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Memoir on the Geology of the 



[Oct. 



visited but very few localities in India where these rocks prevail, I 

 cannot positively say whether or not the result of their decomposition 

 in both localities be the same*. But, this is certain, that the causes, 

 which may have contributed to decomposition in one place, do not exist 

 in the other : of that class are cold, damp, frost, elevation, &c, which 

 are not found in the low lands. Besides, is this decomposition the 

 efivct of existing causes, or the consequence of time and revolutions 

 gone by ? 



Here I must remark, that in some localities, such as near the bund 

 of the lake, on the road below the church, above the bazar, &c. the 

 red earth assumes the composition, texture, and appearance of real 

 lithomarge. 



As I have proposed to abstain from speculations, and from farfetched 

 theories, I shall not enter into any hypothesis respecting the causes of 

 this decomposition. It is enough to have noted a geological fact, which 

 requires but simple inspection to be certain of its existence. I shall 

 therefore proceed to describe some minerals, which are found imbedded 

 in the red earth ; some of which might prove very useful and advanta- 

 geous in the arts. Such is the porcelain earth, found in enormous 

 beds, and of the greatest purity, in this locality. 



This mineral is evidently derived (as it is almost in all places where 

 it is found in Europe) from the decomposition of the pegmatite or gra- 

 phic granite, which is chiefly met with in primitive districts. As this 

 rock does not appear to be common on the Neelgherries, I found it dif- 

 ficult, at first, to account for the origin of the numerous and thick beds 

 of porcelain clay. It was after visiting and examining the summits of 

 some of the highest hills, that I found a variety of pegmatite forming 

 many of the most prominent rocks on them. Such are the summits of 

 Doodabetta, Elk Hill, Kaitee pass, some of the peaks of the Koondah, and 

 probably many other places which I did not visit. 



It is undoubtedly to some of the erratic blocks and rolled masses of 

 this rock, or to the decomposition of those beds of pegmatite, into 

 which the true granite of the high hills seems to pass, that the porce- 

 lain earth is owing. Of these blocks, still in an undecomposed state, 

 we see many in the valley of Kaitee derived, in all probability, from the 

 summit of Doodabetta, or from that of the rock of Kaitee where the peg- 

 matite is seen in situ. 



By comparing a piece of this porcelain earth, just taken out of the 

 bed, with a piece of the hard pegmatite rock, one cannot but be con- 

 vinced of their being the same rock ; the one in a hard, the other, in a 

 decomposed state (No. 11). The pieces of the crystalline smoky 



* Doctor Heyne says, " a red soil prevails where sienite forms the apparent ground 

 rock."— Tracts Historical and Statistical on India, page 349. 



