EXAMPLES OF TERRACES. 
261 
is bounded by steep bluffs, 35 feet high, which on the north and northeast are com- 
posed of a rather solid fonnation which appears to be a portion of the half-lithified 
basin silts of Tertian*- age. On the southeast and south the bluff consists entirely 
of stream-laid gravel. On the northwest side, whence the lake receives its water 
supply, a plain, at first marshy, rises gently to the great basin plain of silt bordered 
by gravel, in which are located Kalagak and Turbat-i-vSlieik Jam. The rise from 
the lake to Kalagak, however, is not perfectly smooth, for beyond the marsh)- border 
it is broken by two small terraces, the lower of which is very slight, while the upper, 
perhaps 15 feet above the water-le\-el, is also slight, although it is clearh- marked. 
Around the lake itself, at the foot of the bluffs and about 10 feet above the water- 
level, is a beach which extends downward 4 or 5 feet. It may represent the extreme 
high-water level of to-da}-, although I could get no information on this point. It 
Fig. 1 58. — Sketch-map of Kogneh Lake and tKe Jam Basin. 
probably corresponds to the lower terrace. The bluff which surrounds the lake is 
very flat-topped and is unbroken except at one point on the southeast side, where 
there is a notch, broadly flat-floored and some 12 or 15 feet deep. This notch opens 
into the head of a well-defined valley which discharges to the Jam River, as shown 
in the sketch. It is evidently not occupied by water even during tlie highest floods, 
and there can be no doubt that it is an abandoned chamiel, representing a former 
higher stand of the lake. It probably corresponds to the upper of the two small 
terraces on the northwest, but the latter seemed to be lower than the notch, and as 
no exact measurements could be taken the matter must be left inisettled. The 
phenomena immediately about the lake indicate that the water must at various times 
have stood at three, or possibly four different le\-els. First, the le\-el of the top of 
