204 



Notes, chiefly Geological, on the Coast of Cor omandel, from the Pennaur to 

 Pondicherry. By Captain Newbold. 



The coast from the mouth of the Pennaur to Madras, is a sandy 

 plain, covered with reddish sandy loam which occasionally passes into 

 clay, and generally rests upon the bluish-black marine clay of the Coro- 

 mandel. It has been already said, that the breadth of the latter stratum 

 varies, and is interstratified with layers of sand and reddish clays ; — the 

 whole resting usually on granitic or hypogene rocks : nodules and 

 masses of a concretionary sandstone are found imbedded in the sands 

 close to high-water mark, often perforated by lithodomi. Magnetic iron 

 sand is found in many situations mingled with the sea sand, derived 

 probably from the hornblende and basaltic greenstone rocks. This iron 

 sand occasionally, I suspect, contains potassium, and strongly resembles 

 iserine in external character. 



Farther inland, between the base of the ghauts and the sea, extend 

 thin beds of laterite, and sandstone closely allied to laterite, passing 

 into puddingstones and soft shells of various colours. 



The puddingstones usually imbed rounded pebbles of white quartz, 

 and of the older sandstone which crests the eastern ghauts near Nag- 

 ghery, Udegherry, &c. 



The beds of this sandstone rarely exceeds three or four feet in thick- 

 ness, and may be seen near Sri Permatoor, on the great western road, 

 (vide Notes from Mangalore to Madras), and, according to native infor- 

 mation, in the vicinity of Parmaulnaigpet, about six and a half 

 miles to the E. by S. of Tripassore, a little north of the road to 

 Madras. Their continuity, and that of the laterite beds, with which 

 they are probably contemporaneous, has been much interrupted by 

 aqueous denudation, which probably took place while the Coromandel 

 Coast was emerging from the bed of the sea. 



It is also probable that these sandstone strata were once continuous 

 with those imbedding silicified wood at Pondicherry and Verdachellum 

 in south Arcot. 



These remarks are merely thrown out to elicit farther investigation 

 and research into the age, and extent on the coast, of these interesting 

 littoral deposits, by which we may be enabled, probably, to mark out 

 the ancient lines of coast formed, as the land gradually rose. 



