1836.] 



Neelgherries and Koondahs. 



271 



uniformly of the same colour and composition as the hornblende rock, 

 the strata (except they be of felspar or quartz, or of both) are not 

 distinguishable in the crystalline fracture ; the stratification is seen 

 when the minerals are exposed to the action of the atmosphere or 

 decomposed. In this state they are so clearly and so decidedly 

 marked, that one would hardly believe the decomposed to belong to 

 the same rock as the crystalline. Even in the greenstone itself, though 

 apparently an intimate, uniform and unstratified assemblage of two 

 minerals, when converted into lithomargic earth, the felspar is rendered 

 more discernible, not only when mixed with the hornblende, but also 

 forming intricate reticulations through the rock, which were not visible 

 in its former crystalline state. 



We see the first change to be in the colour of the stone some inches 

 into its substance, which, while still compact, has assumed a white cir- 

 cle of some inches thickness, produced by the felspar becoming opaque 

 and losing its compactness. In the circle which follows, encom- 

 passing the first, and which I call the second stage of decomposition, 

 the rock has lost a good deal of its compactness, retaining, however, 

 enough to be occasionally employed for temporary architectural pur- 

 poses (No. 103). The thickness, to which this second stage of de- 

 composition reaches in the substance of the stone, varies exceedingly, 

 from a few lines to many feet ; and, in the majority of instances, it 

 pervades the whole mass, whatever may be its volume. When 

 this happens the whole block not only proceeds to the second stage of 

 decomposition, but passes into the third, or lithomargic earth. These 

 three different stages are seen, in the most distinct way, near the bund. 



I cannot omit mentioning, in this place, the mistake committed by 

 many persons in taking for laterite, these rocks both in the second 

 and the third stage of decomposition ; the one in the compact state, the 

 other in the decomposed— an idea, which has embarrassed geologists 

 regarding this rock peculiar to India, and will continue to embarrass 

 them, so long as people, who ought to know the importance of giving a 

 correct name to facts and to things in all sciences, particularly in geolo- 

 gy, will not take the trouble to multiply observations, and are careless 

 in the discrimination of rocks, considering two substances analo- 

 gous, because of a similarity in colour or texture. We hope that our 

 Secretary, who appears to have taken up the subject earnestly, will 

 have opportunities and facts offered to him to dispel the ambiguity 

 which rests on this subject. I have already given my opinion on this 

 intricate question. 



Following the Koondah road, in less than a mile we come upon 

 the continuation of the magnetic iron ore, which, intersecting the lake, 

 extends to this place, very much alteredin appearance and composition, 

 looking more like a stratified ferruginous sandstone, than the continu- 



