436 THE GEOSPHERES 



First as to definitions — definitions rendered the more neces- 

 saiy for the reason that the essential ideas which I wish to ex- 

 press have not yet found their way into the dictionaries. Since 

 early in the history of knowledge, men have recognized the 

 atmosphere — i. e., the body of air above the earth. At first the 

 recognition was vague; it became more and more definite as 

 time went on ; and now educated men and women and children 

 know the atmosphere as a gaseous envelope surrounding the 

 solid earth, an envelope composed of a complex mixture of sub- 

 stances, chiefly of oxj-gen and nitrogen. This atmosphere is 

 one of the geospheres, the outermost of four. 



Since the beginning of knowledge, too, men have perceived 

 the waters of the earth ; and, as time has gone on, they have 

 recognized more and more clearly the substantial unity of the 

 standing waters of ocean and bay and lake, the running waters 

 of springs and rivers, and the solid waters of Arctic and Antarctic 

 snows and the glaciers of mountain and pole ; and they are com- 

 ing to extend the unity to include the aqueous vapor of the air, 

 one of the constituent gases of the atmosphere. Water is a defi- 

 nite mineral substance existing in three forms, as solid, liquid, 

 and gas, though chiefly in the second form ; it constitutes a 

 hydrosphere — the second of the four geospheres — covering the 

 greater part of the solid earth and covered by the greater part 

 of the atmosphere. 



Human knowledge began with the recognition of the solid 

 earth ; as time passed the knowledge became definite through 

 the endless interactions between human mind and human en- 

 vironment ; and today most intelligent people recognize a ter- 

 restrial sphere beginning with the soils and rocks beneath their 

 feet, passing beneath river and lake and ocean to the antipodes, 

 and extending from equator to pole in a spheroidal mass forming 

 the visible solid part of our planet. Now it is only the superfi- 

 cial portion of this spheroidal mass which lies within reach of 

 observation; this is the rocky crust of the earth, the object- 

 matter of the science of geology ; it consists of a wide variety of 

 mineral substances, mainly combined in rocks of a specific grav- 

 ity averaging about 2.70: This earth-crust forms the lands of 

 the earth and the basins of the oceans ; all of the geographic and 

 topographic features so well described by Dr Redway are built 

 up or carved out of it ; the continents, the islands, the valleys, 

 the mountains of the world represent this vast mass of rock- 



