48 rooTE : geology op madura and tinnevelly districts. 



of Serruvayal. The sandy variety occurs only at the extreme south- 

 eastern extremity. 



South of the Serruvayal tract comes the Sivaguuga one (No. 7), the 



largest we have to describe. The spreads of 

 The Sivaganga;tract. ,i , j <? • i 4 j.i, i 



the hard terrugmous conglomerate^ though very 



common everywhere except on the extreme eastern side where a band 

 of from 3 to 3 miles in width of sands prevails, are less extensively con- 

 tinuous and more frequently covered with thick red soil. This appears 

 to be due to some extent to the greater extension of agriculture^ in favour 

 of whicli the surface of the conglomerate has in many places been broken 

 up with picks or crowbars to expose the softer sub-rock which, if not 

 allowed to solidify again by the action of rainwater, weathers into a fairly 

 fertile soil. The most typical developments of the conglomerate near Siva- 



. . -a- ^ g-anffa occur to the north-west and north of the 



Conglomerate at rv-a- tj o 



ajar Kovil. town. The environs of Kalayar Kovil (Calliar 



Covil) also show very typical spreads of conglomerate and of the deep 

 red fertile soil derived from it under favourable circumstances. 



A very typical spread of hard laterite conglomerate covers a large 

 area on the high ground lying 2 or 3 miles west 

 of Mangalam (Mungalum) and extends north- 

 eastward along the new high road from Shembanur to Sivaganga. 

 The hio^h o-round south-west and south of Sivaganga, and its southerly 

 extension past Mana-Madura almost down to the southernmost apex of 

 the Sivagunga tract, is covered with very typical laterite conglomerate, 

 which at intervals shows its true character very markedly by including 

 considerable numbers of rolled pebbles (large and small) of gneissic 



., ^ origin. This may be very well seen a little to 



At the 5tli milestone » j j 



Mana-Madura road. the south of the 5th milestone on the new road 



o-oino- direct from Sivaganga to Mana-Madura. The laterite conglomerate 

 here rests unconformably on the eroded surface of an old gritty conglo- 

 merate which on stratigraphical and petrological grounds I have referred 

 to the Cuddalore series (see page 39). The laterite conglomerate 

 attains a thickness of fully 10 feet and includes many well-rounded 

 ( 48 ) 



