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



i 



hills to the north might be raised, and this elevation, though 

 a secondary effect, might do more damage at Katmandu than 

 the earthquake itself could do at Gorakhpur, which is protect- 

 ed by some miles of soft blanket of sediment underneath. In 

 the Dharmsala earthquake Middlemiss estimated its depth to 

 be between 12 and 40 miles. Middlemiss's maximum value is 

 not very different from the geodetic value. 



It is an interesting question to consider whether a fissure 

 in rocks could extend downwards to a great depth. From a 

 place near the Indus in Kashmir it is possible to see a con- 

 tinuous wall of rock 4 miles in height, on the flank of Nanga 

 Parbat. Mount Everest stands erect 5| miles above sea-level ; 

 its summit stands firm and rigid 11 miles above the depths of 

 the Bay of Bengal. We have therefore evidence that the mate- 

 rials of the crust are strong enough to admit of the continued 

 existence of great differences in altitude. 



But Mount Everest is standing in air, whereas a crack in 

 the sub-crust becomes filled with rocks falling in and with 

 fluid rock magma from below : and the walls of the crack 

 thus get a support that Mount Everest does not possess. It 

 seems to me quite possible that a crack such as I have described 

 may have extended down to a depth of 60 miles by successive 

 fractures at increasing depths, the opening being filled by fall- 

 ing material. 



Internal Causes of Mountain Elevation. 



I have shown you how zones of subsidence in the crust are 

 bordered by mountains, and I have now to discuss the rela- 

 tionship of subsidence to elevation, of troughs to mountains. 

 The Red Sea is a zone of fracture, and it is bordered on each 

 side by a zone of elevation. But along the Bombay coast the 

 zone of subsidence is bordered only on the one side by a zone 

 of elevation. The sub-crustal crack from Surat to Cape 

 Comorin has been accompanied by a vertical uplift of the 

 Ghats, and I suggest for your consideration that the vertical 

 force which elevated the Ghats was the expansion of the under- 

 lying rock due to physical or chemical change. 



Mr. Hayden informs me that the specific gravity of the 

 rock composing the Neilgherries varies from 2*67 to 3-03, that 

 is 14 per cent, and that the rock of the Hazaribagh plateau 

 varies from 25 to 3*1, 24 per cent. 



The Western Ghats appear to have risen about 4000 feet. 

 Now we know that the Western Ghats are largely compensated 

 by underlying deficiency of density ; if the compensation of 

 the Western Ghats extends downwards to a depth of 60 miles, 

 then an expansion of two per cent would be more than suffi- 

 cient to account for the elevation of the Ghats. Mr. Hayden 

 finds variations of 14 and of 24 per cent in the densities of 



