ALKALI SOILS 



43 



Wliat Becomes of the Materials Carried Into the Sea. — The 



sand settles out near the shore, and in time becomes sandstone 



(Fig. 17). 



The clay settles to the bottom farther out and finally turns 

 to shale. 



The saltfe remaining in solution become the "salt of the sea/' 

 Shells. — The carbonate of lime is taken out of solution in the 

 ocean water by myriads of tiny shell animals, whose shells sink to 

 the ocean floor when they die. Coral animals, certain water 

 plants and bacteria also cause carbonate of lime to be deposited. 

 Usually, however, on the sea bottom beyond the accumulations 



Fig 17 — The ocean receives all the materials washed from the continents The sand 

 settles out of the river waters near shore, and the clay is carried farther out The salts 

 make the sea-water salty The dissolved carbonate of lime is taken out of solution by 

 tiny shell animals. 



of sand and mud there are deposited shells and particles of carbon- 

 ate of Hme which in time turn into limestone. As a general rule, 

 whenever limestone, sandstone or shale is found, there at one 

 time existed a sea or lake. 



The mud and sand, which are the impurities of limestone, con- 

 stitute the soil-forming material when limestone weathers. 



Alkali Soils. — Soils in regions of little or no rainfall are not 

 leached as they are in humid ot sub-humid climates. The salts 

 formed through weathering processes, therefore, accumulate in 

 these soils. In places the soils are so salty that cultivated plants 

 cannot grow in them (Fig. 18). Such soils are called "alkali 

 soils." Salty crusts commonly form on their surfaces. When 



