GEOGRAPHICAL SUMMARY 
183 
areas. On the north it is bounded by the Alai Mountains, 
on the east by the chain of Sarik-kol, on the south by 
the Hindu-kush, whilst its western limit is marked by 
the line of 73° E. long. According to Von Richthofen, 
the definitive characteristic of a region belonging to the 
Transitional zone is the fact, that the erosive power of the 
water, and the resultant action of the violent alternations 
of temperature, have in more recent times broken a new 
path for the drainage streams, so that instead of seeking 
an interior, land-locked basin, they are now able to find an 
outlet to the rivers which eventually discharge into the sea, 
or vice versa, they cease to send their waters oceanwards, 
but turn them instead towards an interior basin which 
makes no contribution to the seas around the continent. 
A Transitional region is therefore one which retains the 
typical features of the region to which originally it de- 
finitively belonged. 
The Transitional zones of the Pamirs bear a very close 
general resemblance to the self-contained drainage-basin of 
the Kara-kul. Erosion is not yet sufficiently far advanced 
to enable the streams to carry off all the products of dis- 
integration which cumber the valleys, the contours are soft 
and rounded, the valleys themselves broad and shallow. 
The tendency of the active disintegrating forces operative 
in the Pamirs is to convert it into a Peripheral region. 
For instance, in the south - west the little brook of 
Kok-uy-bel, a feeder of the Murghab, which in its turn 
goes to augment Lake Aral, has extended its remotest 
arteries to within about six miles of the brook of Mus-kol, 
which discharges into Lake Kara-kul. The springs which 
give origin to the Kok-uy-bel lie only a trifle higher than 
the level of the lake ; so that, geologically speaking, the 
Kok-uy-bel may perhaps to-morrow be converted into 
an outlet from the lake, through which its waters wou 
gradually flow away till it became empty. Simultaneously 
with this change, the Kara-kul depression would begin 
to lose the characteristic features of an indepen ent area 
of internal drainage, and would gradually assume those o 
a Peripheral region. 
