THE BRYOPHYTA OF ICELAND 609 



bottoni of llie cave Ihere grew Timmia aiistriaca, Brijum ventricoHum, 

 Hracliijtheciiini rivulare, Tlmidiniu delicatiilnm and Marchanlia pohj- 

 iiiorplm, and at the cntrance to the cave where Ihe water was drip- 

 ping down, Mniiim iindulatiim occurred. The upper i)art ol" tlie 

 ^valls and the roof were covered with Blepharostoma trichophijllum, 

 Amhiysfegiiim Sj)nicei, Metzgeria fiircata and Radala complauata, and 

 in the l)ettei-lighted part around the entiance, the cave was covered 

 with Homalotheciiim sericeum and Orthothcciiim intricaium. 



The Southern Slope of Eyjafjall consists partly of basalt 

 and partl}'^ of tuff-laN'ers. The niimerous rivers which issue from 

 the JokuU usually flow at the bottom of deep, narrow clefts in the 

 tufT-layers. 



Holtsa, which is a ghicier-river of rather considerable size, 

 flows for ahnost its entire course, from the Jokull down to the low 

 land, at the boltom of deep clefts which are accessible only in a 

 few [)laces, the water usually rising from the boltom up to the 

 perpendicular rock-wall. The sides are, as a rulc, ralher damp, 

 and the water from the slopes above oflen flows down the rock- 

 faces. The Bryophyte vegetation is extremely luxuiiant, and the 

 sides of the clefts are, for considerable distances, covered with enor- 

 mous carpets of mosses and liverworts. The following species 

 covered the fallen blocks and débris at the base of the cleft-sides: 

 Hylocomiiim spp. ("especially H. sqiiarrosum and H. proliferum), Hyp- 

 iiiim sti'llcdum, Acrodadiiim cnspidatiim, Climacium dendroides, Eu- 

 rhynchium Stockesii, Thnidium tamarisciniim, Mniiim iindnlatum, M. 

 piinctatnm, Timniia aiistriaca, Marchaniia polymorpha, etc. In the 

 numerous open caves and under overhanging rocks, a characteristic 

 vegetation of Marchantiaceæ was found. Preissia commutata (fr.) and 

 Fegatella conica covered the sides with metre-broad mats, and Re- 

 boiilia hemisphærica occurred abundantly in several piaces, and was 

 also fruiling. Here Eurhynchiiim Swartzii also was at home, espe- 

 cially on the less damf) rock-faces, while Thamniiim alopeciirum 

 preferred spots where the water was flowing down. Where slream- 

 lets were running from above down the rock-sides, there grew 

 Rhynchostegiiim rnsciforme, Brachytheciiini riinilare, Haplozia cordi- 

 folia and, lowermost, Thamniiim, while the more or less damp rock- 

 faces were covered with a variegated carpet of mosses and liver- 

 worts, unusually rich in species and coiuposed of Hypniim filiciniim 

 (in masses), H. falcatiim (in masses), H. molliisciim (in masses), Philo- 

 notis tomentelia, P. fontana (in abundance), Mninm serratum, M. stel- 



