316 LIEUT.-COLONEL S. G. BURKAKI) ON THE 



on the north by mighty mountain ranges and tablelands. Deficiencies of density 

 underlying and compensating the highlands, on whatever assumptions of depth they 

 may be based, will be found insufficient to account either for the prevalence or 

 mao-nitude of these southerly deflections; that the mountains and deflections are, 

 however, in some way connected can hardly be doubted. The section in fig. 3 

 of Plate 14 perhaps justifies the inference that the general deflection of gravity 

 towards the south is being caused by deficiencies, underlying not the mountains 

 themselves, but the plains in the immediate vicinity of the mountains. 



All our pendulum and plumb-line stations situated actually in the Himalayas have 

 so far been located on peaks ; the results deduced have therefore been obtained from 

 the highest points in the several Himalayan districts visited. It is important that 

 observations should be taken at stations situated in the deep valleys of the inner 

 Himalayas. The difficulty of fixing such stations by triangulation has hitherto 

 limited observations to summits, but it is necessary now that we should ascertain 

 whether the subterranean deficiencies underlying the Himalayas vary in amount with 

 the heights of the superincumbent mountains, or whether in their compensation of 

 the mass as a whole they remain independent of the altitudes of the alternating 

 ranges and valleys above (see fig. 2, Plate 14). 



Another question of interest has arisen, namely, whether the southerly deflections of 

 the second region merge gradually along the border line into the vertically of the 

 third region, or whether there does not exist an intermediate longitudinal area in 

 which northerly deflections prevail. A study of Table IVc. will show, I think, that 

 throughout a strip immediately south of the dividing line the deflections have a 

 tendency to be uniformly northerly.* The cross-section in fig. 3 of Plate 14 shows an 

 excess of mass to underlie Kalianpur (Station No. 24), and this excess is possibly a 

 contributory cause both of the southerly deflections of the second region and the 

 northerly deflections in the parallel strip. The continuance of similar deflections both 

 to the east and to the west of Kalianpur lead me to think that the pendulum 

 observations of the future will furnish on all Himalayan meridians cross-sections 

 similar to that given in the figure. 



Geodetical observations have shown that the density of the earth's crust is 

 variable, but they have not given any positive indication of the depths to which these 

 observed variations extend. All calculations of the effects of subterranean variations 

 in density and of mountain-compensation have, therefore, to be based on arbitrary 

 assumptions of depth. The fact that the plumb-line seems generally to respond 

 readily to results given by the pendulum, perhaps justifies the inference that the 

 observed variations in the density of the earth's crust are not deep-seated. If an 

 abnormal amount of matter exists in the crust near the surface, it will exercise direct 

 effects upon plumb-lines and pendulums in the vicinity, but if it lies at a great depth, 

 its effects, especially on plumb-lines, will be less perceptible. 



*Vide stations Chaniana, Valvadi, Badgaon, Aiikora and Mai. 



