578 A. HESSELBO 



geysirs and mud pools the ground is iisually quite bare as far as 

 the boiling water and the mud are al)le to spurt. 



Near the boiUng basins which occur in great number and gene- 

 rally have a diameter of 2 — 4 metres, the ground forms, as a rule, 

 a slope on the one side with an angle of 25° — 40°, whilst on the 

 opposite side the water flo^vs down a gentle slope which stretches 

 as far as to the river. The ground for the first 10 — 20 cm. of this 

 slope, which corresponds approximately to the different water-ievels, 

 is of a greyish-white colour and quite bare of vegetation. Then 

 comes a helt of varying breadth formed of liverworts which, next 

 to the water, are black or of a brownish black, above this of a 

 reddish-brown or brownish-green, and at the top, green. This liver- 

 wort-carpet was everywhere composed of Gymnocolea inflata, Haplo- 

 zia creniilata, occasionally also Aliciilaria scalaris f. riifescens and at 

 the top Cephalozia bicnspidata. The temperature under the moss- 

 covering was on an average 20° — 25°. 



Polytrichum commune grew scattered in the liverwort carpet, 

 from which itsbluish-green tops protruded several centimetres, but frequ- 

 entlyitalso formed large growths above the liverworts, partly interwoven 

 with the latter. Only very few phanerogams were able to grow 

 there, usually only flowerless specimens of Viola palustris, the short- 

 stemmed leaves of which rested on the liverwort carpet. Besides 

 the above-mentioned Bryophyta several others were found on the 

 warm claye}' flåts, although far more scantily. Anthoceros punda- 

 tus, Fossombronia Diimortieri, Blasia pusilla and Archidiiim phascoides 

 grew liere and there. In several piaces Oligotrichiim herctjuiciim 

 occurred in tufts a few mm. high, and in one single locality Alicii- 

 laria geoscijpha and Aongstræmia longipes were found in company 

 with it. On warm ground between loose blocks of rock, at an alti- 

 tude of about 260 metres, the following were found among others: 

 Polytrichum commune, Hylocomiiim loreiim, Plagiothecium elegans 

 and Diplophylliim albicans. 



In the neighbourhood of the farm Reykirfoss, on the western 

 side of the river, and at the edge of the lava lield, there is a rather 

 large spring with pure water of a temperature of about 37°. Here 

 the blocks of stone in the water were quite covered with Pellia 

 Neesiana, in the tufts of which Veronica Anagallis had taken root. 



Where the boiling water flowed over the slightly inclined slopes, 

 it deposited greyish-white siliceous sinter, upon which grew blue- 

 green algæ as soon as the water had cooled down to 60° — 70°. The 



