CitAP. I.] ECONOMIC GEOLOGY. 209 



the stones are either laid together without mortar, or so little is used 

 that it is not seen at the surface of the work. A large tank (now dry) 

 at Naicolum, a few miles to the South of Ootatoor, is walled with beauti- 

 fully cut blocks of gneiss, which appear to be built together entirely 

 without the aid of any cement, and the same remark is applica- 

 ble to many of the chuttrums and the tnundapums, the roofs being 

 constructed of long blocks of gneiss, carried on joists of the same 

 rock, which in their turn are borne ou the elongated capitals of 

 the square columns, all, so far as can be seen, laid dry without mortar. 

 One of the finest examples of such structure I met with is an old 

 mundapum at Yungadumpett, a small village between Verdachellum 

 and Cuddalore. 



I have already pointed out some of the chief localities at which crys- 

 talline and sedimentary limestones are procurable, and a reference to 

 the body of the report will give many others in the case of the latter 

 rock. There is another form in which lime occurs in the Cretaceous 

 rocks, to which I have not yet alluded, and which may be noticed as 

 promising a valuable material for certain specific purposes, though as 

 Septaria and calca- J^t untested; I refer to the calcareous nodules, 

 which are very abundant in certain beds of the 

 Ootatoor and Trichinopoly formations, and which, so far as can be 

 judged without actual trial, are probably well adapted for the manufac- 

 ture of hydraulic cements. The chief localities at which these are pro- 

 curable are : in the gypseous clays to the East of Ootatoor, in which 

 nodules, from the size of a marble to that of a small melon, occur in vast 

 numbers, and may be had for little more than the expense of carriage. 

 Concretions of a somewhat similar chai-acter occur in a sandy clay in the 

 upper part of the Ootatoor group, near Coonum ; frequently enclosing fine 

 specimens of Nautilus. The bed containing them is exposed in the 

 broken ground to the West of the village, and also in the nullah drain- 

 ing the ridge between that jDlace and Moonglepaud3^ The nullah to 



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