354 



NATURE 



[August i i, 1892 



deposits, were converted into high lands. During this stage not 

 much rock-folding took place, nor were any true mountains of 

 elevation formed parallel to the Atlantic margins. It was other- 

 wise, however, in the Mediterranean and Caribbean depressions, 

 where coastal movements resulted in the formation of enormous 

 linear uplifts. Moreover, volcanic action is now and has for 

 a long time been more characteristic of these depressions than 

 of the Atlantic coast-lands. 



I must now ask you to take a comprehensive glance at the 

 coast-lines of the Pacific Ocean. In some important respects 

 these offer a striking contrast to those we have been considering. 

 Time will not allow me to enter into detailed description, and I 

 must therefore confine attention to certain salient features. 

 Examining first the shores of the Americas, we find that there 

 are two well-marked regions of fiords and fringing islands — 

 namely, the coasts of Alaska and British Columbia, and of 

 South America from 40° S.L. to Cape Horn. Although these 

 regions may be now extending seawards in places, it is obvious 

 that they have recently been subject to submergence. When 

 the fiords of Alaska and British Columbia existed as land 

 valleys it is probable that a broad land connection obtained 

 between North America and Asia. The whole Pacific coast is 

 margined by mountain ranges, which in elevation and boldness 

 far exceed those of the Atlantic sea- board. The rocks entering 

 into their formation range in age from Archaean and Palaeozoic, 

 and they are almost everywhere highly disturbed and flexed. 

 It is not necessary, even if it were possible, to consider the 

 geological history of all those uplifted masses. It is enough for my 

 purpose to note the fact that the coastal ranges of North America 

 and the principal chain of the Andes were all elevated in Tertiary 

 times. It may be remarked further, that from the Mesozoic 

 period down to the present the Pacific borders of America have 

 been the scene of volcanic activity far in excess of what has been 

 experienced on the Atlantic sea-board. 



Geographically the Asiatic coasts of the Pacific offer a strong 

 contrast to those of the American borders. The latter, as we have 

 seen, are for the most part not far removed from the edge of the 

 continental plateau. The coasts of the mainland of Asia, on the 

 other hand, retire to a great distance, the true margin of the 

 plateau being marked out by that great chain of islands which 

 extends from Kamchatka south to the Philippines and New 

 Guinea. The seas lying between those islands and the mainland 

 occupy depressions in the continental plateau. Were that pla- 

 teau to be lifted up for 6,000 or 7,000 feet the seas referred to 

 would be enclosed by continuous land, and all the principal 

 islands of the Indian Archipelago — Sumatra, Java, Celebes, and 

 New Guinea, would become united to themselves as well as to 

 Australia and New Zealand. In short, it is the relatively depressed 

 condition of the continental plateau along the western borders of 

 the Pacific basin that caused the Asiatic coast-lines to differ so 

 strikingly from those of America. 



From a geological point of view the differences are less striking 

 than the resemblances. It is true that we have as yet a very 

 imperfect knowledge of the geological structure of Eastern Asia, 

 but we know enough to justify the conclusion that in its main 

 features that region does not differ essentially from Western 

 North America. During Mesozoic and Cainozoic times the sea 

 appears to have overflowed vast tracts of Manchooria and China, 

 and even to have penetrated into what is now the great Desert 

 of Gobi. Subsequent crustal movements revolutionised the 

 geography of all those regions. Great ranges of linear uplifts 

 came into existence, and in these the younger formations, to- 

 gether with the foundations on which they rested, were 

 squeezed into folds and ridged up against the nuclei of 

 Palaeozoic and Archaean rocks which had hitherto formed the 

 only dry land. The latest of these grand upheavals are of 

 Tertiary age, and, like those of the Pacific slope of America, 

 they were accompanied by excessive volcanic action. The long 

 chains of islands that flank the shores of Asia we must look upon 

 as a series of partially submerged or partially emerged mountain- 

 ranges, analogous geographically to the coast ranges of North 

 and Central America, and to the youngest Cordilleras of South 

 America. The presence of numerous active and recently extinct 

 volcanoes, taken in connection with the occurrence of many 

 great depressions which furrow the floor of the sea in the East 

 Indian Archipelago, and the profound depths attained by the 

 Pacific trough along the borders of Japan and the Kurile and 

 Aleutian Islands — all indicate conditions of very considerable 

 instability of the lithosphere. We are not surprised, therefore, 

 to meet with much apparently conflicting evidence of elevation 



and depression in the coast-lands of Eastern Asia, where in 

 some places the sea would seem to be encroaching, while in 

 other regions it is retreating. In all earthquake-ridden and 

 volcanic areas such irregular coastal changes may be looked for. 

 So extreme are the irregularities of the sea-floor in the area 

 lying between Australia, the Solomon Islands, the New 

 Hebrides, and New Zealand, and so great are the depths 

 attained by many of the depressions, that the margins of the 

 continental plateau are harder to trace here than anywhere else 

 in the world. The bottom of the oceanic trough throughout a 

 portion of the Southern and Western Pacific is, in fact, traversed 

 by many great mountain rides, the summits of which approach 

 the surface again and again to form the numerous islets of 

 Polynesia. But notwithstanding the considerable depths that 

 separate Australia and New Zealand there is geological evidence 

 to show that a land connection formerly linked both to Asia. 

 The continental plateau, therefore, must be held to include New 

 Caledonia and New Zealand. Hence the volcanic islets of the 

 Solomon and New Hebrides groups are related to Australia in 

 the same way as the Riu-kiu, Japanese, and Kurile Islands are to 

 Asia. 



Having rapidly sketched the more prominent features of the 

 Pacific coast-lines, we are in a position to realise the remark- 

 able contrast they present to the coast-lines of the Atlantic. 

 The highly folded strata of the Atlantic sea-board are the relics 

 of great mountains of upheaval, the origin of which cannot be 

 assigned to a more recent date than Palaeozoic times. During 

 subsequent crustal movements no mountains of corrugated strata 

 were uplifted along the Atlantic margins, the Mesozoic and 

 Cainozoic strata of the coastal regions showing little or no dis- 

 turbance. It is quite in keeping with all this that volcanic 

 action appears to have been most strongly manifested in 

 Palaeozoic times. So many long ages have passed since the 

 upheaval of the Archaean and Palaeozoic mountains of the 

 Atlantic sea-board that these heights have everywhere lost the 

 character of true mountains of elevation. Planed down to low 

 levels, partially submerged and covered to some extent by 

 newer formations, they have in many places been again con- 

 verted into dry lands, forming plateaus— now sorely denuded 

 and cut up into mountains and valleys of erosion. Why the 

 later movements along the borders of the Atlantic basin 

 should not have resulted in the wholesale plication of the 

 younger sedimentary rocks is a question for geologists. It 

 would seem as if the Atlantic margins had reached a stage of 

 comparative stability long before the grand Tertiary uplifts of 

 the Pacific borders had taken place ; for, as we have seen, the 

 Mesozoic and Cainozoic strata of the Atlantic coast-lands show 

 little or no trace of having been subjected to tangential 

 thrusting and crushing. Hence one cannot help suspecting 

 that the retreat of the sea during Mesozoic and Cainozoic ages 

 may have been due rather to subsidence of the oceanic trough 

 and to sedimentation within the continental area than to positive 

 elevation of the land. 



Over the Pacific trough, likewise, depression has probably 

 been in progress more or less continuously since Palaeozoic 

 times, and this movement alone must have tended to with- 

 draw the sea from the surface of the continental plateau in 

 Asia and America. But by far the most important coastal changes 

 in those regions have been brought about by the crunipling 

 up of the plateau, and the formation of gigantic mountains of 

 upheaval along its margins. From remotest geological periods 

 down almost to the present the land area has been increased 

 from time to time by the doubling-up and consequent eleva- 

 tion of coastal accumulations and by the eruption of vast masses of 

 volcanic materials. It is this long-continued activity of 

 the plutonic forces within the Pacific area which has caused, 

 the coast-lands of that basin to contrast so strongly with those 

 of the Atlantic. The latter are incomparably older than the 

 former — the heights of the Atlantic borders being mountains of 

 denudation of vast geological antiquity, while the coastal ranges 

 of the Pacific slope are creations but of yesterday as it were. 

 It may well be that those Cordilleras and mountain-chains reach 

 a greater height than was ever attained by any Palaeozoic uplifts 

 of the Atlantic borders. But the marked disparity in elevation 

 between the coast-lands of the Pacific and the Atlantic is due 

 chiefly to a profound difference in age. Had the Pacific coast- 

 lands'existed for as long a period and suffered as much erosion 

 as the ancient rocks of the Atlantic sea-board, they would now 

 have little elevation to boast of. 



The coast-lines of the Indian Ocean are not, upon the whole,. 



NO- II 89, VOL. 46] 



