Chap. I.] economic geology. 217 



but was unable to discover their origin. The specimens were consider- 

 ably waterworn, they consisted of quartz with little nests of malachite, 

 red oxide, fahl-erz and native copper, and were of sufficient richness to 

 repay working, were there any quantity of ore equally good. The gneiss 

 around is much penetrated by little cracks filled with quartz and calc- 

 spar, and it is probable that the veinstone had been derived from one of 

 these, of unusually large dimensions. 



Ornamental Stones, &c. Under this head may be included the marbles 

 Shell marble of Ga- which I have already described under the head of 

 limestones ; and a few varieties of quartz of no great 

 importance, but some of which are worked to a small extent by the native 

 lapidaries at Vullam, in Tanjore, The only marble worked by the natives 

 as such, is the shell marble of Garoodamungalum, of which table-tops, paper- 

 weights, and similar ornaments are manufactured in Trichinopoly. When 

 polished it is of dark-grey color, and is marked, like the well known 

 Purbeck stone, with white sections of the included shells. 



Jasper of two varieties, the one a yellow and red stone, the other a 

 cream-colored porcelain jasper, occur in the Cretaceous rocks ; the former 

 near Olapaudy, in the bottom beds of the Gotatoor group, the latter 

 in the Trichinopoly group between Thaloor and Cullygoody. Pebbles 

 of rock crystal and smoky quartz, (Cairngorum,) are found in the 

 Cuddalore conglomerates at Vullam, and are cut by the natives of the 

 place into spectacle-lenses and also as jewels. Amethysts also are 

 frequently sold by the lapidaries here, but I found on enquiry that 

 they are all brought from Kungyam, in Coimbatoor. 



D 2 



