50 rooTE : geology of maditea and tinnevelly districts. 



into typical conglomerate. Associated with the shingle are occasional 

 flakes of brown, buff, or greyish chert of foreign origin, some of •which 

 certainly seem to have been trimmed for use as scrapers or knives. 



Coming south of the Vaigai we reach the Mudukan Kulam (Moodoo- 



cumcolum) tract (No. 8) which I have named after 

 Mudukan Kulam tract. , . i , • 



the village givmg its name to the only trigonome- 

 trical station shown on the map (sheet 80) in that region, as no more 

 important place lies within the limits of the patch in its typical and un- 

 mistakable portion. The tract is a long and narrow one lying between 

 Prevalence of gravels ^^6 alluvial valley of the Vaigai and that of the 

 and sands. Q undai and extending a distance of about 36 miles 



from north-west to south-east with an average breadth of 8 or 9 miles. 

 Thoughout by far the greater part of this tract the lateritic beds show a 

 gravelly or sandy and but slightly ferruginous character. The hard con- 

 glomeratic variety occurs only in small patches here and there, all in the 

 northern half of the tract. None of these patches are worth separate 

 mention, but they are indicated in the map by letters. The sandy parts 

 consist generally of pale reddish or reddish-white sands with a variable 

 quantity of ferruginous pellets of concretionary origin. Included gravel 

 or even coarse shingle is frequently met with in the northern part, not 

 go much in distinct beds as distributed through the general mass of sand. 

 These o-ravelly beds had formerly a very much greater extension 

 Former western exten- westward, and considerable remnants of them 

 sion of gravelly beds. remain scattered over the gneissie rocks, but in 



patches too ragged and too much interrupted by protruding masses of 

 the gneiss to admit of their being separately mapped on the small 

 scaled map (4 inches to the mile), which alone is at present available for 

 the Madura country. Several such patches of gravel are noteworthy on 

 either side of the Gundar valley close up to Tirumangalam and 

 at intervals for some 3 or 4 miles northward of that place. 



By far the greater quantity of this gravel consists of rolled granular 



quartz rock derived from some of the many out- 

 Niiture of the grixvels. n ,i , ,• i p xi. 



crops 01 that very peculiar member or the gneissic 



( 50 ) 



