214 



Memoir on the Geology of the 



[Oct. 



many other localities, where I have remarked about it a most luxuri- 

 ant vegetation of innumerable ferns, of which the .roots are seen de- 

 caying into a black powder. 



In many places below this black soil, and sometimes under the vege- 

 table earth, we see thick beds of a yellow ochreous earth abounding 

 with silica (No. 4). Indeed, in some places, as at Kotagherry, it re- 

 sembles very much the yellow Venetian Tripoli, previous to under- 

 going preparation for the arts (No. 5). The geological position, how- 

 ever, of the two, differs very much — the Venetian Tripoli, which is 

 brought there from Corfu, and from the neighbouring coasts of Epirus, 

 is found (as I have had opportunities of ascertaining) in the sandstone 

 formation, which alternates with the magnesian limestone*. The kind 

 of Tripoli I met with on the Neelgherries, seems to be the result of the 

 disintegration of a species of iron flint found in primitive formations; 

 some of the specimens I collected, have a great resemblance to the 

 Eeisenkeissel of Werner (No. 51). Some varieties of the finest white 

 Tripoli arise from the decomposition of silicious rocks, such as calce- 

 dony, in Corfu and in upper Italy ; but in general, the Neelgherry spe- 

 cimen is not so silicious, and seems to contain a good deal of alumina 

 and iron. It is in this yellow clay that we occasionally see some tubu- 

 lar bodies, formed by concentric layers of the same clay, round the 

 numerous roots of plants that grow on the soil above (No. 6). But 

 what attracted my attention most was, tosee (at Kotagherry) those tubu- 

 lar bodies traversing the thick stratum of black earth, which overlays the 

 yellow clay, without having a particle of it in their composition. As 

 if the roots, by a kind of capillary attraction, sucked up through the 

 black soil, without mixing with it, the particles of the yellow clay 

 which, undisturbed by the vicinity of the black soil, arranged them- 

 selves concentrically to the root \ and the latter decaying has left the 

 cavity of the tube emptyf. 



* It seems to be an argillaceous iron ore, similar probably to the one at Ashburnham, 

 used for the manufacture of Tripoli, and belonging to the Hastings sands. — See Fitton's 

 Geological Sketch of the vicinity of Hastings, page 50. 



t " Brongntakt alludes to something similar to these tubular bodies, enclosing the 

 toots of plants in sandy places, where the iron appears to aggregate the sand round the 

 roots ; and he concludes the paragraph by confessing his inability to assign the cause 

 producing it ' et dans ces-ci la cause qui a accumulg l'oxide de fer a Fentour de la racine 

 . . . .est encore difficile a assigner. — Tabl, des Terr, qui composent VEcorce du Globe, page 56. 



My friend Mr. Malcolmson, late Secretary of the Madras Medical Board, writes to me as 

 follows : On the banks of many of the streams in the Deccan, the black soil is seen pene- 

 trated by tubular incrustations, resembling kankar ; they ai'e evidently formed round the 

 roots of plants, the decay of which leaves a cavity which may sometimes be seen to 

 divide and ramify. Some of those in the banks of the Kanar river, Kamptee, near Nag- 

 pore, are more than an inch in diameter. 



Mr. Prinsep states that " Sergeant Dean's Jumna collection exhibits many incrusta- 

 tions of calcarious and ochreous matter of a similar nature."— See Journal of the Asiatic 

 Society of Bengal, vol. 4, p, 508. 



