1844.] Memoir on Indian Earthquakes. 967 



moved forward nearly a foot from its original position, and subse- 

 quently thrown back again ; these instances will serve to explain 

 the first kind of motion. 

 The second is : 



b. A vertical, or as many observers style it, an " up and down 

 motion", with no lateral movement. This variety was well marked 

 during the minor shocks that followed the great earthquake of the 26th 

 August, 1833. Dr. Campbell remarks, " many of them have been se- 

 vere, and throughout the whole courseof these visitations, therehave been 

 two distinct varieties observed in the character of the shocks ; all those 

 at the commencement were of the undulatory or swinging kind, the 

 others wanted the swell, and were a violent up and down shaking, 

 with little lateral motion.'* The shocks of the 4th October and 29th 

 November, 1833, which were severe, were of the vertical kind. 



c. The third kind of motion observed is a combination of the two 

 preceding, giving rise to an undulatory movement or swell like that 

 of the sea. This is by far the most common species of motion accom- 

 panying earthquake shocks, and is sometimes exhibited on a very large 

 scale, as during the Jellalabad earthquake of 1842, the Nepaul earth- 

 quake of 1833, the Scinde earthquake of 1819. The surface of water 

 in ponds and rivers frequently exhibited the undulation, as during 

 the Calcutta earthquakes of the 11th November, 1842, and the great 

 shock of the 2nd April, 1762, when the water in tanks in Calcutta 

 rose upwards of 6 feet, and formed large waves. 



In some instances the shocks commence with the vertical and ter- 

 minate in the horizontal motion ; this remark is illustrated by the 

 phenomena of the shock of the 11th November, 1842, as described in 

 Part I. p, 30. Two or three slight vertical shakes or heaves of the 

 earth occurred, followed by a strong horizontal movement; this pecu- 

 liarity seems to have been observed in Calcutta only; at other places 

 the movement is described as of the purely undulatory character. 



The undulatory motion has been remarked as invariably the most 

 destructive kind of shock. Thus Dr. Campbell remarks of the Nepaul 

 shocks in 1833, that the swinging motion was alone destructive to 

 property, while the vertical, from the greater noise and more rapid 

 succession, was the more terrifying. This difference of the two kinds 

 of motion is easily explicable ; the vertical shock merely raises th« 



