1844.] Memoir on Indian Earthquakes. 965 



cond class, the shocks of the 9th February 1841, and 5th March 1842, 

 may be referred to. In the former case the shock is described as hav- 

 ing been " sharp and stunning, as if a blow had been struck under 

 you;" and in the latter, the observer felt as though he had received a 

 severe blow from behind, and been impelled forward. 



c. A sensation of tremulousness, without any defined motion or 

 concussion. This feeling ordinarily follows great shocks, when the 

 crust of the earth seems to be gradually subsiding from intense distur- 

 bance to its former state of quiescence. The inhabitants of the valley of 

 Cabool, distinguish this merely tremulous shock by a peculiar term 

 calling it, " Zill-Zillie," in contradistinction to " Goozur," which 

 appears to be the word used for the first class (a) ; numerous instances 

 of class (c), occur in the register, among which may be mentioned the 

 central Himalayan shocks of the 18th August and 23d September 

 1832, the lateral Himalayan shocks which followed the great earth- 

 quakes of August 1833, and February 1842, and the shocks in the 

 delta of the Indus from the 18th to the 26th June, 1819. 



d. The next characteristic of the shocks to be noticed, is the method, 

 of propagation. There is evidence of two varieties of this, (1,) when 

 the shock traverses a zone of the earth's surface, the breadth of which 

 is very small as compared with the length ; (2), when the shock is 

 propagated on all sides equally as from a central point ; the difference 

 between the two varieties arises in all probability from difference of 

 physical structure in the localities affected by the shock. The cases 

 illustrating the first, as for example, the shocks of February 1842, 

 or August 1833, occurred in the vicinity of great mountain ranges 

 where faults and disturbances of the strata are numerous. The shocks 

 were propagated in directions parallel to the mountains, and the breadth 

 of the tracts affected by them was but small. The most marked case 

 of circular propagation occurred in the alluvial plains of the delta of 

 the Ganges on the llth of November, 1842, and there, from the 

 greater continuity of the strata, less obstruction would occur to the 

 dissemination of the shock in all directions from the central point. 



That shocks, whether they affect zones or spaces which, though not 

 strictly circular, may yet for the sake of avoiding periphrasis be called 

 circles, are propagated from central points or lines of maximum intensity 

 is a fact so clearly established that it is scarcely necessary to advert to 



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