184 OLAF GALL0K 



highlands, are either very poor in, or entirely devoid of, phanero- 

 gams, and between the stones mosses idriinmia hijpnnides) chiefly 

 occur, in part together with lichens; this will, however, be discussed 

 more fully under the vegetation of the moss-carpets of the island. 



The Gravelly flats in the lowlands bear a scanty vegetation 

 of herbs, (see e. g. Thoroddsen in vol. I, p. 326 of the present 

 work; Jonsson's lists are exhaustive, but, like Thoroddsen, he 

 makes no mention of linding lichens). 



In river-gravel in the lowlands Chamcenerium is common. The 

 river-flats are occasionally inundated in spring, and are devoid of 

 lichens. 



The gravelly flats of the plateau are "the parts of the rocky 

 flat poorest in plants" (Jonsson). Here and there grow Luzula 

 spicata, Oxyria diyyna, (lerastium alpinnm, Silene acaulis, Arabis 

 />elrcea, Galium silvestre, Saxifraga ccespitosa, etc. Moss-cushions 

 (Dicranum falcatum) occur also, and, - - as "collars" around larger 

 stones, - - small carpets of (irinuuia hypnoides intermixed with lichens 

 (C.clraria islaiidica and CAadoma) and phanerogams; this will be 

 mentioned more fully under the moss-vegetation. The gravelly flats 

 which I traversed just below the summit of the mountain "Sulur, 

 near Eyjafjordur, were still, on the 5th of July, supersaturated with 

 the down-trickling snow-water, and were quite bare of vegetation. 



Sandy flats. Several kinds of sandy flats of various geological 

 origin occur, partly in the lowlands, and partly in the highlands. 

 Many of them are quite bare of plant-growth along such great tracts, 

 that days intervene before a few individuals are again met with. 

 The commoner types of sandy flats are: beach-sand (with a halo- 

 philous herb-vegetation), which is devoid of lichens (owing to its 

 contents of chloride of sodium); Jokul-sand (which is often inundated 

 by Jokul-rivers) either devoid of, or with a very poor, herb-vegeta- 

 tion, and without lichens (on account of inundations possibly fol- 

 lowed by drifting sand); and lastly tracts of blown sand (Sander) 

 of various origin, but more or less wind-affected on the surface by 

 frequent and violent sand-storms. The diflerent kinds of sand men- 

 tioned here are devoid of lichens, owing to three essentially different 

 reasons: (1) the occurrence of chloride of sodium in the soil (beach- 

 sand), (2) frequent inundations (the sandy tracts below the Jokuls) 

 or (3) drifting sand, (in the sandy tracts of the plateaux and else- 

 where). 



I traversed, in several places, such extensive sandy tracts, as 



