THE ISOSEISTS. 3 17 



changes from one characterised by a preliminary tremor or tremors 

 followed by a sudden thrust or thrusts backward and forward that 

 instantly destroyed all buildings, as at Dharmsala to one that was a 

 regularly increasing single-movement vibration and much less destruc- 

 tive. The line of change corresponds to the passage from the Upper 

 Siwalik conglomerates and soft sandstones to harder and firmer forma- 

 tions until at Bajaura we are on the much more compacted old Hima- 

 layan series, and it also corresponds, as we shall see later, to what is de- 

 duced as the direction in which the axial centrum " pitches " or 

 increases in depth. 



Isoseist No. VIII. 



The VHIth isoseist is relatively a very well-marked one. It forms 

 two separate closed curves, one in the Kangra-Kulu 

 marked in two closed area and the other, a smaller one, in the Dehra Dun- 

 Mussoorie area. In both areas, but especially in 

 the main Kangra-Kulu area, the VHIth isoseismal is the boundary 

 where sensible damage to buildings begins to be plainly visible. On 

 entering that area the least observant of human beings would very soon 

 have seen that a disaster had occurred, whereas, avoiding the larger towns, 

 he might have wandered over the surrounding isoseismal zones for days 

 without encountering anything more noticeable than a few tiny cracks 

 in walls. 



(i) Kangra-Kulu area. 



Like the other isoseists, thi3 isoseist is more definite in position in a 

 Position and in- W.N. W. than in an E.S.E. direction. The curve 

 eluded area. cuts Telokenath (Mangla Devi) near Kotla, a point 



between Dera Gopipur and Jawalamukhi, Suket and Rampur ; whilst in 

 its northern curve it cuts less definitely a point between Naggar and 

 Manali, another a little east of Manikarn and a third at Gaora near 

 Rampur. The included area is about 2,150 sq. miles, and it forms an 

 elliptical belt round the IXth isoseist. To the north of the Dhauladhar 



