SERINGAPATAM— THE DITCH OF ITS FORTRESS EXAMINED. 
307 
from the parent rock, and the lamina is ea- 
sily removed, and cut in as many pieces as 
required. 
The curvature of these laminae being the 
segment of a very large circle, in the small 
dimensions they are generally cut, they ap- 
pear nearly straight, and are used for all 
architectural imrposes, as columns, door- 
posts, steps, &c. 
I have read, I do not recollect where, that 
the foregoing process is had recourse to, at 
Bangalore, to split granite. This must be a 
mis-statement, since at Bangalore, as well 
as in many other places in India, they use 
another, and very different, method to split 
granite, porphyry, green-stone, or other 
unstratified rocks.” 
Dr. Benza does not recollect to have 
ever seen in India the gneiss so well 
characterized and its strata so much con- 
torted as in this locality. The whole, 
mass of this gneiss has the usual convex 
surface ; and exfoliates in thicklaminse, por- 
tions of which lay, like huge cubic pieces, on 
the convexity of the rocks. Our author pro- 
ceeds next to Chinnapatam, a village situa- 
ted in a plain. Hornblende slate is the rock 
jutting above the soil near Kingairee and 
Closepet. Here he found pieces of rock 
which he was inclined to call porphyry ; they 
were unstratified,- composed of semi-foliat- 
ed felspar, approaching to compact, and glit- 
tering — penetrated by numerous microscopic 
cavities, occasionally filled with a yellow 
clay, and containing grains of perfectly 
transparent white quartz, some of them 
in regular crystals of that mineral. 
Dr. Benza reaches Mundium, between 
which and Chinnapatam the rocks are 
hornblende-slate, intersected in all di- 
rections by numerous quartz veins, of 
divers dimensions and shapes. In its vici- 
nity our author picked up some loose pieces 
of talcslate, mica-slate, &c. He now proceeds 
to Seringapatam where he only remained a 
few hours : he visited the ditch which sur- 
rounds the fort, and the bed of the Cavery. 
the walls of the ditch showed a stratified 
rock of gneiss, abounding with mica, in a 
decomposed state ; he met v>fith thick beds 
of silicious slate, traversing the gneiss 
at different places and in all directions, 
and supposes it to be what Buchanan calls 
hornstone, called by the natives madi-culla. 
The strata of this silicious slate have a 
thickness of many feet, 
“ And are traversed in all directions by 
numerous, almost imperceptible, fissures, in 
the direction of which the rock, when stiuick, 
often splits, showing on both surfaces of the 
separation Ireautiful, 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, overlays 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. 
This hornblende rock hardly contains any 
felspar, and it is evidently unstratified — so- 
norous 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 Turivieary, about 52 
miles from, and N. E. of, Seringapatam, 
and called by the natives Carricullu, or black 
stone. 
Some of the masses of this hornblende 
rock have a variolated surface, w'hich, how- 
ever, on breaking the stone, does not seem 
to extend into the interior of the rock. 1 say 
seem, because, polishing on the stone, the 
rounded marks re-appear and of a deeper 
colour than that of the rock itself. 
Buchanan took particular notice of these 
darker spots in the polished rock, and at- 
tributed them to the crystals of basaltine 
(so was augite called at the time he wrote) 
imbedded in the hornblende ; in Avhich con- 
jecture I think him perfectly correct, as the 
mineral is augite which gives the described 
appearance to the rock, and it is seen clearly 
marked in the above mentioned columns of 
Hyder’s Mausoleum. 
It must be remarked that the veins of the 
silicious schist, intersecting the gneiss up to 
its surface, do not penetrate into the over- 
lying green stone, showung the posterio- 
rity in age of the last mentioned rock. 
In going out of the Fort through the 
northern sallyport, close to which Tippoo 
wms killed, you come upon the right bank of 
the Cavery, which washes the walls of the 
Fort at this place. When I visited Seringa- 
patam (March 1834) there being very little 
water in the river, ail the rocks forming its 
beds w^ei*e exposed to view, enabling me to 
judge of their nature. 
The principal rock in it is gneiss, which 
appears to extend along the course of this 
river for a considerable distance ; since I 
have met w ith the same rock, jutting abov« 
