ECONOMIC GEOLOGY. 101 



Pudukotai State^ but is more hornblendic than any of tlie rocks seen at 

 those places. 



Turning- to the south again, the beauty of the pale highly silicious 

 granite gneisses of the Cape Comorin type, such as those quarried near 

 Kalligudi Chatram Railway Station and at the Waddukarai rock near 

 Satur, have already been mentioned above (page 23). 



In many places in both districts are the beds of granular quartz 

 rock quarried but only for road material or for rough stone, as it is- 

 perfectly useless for any other purposes. 



No use, except as rough stone, appears to be made of the fine crystalline 

 Crystalline limestone limestone at Pantalagudi (page 21), 35 miles south 

 of Pantalagudi, &c. ^f Madura, nor of any of the other fine limestone 



beds at Tirumal (14 miles south-south-west of Madura) or at Shenkotai, 

 8 miles south of Pantalagudi, though these beds could easily be made to 

 yield an inexhaustible supply of beautiful pale grey, grey and pink, pink, 

 and pink and green marble of high quality. 



The Pantalagudi marble had been noticed already in pre-historic times, 

 as blocks of it had been carried at least 3 miles distance to be used 

 with blocks of gneiss and others of laterite in the construction of a 

 group of Kurumbar rings lying to the south-west of Pantalagudi. 



The hard sandstone of supposedly Cuddalore age, which lies a couple 



of miles south-east of Sivaganga, is quarried to some extent as a building 



stone. The very coarse ferruginous, quasi schistose, sandstone which 



occurs on the west side of the Sivaganga laterite 



Coarse schistose sand- 

 tone flags used for Men- tract and about north-east of M annambakkam has 



been used in long pointed slabs to form small 

 '^ menhirs" or upright stones in the centres of some Kurumbar rings, 

 the other stones of which consist of rude laterite blocks. The tallest 

 of these three menhirs stands about 7 feet out of the ground. 



The gritty calcareous sandstones and the shelly limestones belonging 

 Marine sandstones and ^o ^^^ recent marine series are quarried in many 

 gritty beds. places, some of which have already been inci- 



dentally named, but others have now to be enumerated. Beginning at 



( 101 } 



