26 Rev. 0. Fisher on Variations of Gravity and their 



been done roughly for More and Kaliana, because they have 

 been already calculated and published. But it will be observed 

 that the attraction of the "roots " of the masses cannot be 

 discovered from that of the masses themselves, except in the 

 case of plains. 



At the two former of the " very irregularly surrounded 

 stations/' Dehra, Mussoorie, and More, we shall make no 

 attempt to calculate the attractions, and conclude with some 

 remarks upon certain stations in Peninsular India. 



There are no true mountain-ranges in Peninsular India, the 

 so-called " mountains " being only the escarpments of plateaus 

 which have escaped denudation. " Peninsular India is, in 

 fact, a tableland, worn away by subaerial denudation, and 

 perhaps to a minor extent on its margins by the sea." * The 

 Deccan traps are of Lower-Eocene age, covered in places by 

 nummulitic rocks|. Their total thickness maybe 6000 feet {. 

 The horizontality of the flows in these plateaus is remarkable. 

 In considering the bearing of the gravitational phenomena at 

 stations in this part of India, we ought to take its structure into 

 account. No root has been formed by compression during 

 the formation of its hills. As the country became gradually 

 weighted by flow upon flow of the basalts, the crust must 

 have sunk gradually into the magma. The Geological Survey 

 does not appear to have yet mastered the details ; but possibly 

 it will be found that the country is faulted, and consequently 

 deep roots will answer rather to low elevations than to high 

 ones, and the equilibrium will be of the tract as a whole, 

 instead of being established within every vertical boundary. 



In any case where the attraction of the mass above the sea- 

 level, may be justly taken as due to an infinite plain, it appears 

 by our formula that the negative attraction of the root would, 

 on the hypothesis of hydrostatic equilibrium being established 

 within every vertical boundary, exactly balance it ; and the 

 resulting local attraction at the station ought to be nil. Now 

 there are seven stations of the great arc between latitudes 16° 

 and 24° N. which are upon the basalt, viz. from Pahargarh to 

 Kodangal inclusive ; and the local attractions, relative to the 

 attraction at sea-level at Punnse, in swings of the pendulum, 

 range for these stations, as shown in column 5, from —0*79 

 to + 1*75, being as below : — . 



* < Manual of the Geology of India/ by Medlicott and Blanford (Cal- 

 cutta, 1879), p. v. The contrast between the peninsular and Himalayan 

 regions is strildngly shown by a large model now on view in the Indian 

 Annexe of the Indo-Colonial Exhibition at South Kensington. 



t Ibid. p. 381. % Ibid. p. 308. 



