ORIGIN OF THE TERRACES. 
103 
surface of contact of the gravels on the Narin clays. Tlic river is now so rapid 
that it washes along heav>' cobbles. A much gentler current is suggested by the 
silts that cap the gravel bluff. 
As the Alabuga is followed eastward, a graded plain makes its appearance 300 
or 400 feet above the terraces just mentioned. It is this higher plain which consti- 
tutes the peneplain, woni on the disturbed Narin fonnation. Bad-land residuals, 
100 or 200 feet in height, still sunnount it here and there ; yet in the district where 
the road crossed over its remnant spurs, the peneplain must have occupied nine- 
tentlis of the basin floor south of the river before the present valleys were cut below 
it. The peneplain here is cloaked with from 30 to 50 feet of gravel, which lies 
unconfonnably on the beveled surface of the tilted clays. At some points a heavier 
brown conglomerate is locally developed at the base of the gravels, as if it were the 
channel fillings of a river. Its outcrops are rather strong, and large blocks from 
it creep down the clay slopes beneath. 
Near the junction of the Alabuga and the Narin, the lower terraces seemed to 
involve successive alternations from erosion to deposition, as indicated in fig. 71. 
A wide, open valley, car\-ed in the tilted 
Narin clays, was filled to a depth of 
more than 150 feet with silts. A smaller 
valley was eroded in the silts, then partly 
filled with a deposit of gravels. The 
present ri\-er plain is eroded about 30 
feet below the gravel plain. The Narin, 
flowing northwestward, soon enters a 
narrow gorge that is cut through a sag 
in the mountains between the Chaar Tash and the Dongus-tau ranges. The red 
basal beds of the Narin formation were seen in the gorge. 
Our road followed up the south side of the Narin, where terraces continued 
similar to those already described. When we camped on its banks for the night, 
clear, cool water was found at the stream's edge, issuing from the gra\-els of the 
terrace to mingle with the turbid current of the river. The river was said by the 
Kirghiz to have a daily fluctuation of level, and to be lowest at about 10 o'clock 
in the morning ; hence that time was chosen for fording it the next day, July 7. It 
was then about a foot lower than when we came to it the evening before. 
The terraces of the Juvan-arik have already been mentioned. The Ula-khol, 
a small river entering the southwestern part of Issik Kul, has several terraces eroded 
in tilted conglomerates a few miles from the lake. 
Fig. 71 
-Three-mile section of Terraces at the junction of the 
Alabuga and Narin f^ers, looking east. 
ORIGIN OF THE TERR.\CES. 
Many more examples of terraces are described in Mr. Huntington's report, 
where strong reasons are given for ascribing the terracing of the valleys in the 
Tian Shan to climatic changes. It may be here pointed out that none of the 
terraces described in the preceding paragraphs resemble the terraces of New England 
in depending on ledges of resistant rock for their protection. If a Narin terrace 
