888 



conditions for vegetation, and that heie it will reach its fullest de- 

 velopment when the edaphic conditions are also favourable. 



This distinction between the north and south slopes is a result 

 of the sun's influence, or, in other words, the combined eftects of 

 the varying degrees of light, heat, and the amoiint of soil-moisture 

 resulting from the exposure. It is a fundamental difference which 

 we shall have occasion to refer to frequently in the chapter on 

 plant- formations. 



2. Edaphic factors. 



a. Nature of the soil. The geological slructure of the Færoes 

 is very uniform (see geological account Vol. I, pp. 24 — 31). The 

 islands consist entirely of basalt laid down in almost horizontal 

 beds separated by thin strata of tuff and clay; on Sydero and 

 Myggenæs the clay includes thin layers of coal. Both tuff and 

 clay have originated from the basalt, hence this rock alone need 

 be considered when dealing with the chemical composition of the 

 Færoese soil. 



Mr. O. B. Boggild has drawn my attention to an analysis of 

 Færoese basalt^, which states that it should contain 10, i6 p. cent CaO. 

 Although this is the only definite statement available, Mr. Boggild 

 still regards it as a fair estimate of the probable percentage all over 

 the Færoes, since it is the amount found in most basalts, and they 

 are fairly uniform. This is a high percentage of lime compared 

 with the 1 — 2 p. cent in common granite, and piants need have no 

 lack on this account. On the whole, basalt must be regarded as 

 producing a fair soil for piants, partly because of its chemical com- 

 position, and partly because of its comparatively rapid decay. 



The basalt on weathering forms a reddish-brown soil, of fine 

 texture. The process of disintegration is most noticeable on the 

 mountains, where the soil is more or less free from vegetation, and, 

 if one may judge by personal observations, the weathering proceeds 

 always very rapidly there. The numerous mountain-plateaux are 

 covered as a rule with loose shattered flakes of basalt, with here 

 and there a block falling into fragments, and one rarely sees large 

 exposures of solid rock. The finer disintegrated particles soon 

 settle down, among the coarser material, or they are transported 

 by wind and water, to collect again in sheltered nooks, in cracks 

 and crevices, etc. The frequent and abrupt changes between thaw 



^ Durocher in Annales des Mines, 19, 1841, p. 559. 



