740 



The algæ which cover the walls farther in the cave are either 

 such Hitoral algæ as would be found in the open air on the beach 

 in cracks and clefts or otherwise sheltered from strong light, or 

 sublittoral algæ which here approach the surface of the water as 

 the light grows fainter. Some of the latter may even be found 

 at such a height, that they are dry at low tide. Among these there 

 are several Florideæ which are usually only found at a great depth 

 in the open sea. When rowing into such a cave, a condensed but 

 exact piclure is obtained of the algæ -vegetation that grows on a 

 vertical rock in the open air, moving from the top downwards. 

 Immediately at the entrance there are of course littoral algæ, but 

 they soon disappear, as before mentioned, and so does the Alaria- 

 association. The Laminaria hyperborea is found a little farther in, 

 but it also soon disappears, and only Florideæ are left. 



By closer observation of the algæ-vegetation , we find that, as 

 mentioned above only a few specifically littoral algæ grow^ here. The 

 alga which is most widely distribuled and found at the greatest 

 height is Rhodochorton Rothii. Far stretching vegetations of it like 

 a dense, low, brownish-red felt cover the walls and ceilings of the 

 caves (cf. the 7?/io(yoc/jo/7o/j-association, page 718). Even in the mighty 

 caves on Troldhoved it is certainly this alga which gives the more 

 than 50 feet high rocky vaults their redish hue. At the entrance of 

 the caves and close to the level of the sea it grows on the rock 

 in small, firm lumps of the size of a pea. 



From about the highest water mark downward, a dense, almost 

 blackish covering of Phimaria elegans is often found in the caves. In 

 the Færoes I have only met with this alga in these piaces. Toge- 

 ther with Phimaria, a dense covering of Delesseria alata, Ceramium 

 ruhriim, Polysiphonia iirceolata, and others, are also found. They 

 form a dark red, tangled vegetation which is often joined by 

 Cladophora riipestris closer to the entrance of the cave. In a 

 cave on the northern side of Kvalbofjord on Sydero, a low, red 

 covering of a small Phijllophora (8, p. 859) was found, some way into 

 the cave. A little above the lowesl water mark, the elegant little 

 Caltithanmion scopulornm is abundant, and Callithamnion arbnscula 

 may also sometimes be found in the caves. It partly changes its 

 appearance here, becoming less ramified and of a lighter reddish 

 colour. Whilst the Corallina is most often the subvegetation at the 

 entrance of the caves, it is replaced by the Phymatolithon poly- 

 morpham farlher into the cave. At the entrance of the caves, for 



