"KELP." 159 



Many seaweeds grow with great rapidity, and rocks 

 which have been not only cleared but chiselled smooth, are 

 found covered in less than six months with a dense growth 

 of weed from two to six feet long, which must have sprung 

 from seed. Besides silica and lime, they take up other 

 minerals. Some take large quantities of magnesia ; iodine, 

 in combination with sodium and magnesium, is obtained 

 from the ash of certain species, and some of the olive- 

 coloured fuci contain so much sulphuric acid that where 

 they are thrown up in large heaps and left to decompose, as 

 is the case at Copenhagen, the silver in the neighbouring 

 houses quickly turns black. Most sea-weed ash contains 

 more or less soda, and that of the bladder fucus and some 

 other olive seaweeds, yields so much that in former times 

 many people made their living by it. The weeds were 

 burnt in pits, and the dark-brown, half glassy-looking cakes 

 of ashes, called "kelp," were sold for glass- and soap-making, 

 bleaching, and other purposes. Scotland and her islands 

 at one time supplied 20,000 tons of kelp annually ; but the 

 kelp-burners do little now, as the carbonate of soda, or soda 

 ash, is now manufactured in enormous quantities directly 

 from sea-salt. How does the salt, which sea-water contains 

 in such abundance, get into the sea ? Like the other 

 minerals, it is brought by the rivers ; but this some people 

 find it difficult to believe, since river-water is fresh, not 

 salt, and they prefer therefore to adopt the old notion that 

 there are vast beds of salt somewhere in the ocean. These 

 beds have not been discovered, however, and are therefore, 

 at present at all events, wholly imaginary, whereas it is no 

 imagination, but an ascertained fact, that all spring water, 



