32 ON THE GENERAL DISPOSITION OF THE 



remarkable feature, namely, the inequality of its ele- 

 vations, be considered, it is plain that these are merely 

 convertible propositions. With the forms of conti- 

 nents or the distribution of islands, geology can there- 

 fore have no concern, otherwise than as these are 

 necessary consequences of differences of elevation, and 

 are dependent on Geological causes. 



Those who have treated of physical geography, 

 have attempted many generalizations on this subject; 

 but these seem to establish no principles, and they 

 add nothing to that knowledge which may be derived 

 with much more ease from the inspection of a terres- 

 trial globe. If we examine what has been written on 

 the directions of Capes and coasts, or the correspon- 

 dences of bays and head-lands, we shall find nothing 

 which can be referred to any general law. Whatever 

 modifications exist, they are particular cases; and, 

 wherever they occur, they depend on the altitudes and 

 directions of elevated land, or on the positions of the 

 mouths of rivers ; circumstances which, as far as they 

 are subject to any rules, will be examined hereafter. 



The greatest elevation of land has been measured; 

 but its greatest depression, being concealed by the. 

 sea, is beyond the reach of our instruments. Thus we 

 are still ignorant of the quantity by which the least 

 extreme diameters of the solid earth differ from the 

 mean mathematical ones. 



But by La Place's computation, founded on the 

 theory of the tides, the mean depth of the sea must 

 be four leagues. If we admit that to be only its ex- 

 treme depth, and that the height of the Hi malya ridge 

 is 5 miles, we shall have a minimum diameter differing 

 from the greatest by ~- Q part, nearly, of the mean. 

 But whatever the maximum differences of such in- 

 equalities are now. it is certain that they have once 



