616 



A. HESSELBO 



Lava-clefts. The caves, clefts and cavities which occur every- 



b 



where in the lava-fields contain a Bryophyte vegetation very rich 

 in species. In the broader clefts and in the lava-vesicles (Helgi 

 Jonsson's "Herb-cavities", 1900, p. 90) the bottom is often covered 



Fig. 37. Lava-cleft near Thingvellir (Almannagj;'\). The lava-blocks are 

 quite covered with Rhacomitrium hypnoides. 



with ferns and flowering plants, and especially in deeper clefts, or 

 where the bottom is covered with loose blocks, there is also found 

 a continuous carpet of mosses and liverworts in which Hylocominm 

 spp. (H. proliferum , H. parietinuin , H.loreum, H. squarrosum and 

 H. triquetrum) together with species of Rhacon\itrium, Hijpnnm and 

 Dicranum play a prominent part, and are usually much interwoven 

 with liverworts such as Lophozia lycopodioides, L. quinqnedentata, 

 L. Kunzeana, Cephalozia spp., Alicularia scalaris, Ptilidium ciliare, etc. 



