Chap. I.] economic geology. 213 



In the South Arcot district, a fine plastic clay occurs in the Cuddalore 

 beds near the South bank of the Guddalum, opposite to Punrutti, and is 

 exposed by the side of the road leading Southward from that place. It 

 contains a small quantity of iron and lime, and owing to the former, has 

 a pale flesh tint, which becomes darker on burning. It is soft and 

 extremely tenacious. 



Cornish stone, from which a somewhat ferruginous kaolin may be 



„ . , , , , obtained by washing, occurs at Semangalum, close 



Cornish stone and kao- j 01 <=> j 



^^- to the borders of the Cretaceous and Cuddalore 



rocks 6 miles North of Yaludayur (near Pondicherry). It is only seen in 

 a well to the West of the village, the debris from which consists entirely 

 of the material in question. The well is about 20 feet across. It is impos- 

 sible to say how far the rock extends beyond, as nothing is seen in situ 

 anywhere around. It is probably a broad vein of Pegmatite running- 

 through the gneiss, such as are frequently met with in the surrounding 

 country. 



The granitic ridge to the North of the Cauvery contains a large quan- 

 tity of felspar, and this mineral might be easily 

 obtained free from any admixture of quartz. 

 Large quantities are scattered over the stony parts of the ridge, and 

 might be collected at small cost. It is apparently an orthoclase, but it 

 has not yet been analysed. 



Flints, almost undistinguishable from fragments of English chalk 



flints, are found at Coorchycolum, a village in the 

 Flints. ' J ' o 



North-east of the Trichinopoly district, a few 



miles South of the Vellaur. They occur in the highest part (exposed) 



of the Cretaceous rocks, near the overlap of the Cuddalore beds, and 



probably form a continuous band running North and South ; as I found 



similar flints to the South-east of Sainthoray,at a place the bearing of which 



from Coorchycolum is about that of the local strike of the bedding. The 



country is, however, too thickly covered with soil to admit of the flint 



