372 



NA TURE 



[August 1 6, 1883 



berg's val del bove, which constitutes the snow-field for 

 the largest of its glaciers, that jut out from the north side 

 of the mountain. On the east side, too, are seen pro- 

 minent ribs, all of which intersect the neve's of the east 

 side ; towards the south and west, however, the surface 

 of the outer cone would appear to be remarkably smooth, 

 at the edge of the crater only being furrowed with shallow 

 depressions between the jags. The base of Mount 

 Beerenberg shelves towards the west, south-west, and 

 north-east, with a comparatively gentle incline, either to 

 the water's edge or the low-lying shore; towards the 

 north and east, however, the descent at the coast is very 

 abrupt, exhibiting precipices 1000 feet high. In several 

 places the base of the mountain is intersected by deep 

 ravines, through which the glaciers find a passage to the 

 sea. 



"The height of the southern part of the island cannot 



be compared to that of the northern. The southern land 

 constitutes a wide plateau, which, in a south-easterly and 

 southerly direction, exhibits numerous precipices along the 

 coast, but, towards the north-west, has extending before it 

 a low-lying foreland, less than 300 feet above the sea. 

 The height of the plateau I estimated at 1000 feet. Rising 

 above this tableland are seen several summits ; the 

 loftiest, which has apparently a conical form, and may 

 therefore be of eruptive origin, can hardly attain an 

 altitude of 1600 feet above the sea-level. 



"The low middle tract of the island, which is built up 

 of compact masses of lava, and bears numerous eruptive 

 craters, has at its lowest point an elevation of only 200 

 feet, or perhaps even less, whereas the crater summits 

 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. 



Fig. 4. 



" 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 appear- 

 ance, 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 Guinea Bay ; others are 

 composed of layers of tuff, tuff-conglomerate, and com- 

 pact masses of lava, as the Fugleberg, and 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 direc- 

 tion 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 W.N.W. to E.S.E. ; 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 



