Changes in Distribution of Land and IVater. 1 2 7 



3000 fathoms, the distance from the shore at which they are 

 found is seldom less than forty or sixty miles— that is to say, a 

 descent of one mile in twenty miles, or an angle of about 3° 

 (Fig. 14). On measuring the inclines of several islands of 

 volcanic origin, such as Pico in the Azores, Ascension Island 

 Marion Island, and the island of Hawaii, as these appear on 

 sketches made during the cruise of H.M.S. " Challenger," the 

 angle is found to decrease from an average of 30° at the crater 

 or craters, to 15° and 10° upon the intermediate slopes, while the 

 final incline dips into the sea at an angle of from 10° to 6° — that 

 is to say, a fall of one mile in ten miles, which a few miles from 

 the shore is reduced to 3°, or a fall of one mile in twenty miles. 

 Yet those islands have the aspect of rising abruptly from the 

 level of the sea, and depths of over 2000 fathoms are obtained 

 within a few hours' sail from their shores. 



The purpose of the above remarks is to point out that 

 continents are but the most elevated areas of wide and low 

 undulations, and that these differ in no respect from the sub- 

 marine plateaux discovered by recent exploring expeditions, 

 except in having partially risen above the surface of the ocean. 

 We also see that, on account of the low angle of the inclines, 

 a comparatively slight alteration either in the level of the 

 land or in the level of the sea may produce a considerable 

 change in the distribution of land and water, and that the 

 rise and fall of these undulations rarely exceed five miles in 

 a distance of 100 miles, and are generally much below this 

 proportion. 



The comparatively rapid increase of depth beyond the 100- 

 fathom line was a phenomenon of sufficiently frequent occurrence 

 to attract the attention of those engaged in the recent sounding 

 operations, and can hardly be considered as accidental. It has 

 probably some connection with the limits of the alterations of 

 level which have taken place during the most recent geological 



