:27s 
Jicconls of the Geological Surreg of Lidia. 
[ V(),r,. XTir. 
bulged appcai’nnce of tlic lull, whicli makes tlic slope steeper near the bottom 
than it is liiglier up, being occasionally, as above the mission premises, as steep 
as 35°. 
These two areas can bo recognised on the map; the even slope near the 
lower end of the lake is drained hy innumerable channels running almost straight 
down the hill, while on the bulged portion the streams are fewer and their 
courses not nearly so directly down the hill. 
The cause of tliis bulged appearance I take to bo as follows : By the action 
of the weather the face of the hill gets covered with a greater or less thickness of 
decomposed rook, which, as already explained, weathers into a mass of small 
fragments. The rain water, which obtains access to the interior of the hill, for the 
most part keeps in this decomposed layer and flows down at a short distance from 
the surface, passing out again lower down in the springs which exist in numbers 
over this hill, and a large part doubtless piercolating do^vnwards reaches the lake 
without coming to the surface. The presence of large quantities of water among 
this decomposed rock must, hy making it more mobile, assist in prodiicing that 
|)honomenon wdiich is seen in any mass of debris lying at a slope, Avhother it be 
^vet or diy, namely, the gradual passage of such debris down the slope under the 
influence of gravity; that some movement of the debri.s down the slope takes 
jilace after heavy rains, seems certain, as is shown by cracks appearing in the 
surface of the hill side, the lower .side of which subsides slightly. Now on a 
level surface the action of gi-avity can have no effect in producing any motion, 
wliilc on a slope the force tending to produce such motion varies directly as the 
resultant of the vertical force of gravity acting directly down the slope, that is, it 
varies as the sine of the angle of inclination. Suppose, then, an even slope 
passing near its base into level ground, and that slope covered with debris ; the 
debris slides slowly down the hill, but on the steeper parts of the slope it must do 
so faster than near the bottom, where the .slope is less and there is the I’osistance 
of the debris lying on the level to be overcome, ■which can only bo done by a vh 
a t&rijo, an impulse from behind. The debris coming skmly do'wn from above 
and meeting with this obstacle gradually accumulates till it causes a bulging of 
the slope towards its base, which goes on increasing till the lower part of the 
hill is so steep that, to use a colloquial 25hrase, “ it is touch and go” whether 
the hill can stand or not; then a burst of rain heavier than usual comes, 
the head of water is increased, the force of the water flowing out near the 
bottom is increased, it begins to wash away the debris near the bottom till 
the support being removed from below small slips begin to fall; then a few 
larger, and finally comes the great slij), ■which brings down the outer crust 
of half the hill side, leaving a preciijitons border round that part from which it 
has come; finally, the great slijj is followed by smaller ones, which leave the hill 
with a ju'etty uniform slope from top to bottom for the whole process to begin 
again. Such I believe to bo the liistory of one of these landslijis where there is 
no stream cutting at the base of the hill; where that is the case, slips may be 
formed at any time by the cutting away of the foot of the slojje. 
The slqj under consider,ation has followed very much the course pointed out; 
the. bulging had reached the critical i^oint : all through last rains small slqjs 
