1843.] Memoir on Indian Earthquakes. 1043* 



The occurrence of Earthquakes is at present the only indication 

 furnished of the existence of disturbing forces beneath the Delta, but if 

 we may form a judgment from the results of the Boring operations in 

 Fort William, such forces must at no distant period have acted with 

 an intensity much greater than we have had any evidence of since we 

 became acquainted with India. The section of the Delta furnished by 

 these operations exhibits a series of strata alternately composed of 

 coarse gravel and fine river sand, or lacustrine mud, accompanied by 

 two remarkable deposits of carbonaceous matter, one near the lower, 

 the other near the upper extremity of the section. The lowest stra- 

 tum, attained at a depth of 392 feet from the present surface of the 

 Delta, and continued to 480 feet, consists of coarse conglomerate com- 

 posed of large rolled fragments of primary rocks. To this stratum, 

 on grounds as plausible as the circumstances of the case will admit, 

 Dr. McClelland has assigned an age of nearly 3,300 years. Since that 

 epoch, therefore, all the subsequent changes of level in the Delta, so 

 clearly intimated by the nature of its constituent, strata must have 

 taken place, and as in the latest of these changes, a subsidence of the 

 surface of the land to an extent of 75 feet in depth is indicated, it may 

 reasonably be inferred, that a high intensity must have characterised 

 the disturbing forces to which a change of such amount was due. 

 Those who may wish to examine the points just alluded to in greater 

 detail, are referred to my Memoir on the Structure of the Delta of the 

 Ganges in No. 3 of Dr. McClelland's Journal, where all necessary in- 

 formation will be found. 



8. — Earthquakes of the Eastern Coast of the Bay of Bengal. 



In tracing the geographical limits of the various volcanic regions 

 throughout the world, Mr. Lyell makes the great train of the Molaccus 

 to terminate abruptly with Barren Island in the Bay of Bengal, (lat. 

 12° N.)* But the entire eastern coast of the Bay of Bengal, as far to 

 the northward as Chittagong is essentially and prominently volcanic, 

 and along the Arracan coast especially are the indications of igneous 

 forces most distinct. To these I will subsequently refer more in detail, 

 but at present I must proceed to notice the Earthquakes which have 

 been experienced throughout this tract. 



Our acquaintance with the Arracan tract is comparatively speaking, 

 so recent, that the evidence of the frequent occurrence of Earthquakes 

 throughout it, is chiefly traditional and physical, and it is not until 

 the middle of the eighteenth century that we have the actual date of 

 any such convulsion, strictly ascertained. On the 2nd of April 1762, 

 however, a great shock occurred, affecting the whole of the eastern 

 coast of the Bay of Bengal, and extending to some distance into the 

 interior. The most ample details of the nature and effects of this 

 shock were observed in the vicinity of Chittagong, and are recorded in 



* In the map the sixth Edition of Mr. Lyell's work, which Lieut. Smith has evi- 

 dently not seen, the volcanic band is very properly carried on to Chittagong Eds. 



