226 On the Alpine Glacier, Iceberg, [No. 159. 



clay hardened by the oxidized iron of the mica and hornblende. 

 Now the block A, might either roll on to a gneiss, or any other crystal- 

 line schist at C, or become buried in the alluvion at D. It might be 

 set in motion not only by a stroke of lightning or an earthquake, 

 but by process of its own weathering or that of the boss beneath it, or 

 the washing away by the rain of the cement. The distance to which 

 it might roll would be in proportion to the height and inclination of 

 the boss on which it rests, the slope of the plane at its base, and its 

 own weight and roundness. 



In some cases the very rocks from which these globular masses 

 originated, and on which they rested, have weathered faster than the 

 block itself, and have crumbled into the mounds of angular gra- 

 velly detritus so common over the whole granitic area of Southern In- 

 dia, known to native cultivators and well-diggers under the names of 

 Mhurrum and Ghurrus, in contradistinction to the nodular lime- 

 stone gravel called Kunker. 



Amid this granitic gravel evidently formed in situ, in some places 

 near 80 feet deep, are occasionally found the hardest spheroidal nuclei 

 of granitic and basaltic rocks. These blocks have longer resisted the 

 decay which has worn down the rock of which they once formed veins 

 or dykes. Such is also the case in the angular gravel arising from the 

 weathering of gneiss and the other crystalline schists, in which gra- 

 nitic and basaltic greenstone so extensively occur in the shape of 

 dykes or veins. 



That this gravel has not travelled far is evident from the angular 

 nature of its component fragments, and that it is not the transported 

 angular gravel of a moraine, or iceberg, is evident from the fact 

 of veins of quartz, extending into it from the less weathered portions of 

 the subjacent granite, or crystalline schists from which it is derived. 

 The vein A A, in the diagram is of quartz, which though crumbling 

 like white sand under the pressure of the fingers, is still seen to pre- 

 serve its relative place and proper direction in the gravelly detritus 

 above B, from the subjacent gneiss. ( See plate, Diagram, No. II. J 



Ovoidal fragments of granite sometimes occur imbedded in gneiss 

 at considerable distances from any surface granite, which when ex- 

 posed by the decay of the imbedding rock, might in an apparently ex- 

 clusive gneiss area be difficult otherwise to account for than as a trans- 



