86 OLDHAM: THE CACHAR EARTHQUAKE OF 1 UTH JANUARY 1869. 



severe ; this starting near Gowhatti runs east to Nowgong, and then 

 curves down to Munnipur whence it turns westward and passes to 

 Silchar. 



An inspection of these lines shows that the dimensions of the area 

 included are much greater in a north-east and south-west direction than 

 in the co-ordinate direction of north-west and south-east. This of course, 

 to a certain extent, depends on the fact that no reports could have been 

 obtained from the country lying to the north of the southern boundary 

 of the Himalayan range, nor from all that portion of Burmah over which 

 the shock may very probably have been felt ; but yet the fact remains 

 that the area affected undoubtedly extended much further East and 

 West than North and South. This extension might have been produced 

 by either of two causes,— firstly, the structure of the country, which 

 mio"ht be such as would favour the transmissions of the shock further 

 in one direction than another ; and secondly, the direction of the fissure 

 from which the shock originated. We will examine the circumstances 

 of the case, and see to what extent the action of one or both of these 

 causes must be invoked to explain the facts. 



From the Jaintia hills in which the shock originated a range of 

 mountains composed of more or less hard and crystalline rocks extends 

 eastwards; through these cystalline rocks the shock would be trans- 

 mitted with great readiness ; but as we know neither the structure of 

 the country nor the effects of the earthquake in Upper Burmah with 

 sufficient detail, no further reference will be made to this portion of the 

 seismic area. To the north of the Khasi range, but separated from 

 it by the valley of the Brahmapootra, lies the range of the Himalaya 

 mountains. These are composed of indurated rocks well adapted for 

 the transmission of the shock ; this superior elasticity of the rocks 

 is to a certain extent counterbalanced by the fact that the shock would 

 have to cross the strike of the strata flanking the range, and its force 

 would therefore be lessened in passing from stratum to stratum ; but the 

 flattening of the isoseismal on the north is to a great extent due to the 

 absence of records from that region. To the south and south-west the 

 ( 86 ) 



