CHAPTER VII. 



DUST-MAKERS VEGETABLES AND ANIMALS. 



Lichens the first Soil-makers - How they eat into the Rocks Vegetable 

 Acids Roots, their Length and Number Minerals required by Plants 

 Flint in Grasses, Dutch Rushes Mechanical Power Burrowing 

 Animals, Worms, Ants, Marmots, Birds, Boring Mollusks. 



WE have seen from the last chapter that a stream of 

 lava continues intensely hot for a long time, and 

 may emit vapour, and even go on creeping slowly down the 

 mountain side for years after it has been poured forth. 



Long after it has ceased to move, and centuries after it 

 has become perfectly cold and solid, the surface of the 

 stream will remain fresh, smooth, and glossy, effectually re- 

 sisting all attempts both of air and weather to convert it 

 into dust, as we may see by the lava streams of Ascension 

 Island. 



Even lava has to yield at last, however, and that to 

 workmen whom we should at first sight be inclined to call 

 very insignificant, nothing more, indeed, to all appearance, 

 than mere stains, such as one sees upon a brick wall. 

 These discolour the surface here and there, and upon 

 examination with the microscope prove to be vegetables, of 

 a very humble kind it is true, but still vegetables, Nature's 

 gardeners and first soil-makers, which will prepare the way 

 for more important plants. Lichens, as they are called, are 

 to be found everywhere ; no climate, hot, cold, damp, or 



