6 WILLCOX : 



portion of the surface of the earth is covered with beds of 

 limestone rocks. Nearly all running waters contain carbonate 

 of lime in solution, and vast quantities of the latter are carried 

 daily into the sea. Much of this is, in turn, reconverted into 

 solid matter by the action of corals and shellfish. The pearl 

 consists of carbonate of lime. Limestone performs a most 

 important function as a flux in the smelting of iron and other 

 ores, and in making mortar and cement. 



The stalactites and stalagmites found in caves are formed 

 from waters containing carbonate of lime in solution. Rain 

 water, when slowly percolating through the fissures in the 

 limestone overlying caves, dissolves a small amount of the 

 rock. When it reaches the roof of the cave some of the water 

 is evaporated and the limestone that it contained is deposited 

 there. This process, when long continued, forms stalactites. 

 If the water flows slowly and all of it is dried on the ceiling, 

 only stalactites will be formed. But if some of such water 

 should fall to the floor a stalagmite will be formed there and 

 piled up slowly by the same process. In some cases stalac- 

 tites will continue to be formed downward and stalagmites to 

 grow upward until they reach each other and become united. 

 The pillars in caves are thus formed. 



The elements sodium and potassium have such an affinity 

 for oxygen that when in contact with water they immedi- 

 ately decompose it and combine with the oxygen furiously, 

 with the accompaniment of a great amount of heat. The 

 combination of sodium with oxygen forms soda, and potas- 

 sium combined with oxygen forms potash. Soda is abund- 

 antly found as a component of many mineral species. Ihiited 

 with chlorine it forms the salt of the oceans and of the salt 

 lakes. During the slow decomposition of the rocks of the 

 earth many of the substances composing the minerals are 

 made soluble and are leached out ami carried, in solulion, to 

 the salt lakes and into the oceans. 



The waters in the oceans are considered to have been ori- 

 ginally fresh, and sul)se(|uentl\- made saline 1)\- the salts car- 



