THE EARTH AS A WHOLE 7 



meters ; * while the sea may be represented l)y a prismatic block 

 (tetragonal) having twice that volume (1,330.0-^-651.8—2.04). If, 

 then, we were to tiatten out all irregularities of the sea bottom by 

 cutting down the land block sufficiently to fill them, or, in other 

 words, if we distribute the land block of 651.8 million cubic kilo- 

 meters over the entire surface of the earth, 509,950,000 square 

 kilometers, according to IJessel, it would raise the mean level of 

 the ocean floor by the quotient of 65 1 .8 -f- 509.9 == i .278 kilo- 

 meters. The level of the earth's crust would therefore be 



— 3,681-1-1,278= — 2,403 meters, or approximately — 2,400 

 meters ( — 1,313 fathoms) below the present sea-level. This is 

 called the mean sphere level {uiittlerc Krnstenniveau), which Penck 

 originally placed at — 2,500 meters ( — 1,367 fathoms), but more 

 recently at 2,400 meters (22:7^5). Mill (19:75^), using the fig- 

 ures of Sir John Murray, for height of l?nd and depth of ocean 

 cited above, finds the mean sphere level to be — 2,560 meters or 



— 1,400 fathoms, while Romieux (24:99/) from the same data 

 finds it to be approximately — 2,360 meters ( — 1,290 fathoms). 

 For the whole earth, 222 million square kilometers lie above this 

 mean sphere level and 288 million square kilometers below it. \i 

 we assume a smooth lithosphere, the surface of which would cor- 

 respond to the mean sphere level, and the available sea water 

 (1,330 million cubic kilometers) were uniformly spread over this 

 surface, we would have an approximate but uniform depth of 2,600 

 meters (1,422 fathoms) for the universal ocean (1,330.0-^509.0= 

 2.608 kilometers). The oceanic areas below this depth of 2,400 

 meters (or approximately 1,300 fathoms) constitute the ahvsmal 

 areas; those above this to the edge of the continental shelf (200- 

 nieter or approximately loo-fathom line) the transitional areas 

 {die aktischen Regionen of Penck) and those above this level 

 ( — 200 meters to -1-8,840 meters) as the continental area 

 ( Penck ).t 



The Continental Block. The conception of a continental 

 block was introduced by H. Wagner (31 :/'4p) for the mass of land 

 (222 million square kilometers in basal area) which rises above 

 the mean crustal level. This he divides into: i. The continental 

 slope ( Kontinentalabhang ) , between the median sphere level and the 



* If we represent the continental mass as a prismatic block with a square 

 base of 148,800,000 square kilometers of area, a side of 12,198.36 kilometers, 

 and a height of 4,380 kilometers, on the scale of 1/1,000,000, we would have a 

 block of square base 12.2 meters on the side, and 4.38 mm. in height and nearly 

 one-fifth of this or 0.83 mm. would represent the part above sea-level. 



t In the original classification by Dr. Hugh Robert Mill, the line between the 

 transitional and the continental areas was drawn at sea-level. 



