THE BKYOPHYTA OF ICELAND 609 



bottom of the cave there grew Timmia austriaca, Brijiuu ventricosum, 

 Brachythecium rimilare, Tluiidinm delicatulum and Marchantia poly- 

 inorpha, and at the entrance to the cave where the water was drip- 

 ping down, il//?w/ undulatum occurred. The upper part of the 

 walls and the roof were covered with Blepharostoma trichophyllum, 

 Amblystegium Sprucei, Metzgeria fnrcata and Radnla complanata, and 

 in the better-lighted part around the entrance, the cave was covered 

 with Homalothecium sericeum and Orthothecium intricatum. 



The Southern Slope of Eyjafjall consists partly of basalt 

 and partly of tuff-layers. The numerous rivers which issue from 

 the Jokull usually ilow at the bottom of deep, narrow clefts in the 

 tuff-layers. 



v' 



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

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

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

 few places, the water usually rising from the bottom up to the 

 perpendicular rock-wall. The sides are, as a rule, rather damp, 

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

 faces. The Bryophyte vegetation is extremely luxuriant, 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 debris at the base of the cleft-sides : 

 Hylocomium spp. f especially H. sqnarrosuin and H. proliferum) , Hyp- 

 nnm stellatum, Acrocladiam cuspidatum, Climacium dendroides, Eu- 

 rhynchium Stockesii, Thuidium tamariscinum, Mniiun undiilatum, M. 

 pnnctatum, Timmia austriaca, Marchantia polymorpha, etc. In the 

 numerous open caves and under overhanging rocks, a characteristic 

 vegetation of Marchantiacece was found. Preissia commntata (fr.) and 

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

 boulia hemisphcerica occurred abundantly in several places, and was 

 also_fruiling. Here Enrhijnchiiun Swarlzii also was at home, espe- 

 cially on the less damp rock-faces, while Thamnium alopecurum 

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

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

 Rhynchostegium rusciforme, Brachythecium rivulare, Haplozia cordi- 

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

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

 worts, unusually rich in species and composed of Hypiuun filicinum 

 (in masses), H. falcatnm (in masses), H. molluscum (in masses), Philo- 

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



