.1833.] ‘Second Report on the Geology of Hyderabad. 895 
‘the banks or sides of the mountain being so steep as even to preclude 
communication in any other mode than by water. ; 
The extent of the modern inundation varies from six to three 
miles on each side of the river, but judging from the distance at which 
the black alluvium is found from the banks of the river, these periodical 
floods have been more extensive*. 
The last took place in the year 1816, and washed away houses and 
cattle in great numbers; and there are traditions of two others in the 
course of the last, century, each greater than the last. Iam _ not able 
to speak with so much certainty of the inundations of the Kiséna ; 
I have however seen the black alluvium covering the plain in 
which the diamond mines of Purted/ are situated, extending six miles 
from its banks; also at Shermahomedpet, five miles N. W. of its 
bank. 
These inundations are considered as important benefits by the inha- 
bitants, and the produce of the land is proportionally increased after 
their occurrence. 
Tanks. 
The lakes I have seen are all artificial, and are found only in the 
granitic and sandstone country ; they are usually formed by uniting two 
projecting points of low hills, which nearly separate the upper half of a 
valley from the lower, by enormous causeways of granite, or mounds 
of earth, which collect the different streams rushing from the‘hills 
_during the rainy season, forming a sheet of water from three to ten miles 
in circumference. 
This mode of retaining water artificially is probably coeval with the 
first increase of population in this country, as the small supply of water 
derived from wells would not be equal to the cultivation of rice, which 
-is the only grain extensively produced in the granitic soil. 
After the rains the loss they sustain from irrigation, evaporation, &¢. 
is supplied by infiltration, nevertheless many become dry before the 
‘monsoon recommences. Those tanks which are neglected and no 
longer supply rice-fields are speedily covered with the large leaves and 
flowers of the nelumbo indica, othelia alismoides, and other aquatic plants’: 
their waters acquire a noisome smell and unwholesome taste. The num- 
ber of tanks and their state of repair afford a fair criterion of the aa 
perity of the country. — 
* From subsequent observations, I am inclined to believe that this alluvium or 
diluvium was the result of a deluge of water which found its course to the sea by 
the present opening of the rivers—and that they have done no more than form 
their beds in it. 
i 
25 2 
