498 Notes, chiefly Geological, [No. 163. 



which is studded with numerous trunks, and often verdant with rice 

 and raggi cultivation. 



Plantations of the betel-vine and patches of sugar-cane are scattered 

 here and there, and tall groves of cocoa-nuts and palmyras tower over 

 an underwood composed chiefly of the dwarf date, cactus, euphorbia, 

 and mimosa. These form a low jungle covering the higher sterile, dry 

 patches, which intervene between the lower cultivated portions. 



Soils. The surface soil is usually sandy, and many extensive tracts 

 are entirely covered with a fine sand resembling that of the sea, and 

 lateritic debris. The sandy soil occasionally passes into a silt and 

 fine red clay, largely used in pottery and brick-making. 



The subsoils are in some situations beds of kunker of various thickness, 

 of mhurrum, or disintegrated rock, and granitic and hypogene rocks ; 

 thin beds of grey marl overlie, near the coast, beds of a black clay im- 

 bedding pelagic shells of recent species, laterite, and a loosely aggre- 

 gated sandstone which passes into slate clays, both white and co- 

 loured, with oxide of iron of various shades. 



Of the rocks above-mentioned granite, gneiss, and hornblende schists 

 are found basing all the rest, occasionally rising above the surface, but 

 in general thickly covered. The granite near the coast is usually of the 

 variety termed pegmatite, being composed of quartz and felspar ex- 

 clusively ; above the surface it commonly appears in naked bosses, and 

 detached concentrically-weathering blocks. On approaching the base 

 of the mountains these blocks become more frequent, and are mingled 

 with similar globular masses of basaltic greenstone, outgoings of the 

 numerous dykes which prevail in the granite and hypogene rocks. Frag- 

 ments of quartz rock, chert, jasper, and sandstone also occur, more 

 or less rolled, derived doubtless from the Naggery beds. The gneiss 

 usually contains hornblende. 



Occasional beds of laterite occur. One I observed between Madras 

 and Poonamallee, which passes into a loose sandstone and felspathic 

 shale. Laterite has been employed in the construction of the fort at 

 Poonamallee and in the revetment of the old fort of Tripassore. 



Eastern Ghauts. The southerly line of Ghaut elevation appears to 

 terminate on the N. bank of the Naggery river, south of Hodgson pettah, 

 and farther west in the bluff peak of Naggery nose ; but it, in reality, 

 suffers a deflection westerly and southerly, forming a great mountainous 



