NOTE ON THE LATEKITE OF OUISSA. ' 293 



are similarly found dispersed through the soil in places. They are 



frequently, as in the Tributary Mehals of Orissa, used as iron ore by 



the natives,* » 



The source of the nodules first mentioned is possibly this. Let us 



. , , , c ii, ■ ^ suppose a metamorphic rock of the average con- 

 And the mode of tneir ^'^ '■ => 



formation. stitution of those forming the greater part of the 



surface of Eastern India to be gradually disintegrating by the action 

 of the weather. It contains felspar, hornblende, quartz, magnetic iron, 

 and a little mica. The felspar and hornblende become, by weathering, 

 clay or a similar substance ; the quartz splits up into sand. The violent 

 tropical rains pour down upon the mixture ; the fine sand, the clay, and 

 the mica are easily washed away, the coarser sand remains, and, with it, 

 the magnetic iron, in virtue of its high specific gravity, like ore on the 

 washing floor of the miner. This magnetic iron is partly in small lumps, 

 partly in fine particles, and although its indifference to the action of the 

 weather has enabled it to resist the influences which have decomposed 

 and carried away the minerals which accompanied it, it, in its turn, 

 becomes subject to the changing action of meteoric watei's. It com- 

 bines with oxygen and water, and is gradually converted into the hydra- 

 ted peroxide of iron, and, in the change, it agglutinates the surrounding 

 sand more or less firmly. The nodules which are black and metallic 

 inside are those which, having been originally most compact, have 

 undergone the least change. Those which contain angular fragments of 

 quartz, or small pieces of partially decomposed gneiss, are formed by the 

 agglutination of the surrounding sand by the iron oxide in process of 

 change. Those, lastly, which have a concretionary structure, may owe 

 it to the gradual change of the mineral composing them, the alteration 

 having proceeded slowly and uniformly from their surface towards their 

 centre, or they may be true concretions, formed by the peculiar ten- 



* Eeport on tlio Talcheer Coal Field. Ante p. 71. 



