112 ROCK-METAMORPHISM. 



constituting the Alps and the Himalayas. Both mountain- 

 masses have been more or less affected by forces exerted in direc- 

 tions corresponding with the two principal sections of meridional 

 jointing; but in both cases the phenomenon has been greatly 

 swayed by movements presumably acting under the influence of 

 the equatorial system. 



The disturbances which developed High Asia a vast conti- 

 nental mass within a continent stretching from India to the 

 tundras of the Taimyr peninsula in Asiatic Siberia have 

 ridged it up transversely into mountain- chains, with intervening 

 desert platforms. Its southern extremity is formed by the Hi- 

 malayan and other ridges, whose general level (20,000 feet or 

 more in altitude) culminates in still loftier peaks, some not far 

 short of 30,000 feet. All the transverse ridges, in a great (or the 

 middle) portion of their length, have an east-and-west course. 



The development of High Asia is a vastly complex phe- 

 nomenon, presumably resulting from disturbances which have 

 been directed along different zones of weakness. The zone in 

 correlation with equatorial jointing seems to have been the 

 medium through which the transverse ridges and their respective 

 igneous axis were upheaved ; while those referable to the two 

 principal sections of meridional jointing may have similarly 

 influenced the terminations of the ridges on both sides of this 

 huge plateau, especially in the region east of it, where 

 mountain-ranges, coast-lines, and off-lying islands all coincide 

 in their strike with the east-of-north meridional jointing. The 

 lofty parallel ridges east of Burmah, in being medio-meridional, 

 are so far in conformity with the last-mentioned features. 

 This brief notice will scarcely permit of any reference being 

 made to the equatorial extensions from the Pamir through 

 Western Asia, &c. 



The question next suggests itself, arising from a consideration 

 of all the phenomena that have been noticed If the great pre- 

 Cambrian plateaux have always existed as masses, having an ele- 

 vation far above the bottom of the great intervening depressions 

 (ocean-basins), how have they become covered up with marine 

 sediments thousands of feet in thickness, and representing suc- 

 cessive geological periods ? In this connexion it may be argued 

 that elevations of rock-masses are of two kinds ; one due to 

 stratal disturbances, which for the most part have been exerted 



