38 FOOTE : GEOLOGY OF MADURA AND TINNEVELLY DISTEICTS, 



of Shabkotai (Shawcotta) and in the streets on the western side of the 

 town where the ground falls steeply. The whole of this tract of country 

 is thickly covered with massive later ite which masks all the underlying 

 rocks ; indeed not a single natural section was seen in which the relations 

 of the laterite to the Cuddalore beds could be studied, while the artificial 

 sections in temple tanks and wells were far too limited in depth 

 and extent to be really satisfactory, even where the presence of water 

 did not prevent the base of the sections being visible. 



The most southerly outcrops of grit beds within the limits of the 

 Shahkotai tract was seen at Oodoopooputty 10 miles south-west-by- 

 south of Shahkotai where a white and yellowish-brown mottled grit is 

 exposed underneath the laterite in various small rain gullies. The grits 

 are exposed only to a depth of 4 or 5 feet at the utmost. 



No gritty beds were seen in the Seruvayal (Serruvial), nor in the 

 northern and eastern parts of the great Sivaganga tract. In the 

 western part, however, are several outcrops of sandstone and grits refer- 

 able to the Cuddalore group. The first of these requiring to be noticed 

 occurs about 1^ miles south-east of the town of Sivaganga. Here 

 several beds of hard thick-bedded grit crop 

 out from below the general lateritic covering of 

 the country. In colour the rock is dark purplish-grey with brown 

 bandings, and the dip is about 20° to the north-east. Much diagonal 

 or " false '"' bedding is seen in the freshly-broken rock, which is over- 

 laid conformably to the eastward by less compact dark-brown and 

 yellow-brown gritty sandstone. The hard grits, which are largely 

 quarried, are so tough as to require blasting. Unfortunately the re- 

 lation to the lateritic beds cannot be ascertained as the latter are locally 

 absent. About 5 miles to the south-south-west of Sivaganga is a con- 

 Section soutb-south- siderable exposure of brown gritty sandstone 

 west of Sivagmiga. which forms the upper part of the low scarp over- 



looking the narrow strip of gneiss rocks which there divides the grits 

 and laterites from the great alluvial flat of the Up-Aru (Hoop-Aur) 

 and A^aigai rivers. It is a sandstone of very peculiar appearance, a 

 ( 38 ) 



