100 ' ECONOMICAL GEOLOGY. 



perceived. They are remarkable, also, for their large per- 

 centage of ash, containing, when dried, about twice as 

 much as the dry land-grasses. The components of the 

 ash, too, are those most generally found in vegetable ashes. 

 The following is the average of analyses of the ash of 

 several species of sea-weeds, taken from " Morton's Cyclo- 

 pedia of Agriculture." 



Analysis of {he Ash of Sea-weed. 



Potash 17.50 



Soda 12.70 



Lime 7.39 



Magnesia 9.89 



Chloride of sodium 16.56 



Chloride of potassium 0.93 



Iodide of sodium 0.95 



Phosphate of lime 7.24 



Oxide of iron 0.24 



Sulphuric acid 24.76 



Silica 1.82 



99.98 

 Percentage of ash in weed dried at 212° Fah. 16.46 



Common sea-weed contains from seventy-five to eighty- 

 five per cent, of water j it is also said to contain, when dry, 

 two per cent, of nitrogen. When exposed to the air it 

 loses about half its water; the remainder, amounting to 

 not far from forty per cent., is retained with great perti- 

 nacity. " The organic, or combustible portion, principally 

 consists of a peculiar mucilaginous substance and of nitro- 

 genized compounds, which latter are the cause of the rapid 

 decay to which sea-weed is subject. 



" Sea-weed is more valuable as a green manure than any 



