90 



OLDHAM: THE STRUCTURE OF THE HIMALAYAS, ETC 



little affected, or in many cases not affected at all. Consequently we 

 may take it that the form of the underground floor of the Gangetic 

 trough is similar in kind to one or other of the two assumptions 

 involved in columns I and II of the table. We may be certain that 

 the Siwalik region does not cover a deepening of the trough ; but 

 whether the floor continues underneath it with very little change of 

 level, or whether there is a marked drop, and deepening of the trough 

 just outside the limits of the Siwaliks, cannot be determined from 

 the latitude observations alone. 



The gravity stations in the Siwalik region of the Dehra Dun 

 are seven in number, and for two of these only, Raj pur and Dehra 

 Dun, has the Hayford anomaly been published. A list of these 

 stations is given in table No. 27, where two other stations to 



Table 27. — Gravity 



stations in 



and south 



of ifie Deli 



ra Dun. 









Hayford 



Residue 



Station*. 



Distance 

 from main 



Bouguer 



compensa- 

 tion of 



expressed 



J iL t 





boundary. 



anomaly. 



Imaginary 

 Range. 



as depth of 

 Trough. 



Rajpur .... 







— 124 



— -073 



lf.,000 



Kalsi 



t) 



— -098 



— -073 



7,500 



Dehra Dun .... 



2 



— -126 



— -0(>7 



12,000 



Fatehpur .... 



(i 



— -100 



— -05G 



7,500 



Harchvar .... 



7 



— 114 



— -053 



10,000 



Asarori .... 



9 



— -112 



— -048 



10,000 



Mohan .... 



14 



— -104 



— -039 



10,000 



Roorkee .... 



25 



— -107 



— -024 



13,000 



Nojli 



38 



— -095 



— -015 



12,000 



the south are included, in order to bring the series into connection 

 with the stations in the alluvial plain, which have already been 

 dealt with. As before, the first column gives the name of the station, 

 the second its distance from the main boundary, the Bouguer 

 anomaly of gravity is given in the third column and the gravitation 

 effect of the compensation of the Imaginary Range in the fourth. 

 Finally the depth of the trough is given, to the nearest 506 feet, 

 on the supposition that the whole of the unexplained residue of the 

 anomaly is due to the defect in density of the material contained 

 in the trough. These depths were obtained from table No. 18, 

 where the effect of a 15,000 feet deep trough is given, the depth in 



[ 238 1 



