4 THE FLOOR OF THE OCEAN 



of each continent; about the reasons why Dead Sea, Caspian 

 Sea, and Death Valley of California are below sealevel, and 

 why mediterranean seas have replaced broad regions of dry 

 land. All these and many other facts may be grouped under a 

 single formula: the earth's body is plastic. 



Whence comes this plasticity? The accessible rocks are in 

 general brittle, not plastic. The relative weakness of the ter- 

 restrial materials must be, then, at depth; at what depth? To 

 answer this question we must have more and more informa- 

 tion about the structure of the earth's body in oceanic areas as 

 well as under the land surfaces. The major mysteries of land 

 geology itself are planetary, and to a large extent their secrets 

 lie hidden under the ocean. 



The learning of those secrets will mean a wide extension 

 of the field of knowledge and therewith a new call on human 

 courage. The tax on the will of man is growing as knowledge 

 grows. When the ascertained facts of Nature were compara- 

 tively few, even Aristotle had to add boldness to genius in 

 drawing a picture of the universe. Nearly two thousand years 

 later, men were still not disheartened by floods of new dis- 

 coveries, but wrote "natural philosophies," syntheses of known 

 facts, old and new. Since Newton's time the field of knowl- 

 edge has spread like an exploding rocket, and perforce science 

 has become compartmented. Yet this involves danger of pro- 

 found error, because Nature, reality, is not compartmented. 

 In final analysis, the "flower in the crannied wall" is the prob- 

 lem of the universe. This principle of mutual dependence 

 among the sciences is particularly clear to the geologist, whose 

 job is to deduce the structure and history of a whole planet, 

 with due regard to the steadily revised principles of a dozen 

 other sciences. And the geologist has found that in his own 

 field he must cover ground three times more extensive than 

 that where hammer, compass, and foot-work are his traditional 



