GRITTY SANDSTONES. 39 



curious system of shallow quasi-con choidal pitting"?, and the pittings 

 affecting the successive laminae so as to show on weathered edges a 

 columnar series of pittings super-imposed one above the other with a 

 fair approach to verticality. The pittings often leave shallow inter- 

 laminar spaces which are lined with a shining black film of oxide of 

 iron. The dip of the beds is not very clear, but they appear to dip 

 generally to the eastward at very low angles. They are covered up to 

 the eastward by thick, deep red, higlily ferruginous soil which is 

 followed still further east by large spreads of massive laterite which 

 covers all the high ground up to the new high road between Sivaganga 

 and Mana Madura. To the south-east of the brown sandstone outcrops 

 the ground continues high, and forms a long-stretched down run- 

 ning south-east for 7 or 8 miles. 



Where the Sivaganga-Mana-Madura road approaches the crest of this 

 Section 5 miles soufcli ^own from the north side, the laterite, which is 

 of Sivagunga. greatly developed, has the character of a very 



coarse conglomerate which lies on an equally coarse conglomerate with 

 gritty matrix. Both conglomerates contain many large and small 

 lobbies and some small boulders of granular quartz rock. The grit con- 

 glomerate is only exposed in a small well 1^ to 14 feet deep near the 5th 

 milestone south of Sivaganga. The lateritic conglomerate which shows a 

 maximum thickness of about 10 feet rests on a much eroded surface of 

 the grits, so that the two formations are certainly unconformable at 

 this place, whatever their relations may be elsewhere. The grit contains 

 many quasi-YevmiG\x\siV aggregations of coarse white or mottled clays. 

 A small show of coarse white or mottled grits occur in the bed of a 

 Manambakkam sec- i^^in guUey running westward into the Up-Aru, 

 *'^"* about half a mile northward of Manambakkam 



(Manambaucum), but the high ground to the east only show here and 

 there very fair sections of the lateritic conglomerate and the grits are not 

 exposed. The southern slope of the long down above referred to is 

 thickly covered with very richly ferruginous hard red loam which is 

 largely overgrown with low scrub jungle. 



( 39 ) 



