MOUNTAIN PEDESTALS. 205 



A similar, though more obscure relation between the growth of moun- 

 tains and the upheaval of the non-folded districts about them is trace- 

 able in Europe, and apparently exists in all the continental fields. Thus, 

 as in America, we note that the mountains are bordered by relatively 

 high lying tablelands, and that the altitude of the whole field depends, 

 in large part at least, on the movements of underearth materials toward 

 the axes of disturbance by folding. 



The amount of this inner earth-matter which has moved toward the 

 mountain-built sections of the land cannot, in the present state of our 

 information, be well computed. It seems to me, however, that much of 

 the height of the continents, perhaps nearly the whole of the upliftings 

 which serves to retain its masses above the plane of the ocean, may be 

 attributed to this subterranean migration of rocks. If this view be cor- 

 rect, then we should regard the continents, at least so far as their history 

 as dry lands is concerned, as in great part the product of mountain- 

 building forces. In this work the primal action is the movement of rock 

 materials toward the axes of disruption and the consequent elevation of 

 the region where the movements occur. In a secondary, yet important, 

 manner the process of erosion removes a portion of the highlands, dis- 

 tributing the waste in a measure over the surface of the pedestals, thereby 

 increasing their elevation on the flanks of the range. There are thus two 

 contrasted movements of the materials involved in mountain-building — 

 in the interior, toward the centers of elevation, and on the surface, away 

 from those upland districts. 



Causes of Mountain- uplift Ing above Sealevel. — Although the process of 

 mountain-building may account for the growth of continental areas it 

 cannot be used to explain the process which brought the uplifted areas 

 of the earth above the ocean-level. As before noted, the evidence derived 

 from the distribution of these elevations leads us to the conclusion that 

 they do not develo]) in the depths of the seas. It appears to me, how- 

 ever, that from the recent extension of our knowledge concerning the 

 configuration of the sea-floors we may discern certain features there 

 which perhaps seem to account for the uplifting of the continental arches 

 to the water-level. At various points on the ocean-bottom we note the 

 existence of broad ridges which rise five, ten, or even fifteen thousand 

 feet above the deeps which lie about them. There is such a ridge in the 

 middle of the Atlantic, and another less distinct, perhaps because less well 

 known, in the southern division of that ocean. In various other districts 

 there are indications of similar broad uplifts, though the progress of our 

 knowledge concerning the topography of the sea-bottoms has not as yet 

 enabled us to trace their forms in a clear way. 



It seems to me a fair hypothesis that the formation of a great land-area 

 began by the elevation of one or more of these submarine ridges above 



