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THE POPULAR SCIENCE MONTHLY. 



Prof. Tyndall observes that, " where the acting force is small and 

 the time great, the result is a slow and almost inappreciable change." 

 Thus, great areas of land may be elevated or depressed. " But where 

 the intensity is great and the time small, sudden convulsion must en- 

 sue." Thus, in an instant, mountains may undergo a change of eleva- 

 tion, or be shaken to fragments, or tracks of land sunken and over- 

 flowed. In the delta of the Indus are extensive areas of level ground, 

 over which native villages were scattered, with fortifications and other 

 defences. Of these, the fort at Sindree is shown in Fig. V as it was 



Section of one of the Cibcflab Hollows. 



before the disastrous earthquake of 1819. 2,000 square miles of the 

 delta sank from six to 12 feet, and was thus overflowed by the sea. 

 The village of Sindree and its fortifications were upon the sunken area. 



Northward, about 5^ miles from Sindree, a range of very low hills 

 was elevated during the earthquake. It was seen over the expanse of 

 waters, and extended about 50 miles, with a breadth in places of 16 

 miles, and was called by the natives, " Ulla Bund, or the Mound of 

 God." 



In 1822, just half a century ago, an earthquake occurred^ in Chili, 

 of terrific violence, even for that region of convulsions. It was estimat- 

 ed that 100,000 square miles of land were elevated from two to seven 

 feet, the rise being greatest inland, and probably included a portion of 

 the Chilian Andes. The location of the force must have been at great 

 depth, perhaps not less than 20 miles below the base of the Andes ; 

 and it is probable that the entire superincumbent mass underwent a 

 change of level of from two to seven feet of perpendicular elevation. 



The earthquake at Lisbon, in 1*755, has impressed the public mind 

 more than any other in modern times. The shocks, one of which ex- 

 ceeded all the others in violence, continued six minutes. The moun- 

 tains near were shaken to their foundations, and everywhere split and 

 rent. No part of the city was seriously injured which was built on the 

 limestone or basaltic formations ; but the shocks were most violent and 



