394 POPULAR SCIENCE MONTHLY. 



clipping under the sea, it passes through Europe, and finally furnishes 

 the marble quarries of Greece. Heat, water, and chemical action 

 give a ceaseless variety to the forms of the limestone, but wherever 

 found it shows the former seat of an ocean. 



As soon as the " ooze " was lifted from below the sea it began 

 to change. Some has been exposed to heat and has crystallized into 

 marble, but for our purposes the most interesting changes have been 

 wrought by water. Chalk, limestone, and marble — for these are 

 chemically the same — are almost insoluble in pure water. But water 

 is rarely pure; it dissolves many things, and among them the car- 

 bonic-oxide gas that every fire, every animal, every decaying scrap 

 of wood is pouring into the atmosphere. The rain, charged with this 

 gas, dissolves the limestone, but when the gas escapes the lime falls, 

 as you know happens when " hard " water is boiled, for the heat 

 drives off the gas. By this solution, however, the lime is scattered 

 widely through the soil, and is rarely lacking in unfilled earth. 



Besides lime, phosphorus is necessary in a good soil. This is 

 widely spread in Nature, but its great reservoir is the ocean, that 

 boundless mine of wealth. Many marine animals have the power of 

 building it into their tissues, and the shells of oysters and other 

 mollusks, the bones of nearly all animals, terrestrial and marine, and 

 parts of other organisms, are composed of phosphates to a greater or 

 less degree. In the ceaseless changes of level the primal oyster beds 

 and coral reefs are raised to the surface or far above it, and the slow 

 action of time begins to tear down the deposits and spread them wide- 

 cast. Since that far-off time " in the beginning " no new matter has 

 been put on earth save the small amounts of the meteorites, and the 

 economy of Nature can allow not one atom to lie in idleness, but calls 

 on each one to play its part ceaselessly, " without haste and without 

 rest." A certain amount of a substance is disseminated through the 

 earth; by rains it is washed into the streams, and thence to the sea. 

 Here plants or animals eagerly await it, and by means of them it is 

 again restored to the land, to begin again its endless round. 



The metals most necessary for plant life are potassium, sodium, 

 and iron; indeed, the very name of the first shows its importance. 

 If the ashes which contain all the mineral constituents of plants be 

 put in a vessel and water poured on them, a solution of lye will per- 

 colate through the mass. The word lye is an abbreviation for alkali, 

 and when chemistry became sufficiently advanced, a metal was dis- 

 covered in this lye to which the name potassium — i. e., potash-metal 

 — was given. If seaweeds be burned and leeched in the same way 

 we can obtain from the lye another metal, sodium, that is much like 

 potassium, and that is one of the most widely spread substances on 

 earth as its chloride, or common salt. 



