654 Scientific Proceedings, Royal Dublin Society. 



In the case, therefore, of a continental island a thousand miles 

 across, and rising about 1320 feet above the sea-level, the effect 

 of the attraction on the oceanic waters will be to raise the imagi- 

 nary surface in the interior about 400 feet above a geodetically 

 determined level ; while the rise along the coast will be less. But 

 Professor Stokes very truly adds, the effect in the case of a great 

 continent might be considerably greater. Where, for instance, we 

 have a continent such as that of South America, from 2000 to 

 3000 miles across, rising from an ocean of an average depth of 

 15,000 feet, and bounded by the giant mountain range of the 

 Andes, with an average level of 12,000 to 16,000 feet, who can say 

 what the effect of the mutual attraction of this mass of land on the 

 surface of the Pacific Ocean may amount to ? Certainly consider- 

 ably more than in the hypothetical case of Professor Stokes. In 

 certain cases the effect of this rise, in altering the superficial 

 areas of land and sea would be very considerable ; but, owing 

 to the comparatively steep gradients of the coast and mountain 

 slopes, as well as of the submerged portions along the Pacific 

 borders, the effect in diminishing the area of submerged marginal 

 lands is less apparent than if the gradients were more gentle. 



The same observations apply, in a less degree, to North 

 America. 



The effect of such an arrangement of the configuration of ocean 

 a ad continent as is presented along the western sea-boards of the 

 American continents, where extensive mountain ranges and ele- 

 vated plateaus stretch for thousands of miles along the borders of 

 a deep ocean, must be much greater than is generally supposed. 

 The orographical characters of these continents, r and their relations 

 to the oceanic waters, may be regarded as affording the required 

 conditions for bringing about a maximum result in the elevation 

 of the ocean-surface. The most powerful attractive force is that 

 exercised by the lands immediately adjoining the sea-board ; and 

 as we recede from this line inland the attractive force necessarily 

 diminishes as the square of the distance. Hence the conditions 

 required for the maximum effect are found when there is an 

 accumulation of solid matter in the form of mountain ranges close 

 to the coast-line ; and this is exactly what happens in the case of 

 the American continents. Judging from the elevations and 

 breadth of the range of the Andes of Peru, and Bolivia, in South 



