6 



PRINCIPLES OF STRATIGRAPHY 



have been reached by de Lapparent, Ileiderich and Murray, as 

 shown in the following table (Penck-21, i :/5o) : 



Percentage of 

 land surface 



Below 

 o m. 



From 

 o- 

 200 

 m. 



From 

 200- 



500 



m. 



From 



500- 



1,000 



m. 



From 



1,000- 



2,000 



m. 



From 



2,000- 



3,000 



m. 



Above 



3,000 



m. 



de Lapparent . 

 Heiderich .... 

 Murray 



0.08 

 0.00 



18.00 

 13 40 

 14.60 



20.00 

 37 96 

 38.00 



47.0 



28.5 

 25.8 



14.00 

 17.81 

 19.80 



1-95 I 0.30 

 I . 40 o . 40 



The mean elevation for all continents is given by Sir John Mur- 

 ray as 2,250 feet (686 meters), and the mean or average depth 

 of the ocean as 3,840 meters (2,100 fathoms). Penck (21:757; 

 22:77), on the other hand, finds the mean elevation of the conti- 

 nents and islands to be 735 meters and the mean depth of the 

 ocean 3,650 meters. The mean depth of the ocean has more re- 

 cently been calculated as 3,680 meters (precisely 3,681 meters) by 

 Kriimmel (iy.144), who also assumes the mean altitude of the 

 land at approximately 700 meters. More recently still Penck has 

 given these figures as 3,680 meters and 710 meters, respectively 

 (22:7<?5). With a land area of 148.8 million square kilometers, the 

 volume of the land mass above sea-level becomes 104.2 million 

 cubic kilometers. From these figures the following ratios are de- 

 duced : mean height of land to mean depth of sea = 700: 3,680 ^ 

 1:5.25; area of land to sea=i48.8 :36i.2r--i :2.43 : volume of 

 land to sea= 104.2 :i, 330.0= I :i 2.8. Thus (Kriimmel-17, i-i47) 

 it would take nearly 13 times the volume of the land rising above 

 sea-level to fill the sea, three times that volume to fill the Atlantic 

 Ocean, 2^4 times that volume to fill the Indian Ocean, and 63/2 

 times to fill the Pacific Ocean. 



The Mean Sphere Lev- el. If we regard the land mass as a 

 whole, we may represent it by a prismatic block (tetragonal) com- 

 posed of that portion which lies above mean ocean depth, plus that 

 portion rising above sea-level, giving a height of 3,6804-700= 

 4,380 meters, a base of 148.8 million square kilometers, the present 

 area of the land surface, and a volume of 651.8 million cubic kilo- 



