142 HOLLAND : GEOLOGY OF THE NEIGHBOURHOOD OF SALEM. 



and immediately around it. The former circumstance might very 

 well be the outcome of the latter, for in any great earth-move- 

 ments such a strong, homogeneous mass would more readily part 

 connection with the surrounding country than submit to internal 

 deformation. There is thus a prima facie reason for expecting 

 evidence of dislocation at the foot of such distinct and large massifs 

 as the Shevaroys and Nilgiris. 



Apart from the question of movements due to crust-folding, 

 it is questionable if uninterrupted denudation could proceed for such 

 long ages without disturbing the isostatic balance by its differential 

 effects. 1 



Besides the N.-E. — S.-W. dislocation lines which are so plainly 

 'exhibited near Salem, there is less satisfactory evidence of fracture 

 in a more northerly direction running along the western face of the 

 Shevaroys, and separating the normal charnockites from the basic 

 garnetiferous varieties of the Nagaramalai type. The peridotites of 

 the Chalk hills occur along this line, and if one could only be more 

 certain of the evidence outlined above as to the north-easterly dis- 

 placement of the Shevaroy mass, this mass of peridotite at the south- 

 west angle might be regarded as the accompaniment, if not in part 

 the cause, of the disturbance. Here, however, the deductions, in the 

 absence of sufficient evidence, approach mere speculation, and it will 

 probably be more profitable to allow the observations to stand in 



1 C. E. Dutton, " On some of the greater problems of Physical Geology." Bull. Phil. 

 Soc. f Washington, Vol. XI (1892), p. 51. For the condition of equilibrium of figure to which 

 gravitation tends to reduce a planetary body, irrespective of whether it be homogeneous or not, 

 Dutton proposed the name isostasy. Whilst pointing out that the earth's crust would not be 

 strong enough to permit any great departure from the isostatic condition, Dutton admits that 

 it is impossible to state with precision to what extent differential denudation and deposition 

 may be carried before producing movement towards the restoration of isostasy. Judgi ng by 

 the instances he quotes (and which show that the geological is more precise than the mathe- 

 matical estimate) a mass of rock covering 100 square miles and ranging between 3,500 and 

 5,500 feet above the surrounding country could not be maintained without deformation to 

 restore the isostatic balance. I expect we shall find that large homogeneous masses like the 

 Nilgiris, the Shevaroys and other hills in South India have, by this means, all become 

 separated by fault lines from the rocks of the plains around ; this may account for their very 

 steep scarps. 



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