36 FOOTE : GEOLOGY OF MADURA AND TINNEVELLY DISTEICTS. 



merates wliich^ excepting in one locality near Pondicherry/ have proved 

 perfectly devoid of fossils. To these sandstones, which in South Arcot 

 district, where they were first studied, rest unconformably on the 

 cretaceous rocks, the name of Cuddalore sandstones was given by Mr. 

 Henry F. Blanford/ who was inclined to think them of tertiary age. 

 Sandstones of identical characters occur largely near Madras and in 

 Nellore districts, while to the south of the typical spread near Cuddalore 

 a large extent of them stretches away from the valley of the Vellar 

 to the northern side of the Cauvery delta. These sandstones have not 

 been mapped separately from the overlying laterite, as they are only 

 exposed over very small areas with generally very ragged boundaries. 

 Moreover, it very often happens that from the base of the lateritic form- 

 ation being of similar gritty character, it is quite impossible in Ihe 

 absence of any organic remains to draw a boundary line between the two 

 formations. South of the delta similar soft sandstones and grits re- 

 appear in the neighbourhood of Tanjore and Vellam, while outcrops 

 of them are met with at intervals in the territory of the Tondiman or 

 Pudukotai Maharaja. The two last or southernmost of these outcrops 

 fall within the limits of the present memoir and map, and therefore 

 require full description. The first of these outcrops occurs on the western 

 slope of the low jungle- covered rising ground 7 miles east of Tirumayam 

 (Tirmium), known locally as the Shenkarai hill. Here an extensive 



series of rain gullies exposes, but unfortunately 

 Slienkarai section, ,, t ., • i ^ t p 



only to a very small depth, a considerable surface 



of gritty conglomerate which dips east-north-east or east-by-uorth at 

 angles of from 13° to 15°. False bedding prevails but only to a small ex- 

 tent for so coarse a rock. The conglomerate is of mottled brown 

 to pinkish and whitish less frequently reddish-yellow colour and 

 tolerably compact with gritty matrix including quartz and gneiss 



'At Tiruvakknrai (Trlvicary) where silicificd stems of large trees, some of them 

 coniferous, are to he seen imhechlcd. The coniferous wood has been described under the 

 name of Peuce Sehmidiana by ISchmidt and Schlcideu in their treatise Ucbcr die Natur 

 dcr Kicsel Iloelzer, Jena, 1855. 



2 Sec Mem. G. S. I., Vol, IV. 



( 36 ) 



