THE ANIMAL KINGDOM. 79 



These animals incessantly assail the framework of our 

 strongest ships, and by perforating their timbers place them 

 in danger and threaten them with instant shipwreck. It is 



30. Teredo, or Ship- Worm, and Fragment of Wood devoured by others. 



solely to preserve vessels from these terrible wood-devourers 

 that all vessels going on long voyages are copper-bottomed. 

 These, then, are the fragile molluscs which ravage our 

 naval structures ; later on we shall speak of the insects which 

 pitilessly consume our dwellings. 



CHAPTER IV. 



MOUNTAIN BUILDERS. 



TORN from the depths of the crust of the earth, and for- 

 cibly upheaved above the clouds by a formidable power, the 

 lofty mountain systems of the globe, such as the Alps and 



