TRANSACTIONS OF SECTION E. 809 



volcanic ridges, and by uplifts of Tertiary strata, which continue along the line of 

 the Nicobar and Andaman Islands into Burma. Thus the coast-lines of that section 

 of the Indian Ocean exhibit a geographical development similar to that of the Pacific 

 sea-board. Elsewhere, as in Hindustan, Arabia, and East Africa, the coast-lines 

 appear to have been determined chiefly by regional elevations of the land or sub- 

 sidence of the oceanic trough in Mesozoic and Oainozoic times, accompanied by the 

 outwelling of enornjous floods of lava. Seeing, then, that the Pacific and the 

 Indian Oceans are pre-eminently regions which, down to a recent date, have been 

 subject to great crustal movements and to excessive volcanic action, we may infer 

 that in the development of their coast-lines the sea has played a very subordinate 

 part. The shores, indeed, are largely protected from marine erosion by partially 

 emerged volcanic ridges and by coral islands and reefs, and to a considerable 

 extent also by the sediment which in tropical regions especiallj' is swept down to 

 the coast in great abundance by rains and rivers. Moreover, as the geological 

 structure of these regions assures us, the land would appear seldom to have 

 remained sufficiently long at one level to permit of much destruction by waves 

 and tidal currents. 



In fine, then, we arrive at the general conclusion that the coast-lines of the 

 globe are of verj' unequal age. Those of the Atlantic were determined as far bact 

 as Palgeozoic times bj' great mountain uplifts along the margin of the continental 

 plateau. Since the close of that period many crustal oscillations have taken 

 place, but no grand mountain-ranges have again been ridged up on the Atlantic 

 sea-board. Meanwhile the Palaeozoic mountain-chains, as we have seen, have 

 suffered extensive denudation, have been planed down to the sea-level, and even 

 submerged. Subsequently converted into land, wholly or partially as the case may 

 have been, they now present the appearance of plains and plateaus of erosion, often 

 deeply indented by the sea. No true mountains of elevation are met with any- 

 where in the coast-lands of the Atlantic, while volcanic action has well-nigh ceased. 

 In short, the Atlantic margins have reached a stage of comparative stability. The 

 trough itself, however, is traversed by at least two well-marked banks of upheaval 

 — the great meridional Dolphin Ridge, and the approximately transmeridional 

 Faeroe-Icelandic belt — both of them bearing volcanic islands. 



But while the coast-lands of the Atlantic proper attained relative stability at 

 an early period, those of the Mediterranean and Caribbean depressions have up to 

 recent times been the scenes of great crustal disturbance. Gigantic mountain- 

 chains were uplifted along their margins at so late a period as the Tertiary, and 

 their shores still witness volcanic activity, 



It is upon the margins and within the trough of the Pacific Ocean, however, 

 that subterranean action is now most remarkaljly developed. The coast-lines of 

 that great basin are everywhere formed of grand uplifts and volcanic ranges, which, 

 broadly speaking, are comparable in age to those of the Mediterranean and Carib- 

 bean depressions. Along the north-east margin of the Indian Ocean the coast-lines 

 resemble those of the Pacific, being of like recent age, and similarly marked by tlio 

 presence of numerous volcanoes. The northern and western shores, however (as 

 in Hindustan, Arabia, and East Africa), have been determined rather by regional 

 elevation or by subsidence of the ocean-floor than by axial uplifts, the chief 

 crustal disturbances dating back to an earlier period than those of the East Indian 

 Archipelago. It is in keeping with this greater age of the western and northern 

 coast-lands of the Indian Ocean that volcanic action is now less strongly manifested 

 in their vicinity. 



I have spoken of the comparative stability of the earth's crust within thi^ 

 Atlantic area as being evidenced by the greater age of its coastal ranges and the 

 declining importance of its volcanic phenomena. This relative stability is further 

 shown by the fact that the Atlantic sea-board is not much disturbed by earth- 

 quakes. This, of course, is what might have been expected, for earthquakes are 

 most characteristic of volcanic regions and of those ai'eas in which mountain-uplift.s 

 of recent geological age occur. Hence the coast-lands of the Pacific and the East 

 Indies, the borders of the Caribbean Sea, the volcanic ridges of the Atlantic basin, 

 the lauds of the Mediterranean, the Black Sea, and the Aralo-Caspian depressions, 



