Soil-Makers 33 



name of mould, which will support plants of quite 

 large size. These are followed by dwarf shrubs, whose 

 roots help on the work more rapidly ; and in a century, 

 more or less, the stream of lava is usually converted 

 into soil fit for the planting of vineyards and gardens. * 



Lichens attack not only lava, however, but also 

 granites, slates, and even hard crystalline quartz-rock, 

 wherever there is sufficient moisture. No rock is 

 proof against them ; almost any climate suits them, 

 hot or cold, moist or dry, and they are the last signs of 

 vegetation to be lost sight of by the mountaineer as he 

 ascends towards the region of perpetual snow and bare 

 peaks, whither even they are unable to follow. But 

 they flourish best and do most work where there is 

 moisture. 



They quickly make their appearance upon any 

 freshly exposed surface of granite, though we may 

 often need a microscope for their detection. In one 

 instance, at least, however, their brilliant colouring and, 

 what is more unusual, their sweet scent betray them. 



The so-called Violet-stone found on the summit of 

 the Brocken is nothing but bare granite, covered with 

 a film of what looks like scarlet dust, which smells like 

 violets, especially on being rubbed. It looks so per- 

 fectly harmless, that one can hardly believe it possible 

 it should affect the solid granite in any way. Yet it 

 does; to a very small extent, indeed, but just sufficiently 

 to prepare the way for two large brOwn lichens, which 

 are the next to make their appearance ; and then the 

 work proceeds more rapidly in the way already 

 described, until at last tall pine-trees rear their heads, 

 and find sufficient food and foothold, where but a few 

 years before there was nothing but a bare surface. 



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