LAND AND WATER. 603 



embouchure, or to lie beneath the surface and form rock once more. The 

 igneous rocks, composed of lavas and ashes, are volcanic rocks, deposited 

 deep down, and then after the lapse of ages disclosed by the action of air 

 and water. 



The consideration of the land and water upon the globe shows us that 

 they are distributed over the earth very unequally. There is nearly three 

 times as much water in our planet as there is land, and these proportions 

 could not be altered without giving rise to phenomena, the results of which 

 cannot be properly estimated. Our earth has an area of 197,000,000 of 

 square miles; about 52,000,000 of this is land, and about 145,000,000 of 

 it water; so about three-quarters of the globe is made up of water. The 

 first portion of our subject therefore should be directed to the examination 



Fig. 690. Distribution of land and water. 



and consideration of water, and the phenomena which arise from its presence 

 upon the earth. 



We need not go into details which every geography indicates. We will 

 try to trace the sources, not the plain effects, which all can afterwards study 

 from special books. In a preceding portion of this volume we have explained 

 the chemical composition of water, and we showed by experiment that it is 

 a fluid composed of oxygen and hydrogen gases, in the proportions of one 

 to two volumes respectively. No matter in what form water may appear, 

 as water, as ice, or as steam, these proportions never vary in pure water 

 (see p. 352). But water on the earth is seldom, or never, pure. We know 

 the difficulty we have to procure good drinking water, and though it may 

 be filtered, there will remain natural salts, which are found in different 

 degrees in all water upon the globe. We know the rain, which is perfectly 



