Dec. 1861,] 



Geology of the Neilgherries. 227 



latter has a gangue of compact Felspar, embodying small crys- 

 tals, of various minerals. It approximates to the Elvan of the 

 Cornish Miners. My friend Doctor Burrell detected this rock 

 cropping out in the Fort ditch, associated with Gneiss, Horn- 

 blende Rock, and Limestone. 



Neilgherries. 



The labours of De Benza and others have thrown considerable 

 light upon the Geology of the south and west districts of these 

 Hills. To the north, and east, there is an extensive scope remain- 

 ing for further research. To these points I shall principally direct 

 my attention. 



I briefly premise by sajing that the absence hitherto of Se- 

 condary and Tertiary Rocks, as well as of organic remains, has 

 induced the belief that the Neilgherries were elevated at a period 

 long anterior to the existence of those formations. 



Soils.— -Beneath the vegetable soil is a diluvial stratum (here- 

 after to be noticed), super-imposed upon a red soil ; obviously the 

 decomposition of the Hypogene Rocks subsequently indurated 

 into a wackke. 



The best proof I can adduce to this notion, is a section of the 

 Hill at the point where the surplus waters of the lake at Ootaca- 

 mund are discharged. In wet weather the Geologist may discern 

 in this mass of clay, striped and mottled with a variety of colors, 

 the remains of Granite, Greenstone, and Syenite. In some places 

 white bands traversing the mass, indicate what was once a mass 

 of quartz ; in others a black substance crossing the bed denotes 

 the former existence of a trap vein. At places where the rocks 

 have had Felspar for their principal ingredient, the clay becomes 

 a Kaolin (Porcelain clay), this is used for white-washing the houses 

 on the Hills. 



White, yellow, and red are its colours, derived from the varying 

 proportions of the iron in the Hornblende entering into the com- 

 position of the old rock. The wackke occasionally passes into a 

 Tufa, colored yellow by oxide of iron which soils the fingers. 



Masses of a white mineral are met with on the sides of the Hills, 

 that considerably resembles indurated Lithomarge, It adheres to 



