LATERITIC FOEMATIONS. 49 



masses of granular quartz rock, some of them large enough to deserve 

 the appellation of small boulders. 



A couple of miles to the south-west the laterite also shows many- 

 included pebbles of granular quartz rock lying about on the surface 

 (apparently washed out of the mass). 



I noticed also sundry angular fragments of a brown chert foreign 



to that part of the country. Similar angular 

 At nearMana-Madura. » -i • i i 



fragments of an identical chert were noted also 



in rain-gullies on the top of the scarp of the laterite plateau to the east 



of Pikulam (Pecolum) 3 miles south-south-east of Mana- Madura. The 



extreme south end of the Sivaganga tract of laterite rocks is skirted by the 



Vaigai river, but unfortunately no section has been formed by the river. 



There is a very considerable overlapping of the laterite formations 



on to the gneissic rocks westward of the bound- 

 Outliers of laterite on . . i ri 

 the gneiss north of the aries ot the various tracts now enumerated. Scat- 



^^^^'' tered shingle forming the debris of one conti- 



nuous bed is widely spread over many parts, while patches of the hard 

 ferruginous conglomerate are also to be seen in various places. Con- 

 siderable remains of such shingle beds are to be seen to the west and 

 north-west of Melur, e.g., at Mankulam (Mauncolum) 6 miles to the 



Lateritic shingle west west, and again a little to the south and south-east 

 of Melur. ^f ^j^g great Allagiri temple at foot of the Allagiri 



hill. The shingle here, which is very coarse, is stained of a deep red, 

 proving that it was once embedded in a highly ferruginous matrix. It 

 is scattered over an area of several square miles in extent. Many patches 

 of ferruginous conglomerates are scattered over the gneissic plains to 

 the north-west and west of the Sivaganga laterite tract. 



To the north of Madura town considerable remains of a very typical 



^, ^, „„ , highly ferruginous laterite conglomerate rest on the 



North of Madura. , 



surface of the gneiss north of the Tallakulam 



(Tullahcolum) tank at a level high above that of the alluvium of the Vaigai 



river. A great quantity of shingle of gneissic origin is mixed with the 



ferruginous gravel, and in some places compacted by a ferruginous cement 



D ( 49 ) 



