ig2r. No. II. THE STRAXDFLAT AND ISOSTASV. 235 



Ocean being a])out 36 i.i millions square kilometres, and the area of the 

 land surface of the earth being- about 148.8 millions sq. km., we have: 



// -36 1. 1 = // 148.8 

 // = 2.43 II. 

 To give room for a universal depression of the Ocean floor the 

 continents have consequently to be elevated on the average 2.4 times the 

 average amount of this depression. This reduces substantially the depth 

 to wliich the Ocean floor can be depressed by a certain additional weight. 

 If perfect equilibrium be established, the pressure at a certain level below 

 the earth's surface should be uniform in all regions. Hence the increase 

 of pressure at this level created !)y the increase of the depth of the Ocean 

 must be equal to the increase of pressure caused by the upheaval of the 

 continents. Hence 



dxi — WX3 = h>^2> = 2.43 >'//>' 3 



II ^= ^ a ■ o.og-] 



3 - 2.43 3 



where d is the increase of the depth of the Ocean. If this increase be 

 100 metres, we find that the depression of the Ocean floor thereby caused 

 can be no more than 9.7 metres, while the average upheaval of the con- 

 tinents would be 23.6 metres. 



To simplify our computation we have here assumed that the volume 

 of the Ocean was increased by water coming from outside the globe. In 

 reality the water is removed from the continents to the Ocean, which 

 complicates the matter. This removal causes an upheaval of the land in 

 the region of the ice-caps, and a sinking of the crust in the surrounding 

 regions, which will gradually extend over wider areas, but will only reach 

 a certain part of the Ocean floor. 



In this manner the universal upheaval of the continents caused by 

 the shift of the water from the ice-caps to the Ocean will be reduced, 

 and the possible depression of the Ocean floor may be increased 

 accordingly. 



On the other hand it would take an extremely long time before the 

 depression of the Ocean floor could effect a universal and equal upheaval 

 of the whole area of the continents. It would begin by pressing up th.e 

 coasts surrounding the Ocean, and the upheaval would only very slowly 

 extend landwards over the continents. Thus the depression of the sea- 

 floor would also be much checked. 



The whole process is thus seen to be a very complicated one, and 

 as so many important factors are unknown, it would be useless to try 

 to form any accurate estimate of the depression of the Ocean floor and 

 of the upheaval of the continental coasts. 



\\'e have here considered the case where there was an addition of 

 water to the sea l\v the melting of the ice-caps on land. In the opposite 



