1836.] 



between Madras and the Neilgherries. 



13 



Seringapatam. — As we remained but a few hours at Seringapatam, 

 my geological observations of that place were very cursory ; therefore 

 what I am going to say of its geological features, is the result of the 

 desultory examination of a very confined spot The localities I visit- 

 ed were the ditch which surrounds the Fort, and the bed of the 

 Cavery. 



On entering the Fort by the southern gate, and descending in the 

 dry ditch below the bridge, I remarked the following appearances. 

 The walls of the ditch show a stratified rock in a decomposed state ; 

 it is gneiss, abounding with mica, which forms, often exclusively, entire 

 strata, as is the case at Baitmungalum, Bangalore, &c. (No. 44). 



Proceeding west along the ditch, towards the Mysore gate, we meet 

 with thick beds of a silicious slate, traversing the gneiss at different 

 places and in all directions. It is probably what Buchanan calls 

 hornstone as found about this place, and in the island of Seringapatam, 

 called by the natives madi-culla ( a.) No. 45. 



The strata of this silicious slate have many feet thickness, and are 

 traversed in all directions by numerous, almost imperceptible, fissures, 

 in the direction of which the rock, when struck, often splits, showing 

 on both surfaces of the separation beautiful, superficial, dendritical 

 appearances, like those occasionally seen in the alpine limestone, and 

 in some novaculites (hones) of the clay-slate formation, produced by 

 the infiltration, through the fissure, of the oxide of manganese, at least 

 as far as it regards the limestone. 



This silicious schist, besides intersecting, as veins, the gneiss, over- 

 lays it in some places, as is seen, on entering the Fort by the Mysore 

 gate, to the right, where it lays in large tabular masses over the gneiss. 



A little farther on, going always west, we see masses of hornblende 

 rock , overlaying the two rocks just described. This green-stone, both 

 as blocks and as dykes, I had seen soon after descending into the ditch 

 below the bridge (No. 46). 



This hornblende rock hardly contains any felspar, and it is evidently 

 unstratified — sonorous when struck — of glimmering fracture — and of a 

 black colour. The elegant columns of Hyder's and Tippoo's Mausoleum, 

 beyond Shahar Ganjam in the Island, are of this rock, which however 

 was brought from a different place, as Buchanan informs us, viz. from 

 Cuddahully near Turivicary, about 52 miles from, and N.E. of, Seringa- 

 patam, and called by the natives Carriculluy or black stone (bj. 



Some of the masses of this hornblende rock have a variolated sur- 

 face, which, however, on breaking the stone, does not seem, to extend 

 into the interior of the rock. I say seem, because, polishing on the 



(a) Buchanan's Journey, vol I. page 133. 



(b) Ibid, vol. II. page 61. 



