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150 å 200 Meter. ’ Fugleberget er maalt til 150 Meter.
Ægøen anslaaet til c. 150 Meter.
Beerenbergs Basis er, som paavist af Carl Vogt. bygget
af Lavalag og tildels Tuflag, der synes at have flydt eller
være kastet ud af det store Central-Krater, sandsynligvis
førend dette havde opbygget den øvre Askekegle. Af
lignende Bygning er Øens Midtparti og efter Udseendet at
dømme ogsaa den sydlige Del. Ovenpaa denne store
sammenhængende Lavamasse staa en Mængde smaa Sidekratere,
der for en stor Del have bevaret en udpræget konisk Fonn.
Saadanne ere Krater Sars, Krateret øst for Sydbræen.
Kraterne Esk og Vogt, Kraterne Danielssen og Blytt og
Kraterne ved Guineabugten. Forstyrrede i sin Form ere
Fugleberget paa Vestsiden og Ægøen paa Østsiden, idet
begges ydre Kraterrand er opslugt af Havet. Nogle af
Sidekraterne ere byggede af Lava og have udsendt
betydelige Lavastrømme, som Vogt, Esk,. nogles Top er bygget
af løse udkastede Masser. Slakker og Aske, Rapilli. som
Kraterne ved Mary Muss Bugten, ved Guineabugten, andre
af Tuflag, Tufconglomerater og faste Lavalag, som
Fugleberget, og atter andre af Aske alene, som Ægøen og Berna.
Den vulkanske Hovedspalte, hvorpaa Jan Mayen er
bygget, gaar aabenbart efter Øens Længderetning, efter
Heklalinien. Men Sidekraternes Gruppering synes at give
en Antydning af, at der har været Tverspalter i Retningen
WNW.—ESE. Vi have nemlig i denne Retning, som det
synes, flere Rader af Sidekratere, saasom Esk—Vogt—Berna.
Fugleberg—Egø, Hoyberg—Krater ved Fyrtaarnet (?).
Eidet et Tilfælde, at Endekrateret mod SE. i de to første
Rækker, Berna og Ægø, kun have udkastet Aske?
Af Dale gives der paa Jan Mayen ingen af større
Længde; de større Dale paa. Nordlandet ere fyldte af
Bræerne og Sydlandet synes at være meget lidet indskaaren
af Dale. Af Bække ere kun faa iagttagne.
Karakteristiske for Jan Mayens Kyst ere de paa mange
Steder opstaaende Klipper i Havet, hvoraf vi ovenfor have
nævnt flere. De ere vistnok for største Delen Rester af
Lavastrømme, der ere gaaede ud i Havet.
Jan Mayens Kyster ere. som ovenfor berørt, paa
mange Steder meget bratte og høje. Paa andre Steder er
der et lavt Forland, bestaaende af Lava, dækket tildels
med Sand. Dette Forland, som paa Kartet har sin
særegne Betegnelse, ligger tildels saa lavt. at det er dækket
med Rækved. Låve Strender, af Sand. ere ogsaa
mangesteds tilstede, og indeholde store Mængder af Rækved.
Ivjæver og. Hvirvler af Hval. Vraggods og opkastet Tang.
reach a height of ’400 to 600 feet. The altitude of
Fugleberg we found by observation to be 490 feet : that of Egg
Island was estimated at 400 to 500 feet.
As shown by Carl Vogt, the base of Mount Beerenberg
is composed partly of layers of lava, and partly of layers of
tuff, that would appear to have flowed or been discharged
from the great central crater previous to the formation of
the upper cone of ashes. The middle tract of the island
exhibits a similar structure, and to judge from its
appearance, also the southern part. Above this stupendous mass
of lava rise a number of small parasitic craters, the greater
part of which have retained a conical form. Such, for
instance. are Sars’s crater, the crater east of the southern
glacier, the Esk and Vogt craters, Danielssen’s and Blytt’s
craters, and the craters in the vicinity of Guinea Bay.
Fugleberg on the west coast and Egg Island on the east,
are no longer conical, the outer edge of the crater having
given way and fallen ’into the sea. Some of the parasitic
craters are built up of lava, and would appear to have
sent forth considerable currents, as the Vogt and Esk
craters; the summit of others consists of loose erupted masses,
cinders, and ashes (rapilli). as the craters in the vicinity
of Mary Muss Bay and Guiuea Bay; others are composed
of layers of tuff, tuff-conglomerate and compact masses of
■ lava, as the Fugleberg’ ånd others again of ashes alone, as
Egg Island and the Berna crater.
The chief volcanic fissure in which Jan Mayen Island
is built, must obviously extend in the longitudinal direction
of the land, parallel to the volcanic line of Mount Hecla.
Meanwhile, the grouping of the parasitic craters would
seem to intimate the existence of transverse fissures running
from WNW. to ESE.; for in .that direction there are,
apparently, several rows of parasitic craters, as the Esk,
Vogt. Berna. the Fugleberg and Egg Island. Hoyberg and
the crater in the vicinity of the "pilot-boat" (?). Must we
regard it as mere accident that each of the terminal
craters towards the south-east in the two first rows should
have discharged ashes alone?
Jan Mayen has no valleys of considerable extent; the
large ravines in the northern part -of the island are filled
with glaciers, and the southern land would appear to be
but little intersected by vales or ravines. Of brooks or
rivulets, very few have been observed.
A characteristic feature distinguishing the coast of
Jan Mayen, are the fantastic-shaped rocks that in many
places rise abruptly from the sea, of which we have
mentioned several. They are no doubt in greater part
fragments of laVa detached from currents that had flowed into
the sea.
The coasts of Jan Mayen are, as previously stated,
in many places lofty and precipitous. In some localities,
however, there is a low expanse of foreshore consisting of
lava, partially covered with sand. This foreshore, which is
separately marked on the Map, lies so low in places as to
be covered with driftwood. Some localities, too. exhibit a
low sandy beach, bestrewn with large quantities of driftwood,
the jaws and vertebræ of whales, bits of wreck, and sea-weed.
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