OASES. SOL 
tributary canal, they built their citadel, piling it up with clods of clay to a height of 
34 feet, and around it threw up the massive walls of the inner city, of whose colossal 
height more than 70 feet still remains. That the outer city with its walls was 
laid out at the same time we have shown to be likely. So they built their city 
and from that time the distributary stream they had chosen is for physiographic 
purposes to be regarded as an irrigation canal, and the sediments laid down upon 
its flood-plain, irrigation and canal sediments, according to whether the area 
considered was under cultivation or not. While the débris of occupation rose 
within, these sediments grew upon the plain without the walls and to a certain 
extent continued growing after the abandonment of Ghiaur Kala in the eleventh 
century; for it was then that a new Merv, whose ruins are now called Sultan 
Sanjar, was founded but a few hundred yards away and water still found its 
way into this region. 
Loess, dune-sand, alluvium, and human débris is, therefore, the stratigraphic 
order of our physiography at Merv, the record of Nature and man, the effect for 
which we seek a cause. And of all time-sections it has been our fortune to study, 
this one is the most beautiful illustration of the organic changes that constitute 
the process of a great interior desert region effected by climatic change. 
During the accumulation of loess there must have been a sufficient precipi- 
tation to nourish grass over this area, but it is now too arid. It was then doubtless 
a time of greater precipitation over the Murg-ab’s catch-basin which would enable 
that river to penetrate farther into the desert giving it a delta north of the present. 
The flying sands derived from wind-work over the delta were probably accumu- 
lated into more or less stationary dunes around it, while most of the finer material 
settled as loess between it and the mountains. Then, I believe, a decrease in 
precipitation demolished the grass, set free the dunes to drift over all neighboring 
areas free from alluviation, while the river shrank with its delta, receding moun- 
tainwards to build over the dune-strown loess topography of Ghiaur Kala, and 
at this stage the city was founded. 
