272 



Crystalline Limestone. [No. 8, new seeies. 



III. On the occurrence of Crystalline Limestone in the vicinity of 

 Trichinopoly. By W. King, Esq., Geological Survey of India. 



(Communicated by Government.) 

 While surveying the Moosery and Toriore talooks of the Tri- 

 chinopoly District, I observed some blocks of Crystalline Lime- 

 stone in the bund of a tank near Comungalum. Subsequent ob- 

 servation showed that this rock occurs in situ in two places : at 

 Naivailie, about sixteen miles North-west of Trichinopoly ; and at 

 Mootum four miles further North and on the West side of the 

 Tyaur river. 



These two localities occur in a metamorphic district consisting 

 of beds of micaceous, hornblendic, and quartzose gneiss, more or 

 less foliated and in many cases particularly in the South-western 

 part of the Toriore talook assuming a perfectly schistose charac- 

 ter. They are situated almost on the Northern edge of a great 

 development of granite and quartz, either in the form of veins or 

 protruded masses, which forms a belt more than eight miles in 

 width extending along the Northern bank of the Cauvery from a 

 point North of Trichinopoly into the Coimbatore District. Gene- 

 rally throughout this granitic region the direction of the foliation 

 of the metamorphic rocks is E. N. E. = W. S. W. while the aver- 

 age dip of the beds is 45° to the North. 



At Naivailie the limestone appears at the Eastern end of the 

 tank as a bed 6 or 7 feet in width cropping up between bands of 

 gneiss. From this point it extends in an E. S. E. direction for a 

 little more than a mile, where it takes a new direction E. N. E., 

 and so continues for another mile. Here another band joins it 

 which may be a continuation of a smaller one occurring at Naivai- 

 lie about 100 yards North of the first. 



Throughout the greater part of its extent the main band pre- 

 serves an uniform thickness of 6 or 7 feet, but widens out at one 

 place (where there is a large granite vein and much contorted 

 gneiss) into a surface of more than 50 yards square. The bedding 

 of the gneiss rocks in the vicinity is quite distinct, the dip being 



