GEOLOGICAL SUCCESSION OF CONTINENTS. 355 



Mountains, with the Alleghanies and Cordilleras of Brazil, may be 

 taken as skeleton contours, which are correlative with and dependent 

 upon the formation of the axis of the Eurasian continent ; while 

 the north to south mountains of the east and west sides of Southern 

 Africa, of Madagascar and Australia, show that a wide extension of 

 land from west to east about the northern parts of the world cannot 

 be upheaved without the development of correlative elevation in an 

 opposite direction, so as to use up a corresponding portion of the 

 earth's crust on the opposite side of the earth in the direction of 

 tension, which initiates contraction at right angles to itself. Hence, 

 the east to west direction of the Great Antilles is dependent upon 

 the north to south direction of the Andes. The deflection of Cen- 

 tral America north-west is governed by the direction of the Appal- 

 lachian chain north-east. The Suliman mountains and Ghats have a 

 like dependence upon the Himalayas. The existence of the oceans we 

 take to follow the same law as inland seas or other basins, and to be 

 dependent on the contractions which have upheaved the continents. 



We have entered into this statement concerning mountains 

 because the views enunciated seem to show an indication of law in 

 the distribution of land and water at the present day. Hence it may 

 be inferred, perhaps, that such a law has never been absent from the 

 earth ; and that in its natural development we find an interpretation 

 -of the great geological mystery of upheavals and depressions, which 

 caused the same region of the earth in past ages to have been 

 occupied successively by ocean and by land. It harmonises the 

 evolution of mountains by the radiation of the earth's heat, under 

 the principle that pressure of contraction must give rise to tension at 

 right angles to the contraction ; and that all chains are hence approxi- 

 mately at right angles to each other, and therefore succeed each other 

 in this order, both in space and in time. 



A mountain chain once formed can never be obliterated or 

 ignored by a newer chain crossing the same district ; and the rocks of 

 the folded region, no matter how denuded or depressed, will always 

 exhibit the conditions of their origin. In such a sense mountains 

 and continents may be said to be permanent ; but just as the forma- 

 tion of the great east to west ridges of the mountain axis of the Old 

 World drew the land up above the ocean to the north and south, in 

 Tertiary times, so we may anticipate that the line of contraction 

 which is outlined in the Dolphin and Challenger ridges would 

 by further elevation gradually draw the lands on both sides of the 

 Atlantic beneath the sea, and vary the geography of the world much 

 as it has changed in bygone times. In successive ages the great con- 

 tractions of the earth's crust are repeated, and upheaval and depression 

 take place in later ages along old lines of contraction ; but contraction 

 in one direction may be succeeded in the next period of geological 

 time by a contraction which is approximately at right angles, result- 

 ing in grand unconformity of the newer strata, because the origin of 

 rock material is different. 



