PRECIPICES AND ROCKS 



shrubs could be seen even on flows which were red-hot only 

 twenty years before, whilst on old lava-fields herbs, shrubs, 

 bushes, trees, and even true woods had developed. ^ 



Yet in Greenland lava-flows dating from 1724-29 are still 

 only covered by crust-lichens and a very few of the stone- 

 mosses ! In Sumatra, on the other hand, the volcano of 

 Tamboro, which in 1815 had entirely destroyed its vegetation, 

 was covered with a fine young wood in 1874 ! ^ The strong 

 heat and abundant moisture of Sumatra favours, whilst the 

 horrible climate of Greenland prevents, the rapid growth of 

 good soil. Just as cities of 20,000 inhabitants can spring 

 up in a few months in the Western United States, whilst the 

 Esquimaux of Greenland have not managed as yet even to 

 live in villages ! 



The full beauty of this gradual colonization and occupa- 

 tion of bare rock and stones only impresses one properly 

 if one tries to trace the stages, but it is an interesting 

 history. 



Near Glasgow one sees great heaps of shale or blaes 

 (generally bldcJcband), which are often mistaken for natural 

 hills. This is or was virgin soil, never occupied by plants, 

 and entirely destitute of leaf-mould or any sort of organic 

 plant-food. 



If one scrambles to the top of one of these heaps, it is easy 

 to see all the details of the occupation. Long underground 

 runners of coltsfoot and of horsetail are climbing up the 

 sides, fringes of creeping buttercup, couchgrass, and other 

 hardy weeds occupy, every year, a little more of the flanks, 

 but, on the top, one very soon finds that the dust of the 

 atmosphere, aided by weathering, has afforded a chance to 



^ Engler, Humboldfs Centenaarschriftt 1889. 

 2 Warming, Lehrbuch der Oekol. Pfl. Geog. 



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