66 



Vulkansk Sand og Sandler. 



Øen Jan Mayen er som bekjendt af vulkansk Oprin- 

 delse. Den stærke lokale Hævning, der har foraarsaget 

 dens Dannelse, giver sig tydeligst tilkjende paa Nordkysten, 

 hvor det egentlige Hovedkrater — den 6000 Fod høie 

 •'Beerenberg" — lindes. Her træffer vi et Braadyb af 

 1 1 ii 10 Favne i en Afstand af omtrent 2 Mile fra Øens 

 nordligste Punkt. Paa Øst- og Vestsiden af Øen skraaner 

 Kysten mindre brat ned mod Dybet. Ved de talrige Dybde- 

 maalinger. som Expeditionen her har foretaget. befandtes 

 alle Bundprover. der var optagne paa mindre Dyb end 600 

 Favne, at beståa af et graasort fint Sand eller Sandler, der 

 indeholdt talrige Brudstykker af den basaltiske Lavas Mine- 

 raler: Olivin. Augit. Hornblende. Disse forekom ofte med 

 vel uddannede og vel bevarede Krystalflader. 



Det vulkanske Sandler viser sig under Mikroskopet 

 ;it indeholde en Mængde forskjelligfarvede krystallinske Korn, 

 der væsentlig bestaar af de ovennævnte Mineraler, især er 

 den grønne Olivin meget fremtrædende. Forovrigt ser man 

 ogsaa en Del sorte metalglindsende Korn. der ved Hjælp 

 af Magneten lader sig udtrække af Bundproverne. Disse 

 synes i det Hele tåget at indeholde de samme Mineraler — 

 i tint fordelt Tilstand — som dem der forekommer i de rige 

 Sandleier langs Jan Mayens Kyster. Dette sorte Sand er 

 dannet af temmelig grove Korn af Lava, Tuf, Olivin. Feld- 

 spath, Augit, Hornblende og Magnetjern. 



Af det sidstnævnte Mineral fandt jeg i Sandet ved to 

 Bestemmelser 26 pCt. og 29 pCt. 1 



Fra disse Sanddynger, der ligger ubeskyttede for Bøl- 

 geme langs Øens aabne Kyster, maa der stadig kunne føres 

 nyt Materiale ud til den nærliggende Havbund. 



I Syd for Jan Mayen synes der ifølge tidligere Lod- 

 skud at være grundt Vand (100 Favne) indtil en Afstand 

 af omtrent 15 Mile fra Øen. 



Her har den norske Expedition imidlertid ikke fore- 

 taget nogen Dybdemaaling, og jeg tør derfor ikke indestaa 

 for Piigtigheden af de Grændser, jeg paa Kartet har op- 

 trukket for det vulkanske Lers Udbredelse søndenfor Jan 

 Maven. 



I Bundproverne fra Kysten af denne findes næsten 

 ingen Dyrelevninger, og Leret indeholder kun Spor af kul- 

 sur Kalk. 



1 Professor Carl Vogt, der i 1863 gjæstede Jan Mayen, hårogsaa 

 underkastet dette Sand en Undersøgelse, ved hvilken han fandt 21.6 

 pCt, Magnetjern. Nord-Fahrt entlang der Norwegischen Kiiste, aach 

 dem Nordcap, den Cnseln .lim Mayen und Island, unternommen vim 

 hr. Georg Berna 1863). 



Voleanic Sand and Sabulous Clay. 



The island of Jan Mayen is. as well known, of vol- 

 eanic origin. More especially on the north coast, have the 

 prodigous forces whereby the ocean-bed vas upheaved in 

 this locality of the North Atlantic, left evidence of their 

 bygone action; there lies Mount Beerenberg, the princi- 

 pal crater — 6000 feet above the level of the sea. About 

 2 geographical miles from the most northerly extremity of 

 the island we meet with a depth of 1000 fathoms. Off 

 the eastern and western shores, the bottom is found to 

 shelve less rapidly down to the depths. All of the numer- 

 ous samples collected on the Expedition throughout this 

 tract from depths of less than 600 fathoms, consisted ex- 

 clusively of a dark-grey sand or sabulous clay, containing 

 fragments of basaltic lava, as olivine. augite, hornblende. 

 Many of these bad well developed and well preserved cry- 

 stal faces. 



The voleanic sabulous clay. when examined under the 

 microscope, is found to contain a great man) - differently 

 coloured crystalline particles, consisting chiefly of the above- 

 meutioned minerals, in particular green olivine. For the 

 rest, numerous black granules of metallic lustre are also 

 observed. which. with the aid of a magnet, may be extracted 

 from the clay. They would appear to consist in greater 

 part of the same minerals — in a state of minute sub- 

 division — that occur in the sand forming extensive banks 

 on the coast of Jan Mayen. This black sand is composed 

 of comparatively coarse particles of lava, tuf, olivine, feld- 

 spar, augite, hornblende. and magnetite. 



The last of tliese minerals I found, from two deter- 

 minations, to constitute respectively 26 per cent and 29 

 per cent of the sand. 1 



These sand-hills, stretching as they do along the ex- 

 posed shores of the island, must obviously at all times con- 

 tribute to the distribution of deposit over the adjacent 

 parts of the sea-bed. 



South of Jan Mayen -- as shown by the results of 

 former soundings — comparatively shallow water (100 

 fathoms) extends about 15 geographical miles from the coast. 



( hi the Norwegian Expedition, the depth was not 

 measured in this locality. and I cannot therefore answer 

 for the accuracy of the limits I have traced on the map 

 to mark the distribution of the voleanic clay south of the 

 island. 



Very few. if any. animal remains are found in samples 

 of the bottom from the coast of .lan Mayen, and the deposit 

 contains traces only of carbonate of lime. 



1 Professor Carl Vogt, who-visited Jan Mayen in 1863, has also 

 submitted this sand to analysis: ln- found 21.6 per cent ni' magnetite. 

 (Nord-Fahrt entlang der Norwegischen lviiste, nach dem Nordkap, den 

 [nseln .Tan Mayen und Island, untcrnoniinen von Dr. Georg Berna 

 1863.1 



