184 6 



the light-coloured sections to the right represent the position of the solfataras. 

 The light colour is chiefly to be attributed to the sulphurous deposit from the 

 springs. We examined here the gases from two springs, viz. Krafla No. 1 ', imme- 

 diately to the east of the northern lake, and Krafla No. 2, to the north-east of the 

 southern lake. The springs were identical in outward appearance, both being small 

 pools of turbid water, with strong gaseous exhalations. Their altitude above the 

 surface of the lakes was 10 cm., while they were 615 m. above the level of the sea. 

 The temperature of the water in the twin lakes was 11.5° C. on the surface; the 

 surface temperature of the water in Helvfti, taken at the same time, was 14°; whilst 

 the temperature of the air was 3°. These observations of temperature seem to 

 indicate that the water in Helvi'ti continually receives considerable heat from the 

 interior of the earth, in spile of the fact that it is impossible to see the least sign, 

 on the surface of the lake, that there is at present any connection between the 

 water in Helviti and the torrid interior of the earth. Helvfti probably receives 

 most of its heat by conduction. The twin lakes apparently receive no little heat 

 from the springs on their banks. 



Ndmafjall is a palagonitic mountain of which the highest point, according to 

 the altitude we took, is 500 m. above sea-level ; Johnstrup estimates its height at 

 498m. Here the palagonitic tuffs are much disintegrated; in many places the loose, 

 mouldering tuffs form a stratum more than a metre thick. Near Namafjall there 

 is a great profusion of solfataras with considerable sulphurous deposit. Most of 

 the solfataras are situated right up on the mountain, on its eastern slope. Smaller 

 groups of solfataras are also to be found at Bjarnarflag, a tufa plain to the west 

 of Namafjall. 



To the east of Namafjall is, on the other hand, a group of hot springs con- 

 sisting of from 8 to 10 large ugly mud pools (360 m. above sea-level). These sloughs, 

 which stretch in a line from north to south, are bounded on the east by a field 

 of lava; it appears that the mouldering tufa, which descends from the eastern side 

 of Namafjall, has forced the outlet of the springs towards the lava. We examined 

 the gases from three places in this group of sloughs. 



The gas sample numbered Namafjall No. 1 is from the largest slough in the 

 group, the position of which is to the extreme north-west (Plate I, h). Namafjall 

 No. 2 is taken from a smaller cavity by the edge of the lava, to the east of No. 1. 

 Namafjall No. 3 comes from the slough second in point of power; it is situated a 

 little south of the centre of the group. 



Besides the above mentioned sloughs, we saw some in a groove on the east 

 of Namafjall, high up at the top of the mountain. These springs were surrounded 

 on all sides by solfataras, so that we could not approach them, but they appeared 

 to be very active. The southern part of Namafjall is flat on top, and in the centre 

 of this plain is a little isolated group of sloughs, consisting of 3 springs ; the gas, 

 marked Namafjall No. 4, is taken from this group, (490 m. above sea-level). 



1 Cf. Part III, Table 1. 



