30 Address of Sir R. I. Murchison 
have been diminished, though he is firmly of opinion that such 
a deep depression could not have been emptied and refilled. In 
reference, however, to the former Caspian branch of the Oxus, 
in the existence of which he believes, he supposes that many 
streams, now dry or nearly so, formerly augmented the vol- 
ume of the Oxus, thus enabling it to supply a branch to the 
Caspian by the Gulf of Karabogas, and that to the failure of 
this supply we may attribute the drying up of the branch, 
term them both Ala Kul simply, because they are unac- 
quainted with the marshy and inaccessible isthmus between 
them. In Central Asia, too, the River Tchu, through its de- 
direction are effected in the course of rivers in flat and sandy 
countries is well known to many Russian geographers who 
have explored Central Asia, 
Thus, the Oxus, deprived of many of its former affluents, 
ceased to be able to throw any portion of its waters into the 
Caspian, and took the straight course into the Aral, This 
natural operation, as Semenof observes, may have also been 
subject of the now desiccated. former 
may state, on the authority of my cor- 
Helmersen, that recen : 
memoir was 
Feographical Society of St. Peters- 
