PRELIMINARY OUTLINE. 



11 



of the ocean were removed, the outlines of the land would correspond 

 quite closely with the border of the true continental platform. 



It is customary to look upon the protrusions of the continents 

 as the great features of the earth's surface, but in reality the oceanic 

 depressions are the master phenomena. In breadth, depth, and capacity 

 they much exceed the continental protrusions, and if the earth be 

 regarded as a shrunken body, the settling of the ocean bottoms has 

 doubtless constituted its greatest surface movement. From the esti- 

 mates of Murray, Gilbert has derived the following tables, showing 

 the relative areas of the lithosphere above, below, and between certain 

 levels.* 



From these estimates it appears that if the surface were graded to 

 a common level by cutting away the continental platforms and dump- 

 ing the matter in the abysmal basins, the average plane would lie 

 somewhere near 9000 feet below the sea-level. The continental plat- 

 form may be conceived as rising from this common plane rather than 

 from the sea-level. 



Contours. 



Percent, of Surface 

 above. 



Percent, of Surface 

 below. 



Contour 24,000 feet above sea-level ... 



0.004 



0.09 



0.7 



2.3 

 27.7 

 42.5 

 57.3 

 96.8 

 99.93 



99 996 



" 18,000 " '' " 



99 91 



" 12,000 " '' '' 



99 3 



" 6,000 " " '' 



97 7 



Sea-level 



72 3 



Contour 6,000 feet below sea-level 



57 5 



12,000 " '' '' 



42 7 



" 18,000 " '' '' 



3 2 



" 24,000 '<<''' ... 



07 







Percent. 



More than 6000 feet above sea-level 2.3 



Between sea-level and 6000 feet above 25 . 5 



Between sea-level and 6000 feet below 14.8 



Between 6000 and 12,000 feet below sea-level 14.8 



Between 12,000 and 18,000 feet below sea-level 39.4 



Between 18,000 feet and 24,000 feet 3.1 



Epicontinental seas. — Those shallow portions of the sea which lie 

 upon the continental shelf, and those portions which extend into the 

 interior of the continent with like shallow depths, such as the Baltic 



* The Earth. Johnson's Encyelop^edia. See also statement of Murray in Smith- 

 sonian An. Rept., 1899, p. 312. Reprint from Brit. A. A. S., Dover meeting, 1899, and 

 Scot. Geog. Mag., Vol. XV, 1899, p. 511. 



