THE DESERT PLAINS. 55 
the Tejen, and the track elsewhere was relaid sufficiently to allow trains to cross 
the breaks at low speed. An engine that had approached the flooded Tejen too 
closely was seen mired in the softened mud of the plain ; the track had collapsed 
under it. 
THE .\GGRADING RIVERS OF THE PL.\INS. 
The most notable feature of this district was the absence of valleys. The 
rivers have channels in which their waters are usuall}- restrained, but there were no 
valleys in which the river floods were limited. The plains were open to overflow 
as far as flood supply held out. We were told, however, that some distance 
upstream (to the south) the IVIurg-ab has a flood-plain slightly depressed beneath 
the plain. This we interpreted as meaning that the river had there changed its 
habit from aggrading to degrading. On crossing the Amu at Charjui we saw 
a low bluff on the north or right of its course, although on the south the plain is 
not significantly above the river. 
The general absence of valle>s is a natural, indeed an essential, feature of a 
fluviatile plain in process of aggradation by flood deposits. It is peculiarly appro- 
priate to rivers like the Tejen and Murg-ab, which dwindle away and end on the 
plain, so that even- grain of sand and even,- particle of silt must be laid down as 
the water volume lessens and disappears. The absence of \-alleys would, on the 
other hand, be surprising in a lacustrine or a marine plain, for the reason that 
coincidence could hardly be expected between the slope that might be given to such 
a plain when it is laid bare and the slope that is satisfactory- to the graded rivers 
that run across it. It is not, however, as has already been pointed out, always the 
case that fluviatile plains have no valleys eroded beneath their general level. The 
river-made plains of northern India are now commonly somewhat trenched by their 
rivers. Our Great Plains, piedmont to the Rocky Mountains, are likewise in pro- 
cess of dissection b>- their rivers. The plains of Turkestan are therefore somewhat 
exceptional in this respect. As a result we had unfortunately no opportunity of 
seeing sections of the plains in which the structure of the deposits could be examined. 
A well on the Czar's estate at Bairam Ali, a modern \-illage near Old ]\Ier\-, where 
we were most agreeably entertained by the superintendent, Mr. Dubassof, was said 
to have shown nothing but " .sand and loess." The desert and river deposits found 
by borings beneath the Anui River bed at Charjui have already been noted. The 
inspection of these vast plains of silt was very suggestive in connection with the 
problematic origin of the fresh-water Tertiary fonnations of the western United 
States. Certainly no one who sees the river-made area of the plains of Turkestan 
can doubt the capacity of rivers to lay down extensive fine-textured deposits. 
The ruins of old IMer\' are situated on the fluviatile plain, where large canals 
must have once led a plentiful water-supply from the upper Murg-ab. They lie some 
1 2 miles east of the oasis of modem ]\Ier\-, in which the greater part of the river is 
now used for irrigation. It is therefore especially desirable to make careful exam- 
ination of the earliest of the ruins with respect to the level of their foundation and 
its relation to the surface of the surrounding plain. Some of the ruins are only a 
few centuries old ; the cities that they represent are known to history. Others have 
