Dec. 1861.] 



Geology of the Neilgherries. 



249 



4. A Felspar of a deep green color, in appearance approximat- 

 ing to the beautiful variety called Amazon stone. 



5. Blueish green Felspar with white stripes (probably cracks) 

 presenting in one direction a highly shining pearly lustre, and oc- 

 casionally opalescent like Labrador. 



6. Calcedony of white, yellow, green and blue colors ; stakc- 

 titic, dendritic, botryoidal, and massive in shape, lining the geodes 

 of cellular ferruginous quartz ; accompanying. 



7. Hyalite investing the sides of an empty geode. 



8. In the same quartz, lining geodes occur microscopical and 

 very brilliant prismatic crystals of some ore of iron, but so small 

 as to baffle analysis, probably limonite. 



9. Red iron ore, — a mineral extensively diffused in the neigh- 

 bourhood of Ootacamund and upon Dodabett, occurs in every stage 

 of decay downwards to a red iron earth. 



In one stage of this progress it presents the appearance of com- 

 mon red brick. 



I shall take some pains to describe this mineral upon which the 

 appellation of laterite has been also bestowed. 



It is of a red brick color, full of small cavities which probably 

 once held scales of oxide of iron. Is brittle. Is a combination of 

 silica, water and iron; the iron being a peroxide occasionally 

 blended with protoxide when the stone becomes magnetic. 



In some specimens metallic grains may be distinctly seen with 

 the lens. Before the blow-pipe after roasting, the result is taken up 

 by the magnet ; with borax gives the fading green color which de- 

 notes peroxide of iron. In the bulb tube disengages water. Up- 

 wards this ore may be traced through different specimens to the 

 scaly oxide of iron lamellated with quartz. 



The iron ore of these Hills occurs in various curiously shaped 

 forms, viz. 



Tubular, botroyoidal, mammillary, cavernous, in veins traversing 

 quartz which it alters to sandstone, in hollow balls, &c. 



10. Pisiform iron conglomerate an aggregation of the pea iron 

 ore described before, and which I should have mentioned contains 



