238 THE BASIN OF EASTERN PERSIA AND SISTAN. 
(pp. 133-134) speaks of the "soft-sided" hills as being worn away so fast that "the 
mountains ran down to the plains in rivulets of mud." Because of this rapid process 
of degradation the mountains north of Herat "are certainly not such as were 
described by classical writers two thousand years ago." The wonderful rapidity of 
erosion is illustrated b>- a stoiy related by Holdich (p. 135) of a place in this region 
where the hilltops consisted of a stratified, somewhat loess-like formation of recent 
date. In descending from the top of a hill during "quite an ordinary hailstorm 
. . . I was up to my knees in a moving mass of liquid mud. ... By 
evening that mud had spread out in a thin but very measurable sheet of surface 
soil far over the plains all around the hill ; and the hill was definitely smaller and 
the plains definitely higher than they had been the day previous." It is possible 
that the region is as }oung in years as Kopet Dagh, although the topography is 
mature by reason of the softness of the strata. 
A section along the Heri Rud from Serakhs southward leads to the same 
conclusion. At first the stream flows in a terraced valley intrenched some 20 or 30 
feet below the alluvial plain which stretches indefinitely northward. Toward the 
south, however, it traverses a region of low hills composed of an alluvial deposit, 
which seems to be of the same character as the plain and as the deposits which are 
now being laid down by the ri\er, although older than either. Where exposed in 
section by the undercutting of the river, as at Nauruzabad, 25 miles south of 
Serakhs, for example, the alluvium consists of fine stratified silt, brown in color, 
l=Cretaceous limestone; 2=Tertiary brown limestone; j^Tertiary brown sandstone; 4=Tertiary 
thin clayey limestone ; 5— Tertiary soft sandstone ; 6= Tertiary impure yellow limestone ; 7=Ter- 
tiary reddish-brown sandstone ; 8= Tertiary white limestone. 
Fig. 154. — North and south section along the Heri Rud at Pul-i-Khalun. 
and, in some layers, with a texture much like typical loess. Overlying this is thick 
gravel, and interstratified with it are bands of gravel lenticular in shape and some- 
times reaching a thickness of 5 or 10 feet. This deposit, formed apparentl}- by 
the ancient Heri Rud, covers most of this corner of Transcaspia from the Afghan 
border northward. Often it is concealed by drifted sand or loess ; sometimes it is 
interrupted by projecting bits of an older sandstone, presumably of Tertiar>' age, 
which dips gently northward where I saw it at Pul-i-Khatuu salt lake. Back from 
the river, east of Pul-i-Khatun (Ladies' Bridge), the soft allu\-ium assumes the form 
of low, rolling hills, well graded and mature, which toward the southeast gradually 
increase to a height ot 4,000 feet. The main valleys are bordered by terraces cut 
for the most part in gravel. 
At Pul-i-Khatun the alluvium comes to an end where the Heri Rud emerges 
from the mountains through a narrow gorge composed of the Tertiar}' strata shown 
in the accompanying section (fig. 154). These strata form a smoothly truncated 
ridge, in which the river has cut a sharp notch. South of this Tertian,- ridge lies 
a great body of calcareous Cretaceous strata forming the main mass of the moun- 
