Grund for den mindre oxyderte
Tilstand, hvori det befinder sig.
Hvor vi i den vestlige I)el af Nordhavet træffer et
lignende porøst og stærkt sandholdigt Ler. er dette som
oftest af en brun Farve, eller altsaa stærkere oxyderet.
Man kunde altsaa tænke sig. at Slammets Oxydationsgrad
var afhængig af den Tid. i hvilken det har befundet sig i
Havet. Denne Antagelse bestyrkes, naar man ser hen til
1 Reise til Vest- og Østfinmarken samt til Beeren Eiland og
Spidsbergfen.
— at a considerable distance from the coast — is not greater
than will, we know, in conformity with experience, admit
of the influence of the waves being transmitted from the
surface to the bottom.
From the resülts of the foregoing analyses, it would
appear that the origin of Rhabdammina clay, as that
deposit occurs in the most easterly localities of the North
Atlantic, may be traced to the disintegration of quarzitic
rocks, — an assumption borne out by the geological
character of the surrounding countries. Along the north coast
of Norway, and on Beeren Eiland and Spitzbergen, we meet
with vast masses of sandstone: and numerous fragments of
that rock came up when soimding and dredging in the
East Sea.
But even admitting that disintegrated sandstone has
chiefly contributed to the formation of Rhabdammina clay
as found at the two above-mentioned Stations, another and
more difficult question remains to decide from what quarter
the siliceous particles are. derived, and how they are
distributed over the level and shallow bottom.
On this head I shall merely observe here, that Beeren
Eiland has peculiar facilities for constantly furnishing the
adjacent portions of the sea-bed with the material
composing their surface-layer of deposit. Within the memory of
. man, the combined action of the waves and glaciérs have
caused that island to undergo very considerable changes.
The porous, frost-riven rocks of which this island in great
part consists, are everywhere on the coast exposed to the
full sweep of the ocean, no islets or skerries being here to
break its force. The following extract from Professor
Keil-hau’s description of Beeren Eiland1 will show in what
manner the work of destruction is proceeding: — "From
the repeated occurrence of such vertical fissures and the
subsequent dislocation of the outer fragments, the slow but
total demolition of the islapd may be surely foreseen; even
within the memory of man, a remarkable change has taken
place in the coastal outline, and to judge from the oldest
accounts considerable portions of the island must have
already disappeared."
We have accordingly every reason to assume, that
Beeren Eiland, so long as it exists, will still continue the
source of sedimentary neiv formations. Now, regarding
Rhabdammina clay as one of such layers, and therefore as
of later origin than any other of the deposits .distributed
over the bed of the North-Atlantic, this may possibly serve
to account for the low degree of oxidation by which that
. substance is distinguished.
A porous and highly sabulous clay is also met with
in the western tract of the North Atlantic, but its colour
is generally brown, indicating a more advanced stage of
oxidation. ’ We might therefore not unreasonably infer that the
greater or less extent to which a deposit is oxidized mainly
depends on the length of the period during which it has
1 Reise til Vest- og Østfinmarken samt til Beeren Eiland og
Spitzbergen.
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