xcvi Journal of the Asiatic Society of Bengal. [N.S.. XII, 



surface strata may be ascribed to local variations in the verti- 

 cal expansion of deep-seated rocks. 



External Causes of Mountain Elevation. 



The Western Ghats are as mountains very small compared 

 to the great ranges that stretch from China to France ; the 

 former are an example of vertical elevation without any obvious 

 horizontal compression of the surface : the latter exhibit both 

 vertical elevation and considerable compression by lateral 

 thrust. In the Western Ghats expansion of the subterranean 

 rock seems to have uplifted the surface strata without disturb- 

 ing the latter, in the Himalaya the subterranean rock has 

 expanded to such an extent that it has burst through the sur- 

 face rocks in the form of granite, and in its protrusions it has 

 pushed aside the surface strata and helped to crumple the 

 latter. The troughs skirting the Western and Eastern Ghats 

 may have been caused by the mere cracking of the sub-crust 

 from cooling. But the Indus-Ganges trough is so large, and 

 the mountains to the north of it constitute so unique a protu- 

 berance that the idea arises that some external force must have 

 pulled the Himalaya northwards from India, and must have 

 torn into a great rent the original line of tension that had 

 opened under the Ganges plains. 



The Earth possesses a figure of equilibrium. If the Earth 

 was at rest, its figure would be that of a perfect sphere : as it 

 is rotating, the velocity of rotation has caused much extra 

 rock to be heaped up round the equator : the diameter at the 

 equator is 27 miles longer than the polar diameter. 



Sir G. Darwin thought that the Earth's velocity of rota- 

 tion was constantly being decreased by the Moon's attraction 

 upon our oceans ; he thought that the tides were tending to stop 

 our rotation, just as the Earth's attraction has entirely stopped 

 the Moon's rotation. If our rotation velocity is decreased, 

 the figure of the Earth changes and becomes nearer and nearer 

 to a sphere : water can flow from the equator to the poles at 

 once, and the oceans can immediately assume the new form 

 of surface suitable to the decreased rotation velocity. But a 

 superfluity of rock would remain at the equator, and the 

 straining of this towards the poles might cause cracks in the 

 Earth's surface. I do not presume to say that this is the 

 cause of the rent in the Earth's crust hidden below the Ganges 

 plains. All I wish to point out is that these mountains 

 appear, as if they had been pulled northwards out of the 

 Ganges- Euphrates- Mediterranean rent, and I show you some 

 reasons for believing that the Earth's figure may have under- 

 gone deformations. The astronomical cause of these deforma- 

 tions is hidden in the past history of the Earth. In the Per- 

 mian era an ice age occurred in equatorial regions ; if the Earth'- 



