578 A. HESSELBO 



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

 the boiling water and the mud are able to spurt. 



Near the boiling 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, \vhilst on the 

 opposite side the water flows dow r n 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-levels, 

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

 comes a belt 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 crenulata, occasionally also Alicularia scalaris f. rufescens and at 

 the top Cephalozia bicnspidata. The temperature under the moss- 

 covering was on an average 20 -25. 



Polytrichnm commune grew scattered in the liverwort carpet, 

 from which its bluish-green tops protruded several centimetres, but frequ- 

 ently it also 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 clayey flats, although far more scantily. Anthoceros puncta- 

 tus, Fossombronia Dumortieri, Blasia pusilla and Archidium phascoides 

 grew here and there. In several places Oligotrichnm hercynicum 

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

 laria geoscypha and Aongstrwmia 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, Hylocomium loreum , Plagiothecium elegans 

 and Diplophyllum albicans. 



In the neighbourhood of the farm Reykirfoss, on the western 

 side of the river, and at the edge of the lava field, 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 w r ater flowed over the slightly inclined slopes, 

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

 green algse as soon as the water had cooled down to 60 -70. The 



