THK BRYOPHYTA OF ICKLAM) 



601 



ing to a height of several hundred metres, right up lo the plateau 

 on the mountain top, but usually divided inlo numerous steps, 

 consisting of shelves or ledges of varying breadth. The rock-face 

 is here and there intersected by dee}) fissures and clefts, excavated 

 by the down ward -flowing water, which partly drains away in 



Fig. 29. Face of basalt rock (E. Iceland). Everywhere in the crevices small, black, moss- 

 cushions (Andrecea. l)icntiwn>cini(i i-rispula and (irinunid spp.). 



these channels, partly spreads over the ledges and from thence 

 flows down the rock-faces or penetrates into the crevices of the 

 rock, and then reappears once more further down. Consequently, 

 the conditions pertaining to moisture vary greatly, and therefore 

 the moss-covering also. As some examples will best show the com- 

 position of the latter, the following are given: 



1. Esja, low damp rock- face just above the slope: 



The Botany of Iceland. Vol.1, part. II. 39 



