Chap. IV. 1.] metamorphic rocks. 75 



break in a very low ridge, to die away under the alluvial flats opposite 

 to Singilandapooram. 



As to the source whence came all these immense quantities of iron. 

 Original source of iron wliich in the form of mag-netic oxide associated with 

 " "*^^°' quartz laminae constitutes the numerous vast beds 



we have been describing, no conclusion can be formed. 



The quantity of extremely rich iron ore available from the various 



sources named for smelting purposes may be stated 

 Quantity available. . 



to be mexhaustible. Great part is obtainable by 



the very rudest methods of quarrying the surface ; indeed, mining 

 would not be necessary for a very long time. If regular mining be 

 adopted, many thousands of millions of tons of ore are at command. 

 Nothing, therefore, but the want of fuel will prevent this part of India 

 from being capable of supplying the world with a never-failing quantity 

 of the very best iron. 



The method of smelting the rich magnetic iron sand adopted by the 

 natives will be briefly treated separately in an Appendix, and a lengthy 

 account is given in the catalogue of the Government Central Museum at 

 Madras, compiled by Mr. Edward Balfour, of the Madras Medical Service, 

 when in charge of that establishment. 



With regard to the nature of the magnetic currents which occur in 

 Magnetic currents in *^®^^ great store-houses of magnetism, but little 

 "^^^ ^ ^' can be said, as they were found to vary much 



within very short limits, and would consequently have required a much 

 greater expenditure of time than appeared warrantable to devote to a 

 great number of observations, in the absence of delicate instruments. 

 When brought well within the influence of the currents, the needle gen- 

 erally oscillated violently, frequently rotating three or four times before 

 the perturbation lessened, when the needle generally settled with the 

 north pole deflected more or less eastward, and often coinciding with the 

 strilce of tJ<e iron led. In detached blocks, even at some distances from 



( -^97 } 



