on the Earth's Axis of Rotation. 447 



which on a sealess and rainless globe are equivalent, as far as 

 producing excesses or deficiencies of surface matter, to those 

 which obtain on the earth are referred to as " effective ;" and it 

 is only the effective elevation or subsidence which we require 

 to know in order to determine the shift of the earth's axis. 



The evidence as to area is very meager, because precise 

 boundaries to regions of elevation and subsidence cannot be 

 ■wigiied; but, faute de mieux, the author's father, Mr. Charles 

 Darwin, marked out for him on a map an area in the Pacific 

 Ocean which (on account of the structure of the coral islands) 

 he believes to have undergone subsidence within a recent 

 geological period. From a consideration of this and of other 

 points the author believes that from T ' s to j', of the whole 

 earth's surface may, from time to time, have undergone eleva- 

 tion and subsidence. The greatest vertical effective amount of 

 rise or fall cannot be determined from geological evidence, 

 because of the effects of erosion and of the influx of the sea into 

 parts below the mean level of the earth. 



The only way of determining the point seems to be to find 

 what is the difference of mass, standing on unit area of the 

 earth's surface, in an ocean of, say, 15,000 feet deep, and in 

 land of, say, 1100 feet high. From this difference of mass the 

 effective elevation of an ocean-bed in its conversion into land 

 ean be at once determined. Taking the above numbers, it is 

 found to be 10,436 feet; and in the examples given in the 

 following part, the deflection of the polar axis, for an assumed 

 effective elevation of 10,000 feet, is given in each case. 



It is then pointed out that, if the deformation of the earth 

 were of very wide extent, the level surface of the sea would 

 approximately follow the rocky surface, and that thus there 

 might be sufficient change in the earth's shape to sensibly affect 

 the position of the principal axis, without there being any 

 geological signs of elevation or subsidence. 



5. Numerical application is now made of the preceding work 

 to the case of the earth, and, as befctf stated, all the results are 

 given for 10,000 feet of effective elevation. 



The first application is to continents and seas of maximum 

 effect, and a table of results is given. "It may be here stated 

 that if ¥ | ¥ of the earth's surface is elevated, the deflection of 

 the pole is 11^'; if ^, 1° 46£' ; if T 'o> 3° 17'; and if 1, 8° 4i'.* 

 In each case ipposed to fall simultaneously. 



Other examples are then given for continents and seas which 

 do not satisfy the maximum condition ; in some the. boundaries 

 are abrupt cliffs, in others shelving. . 



The conei •. that a single large geological 



