PHYSIOGRAPHIC OBSERVATIONS. I5I 
the stream and forms the beginning of the floor B terraces. These are, at first, 
narrow, sloping terraces on parallel bedded alluvial conglomerate, but broaden as 
they are followed down the valley, at the same time increasing in height above the 
stream at the rate of about 26 feet per verst, and at Gulcha are about 2,000 feet 
above. Floor B has, however, been much dissected, the tributaries having cut 
down on a normal grade to the trunk stream, leaving intervening alluvium-capped 
hills and spurs as portions of the old rock bottom. Its greatest width, of many 
versts in the lower half of the valley, is evidence of prolonged action and meandering 
of the stream to an extent well towards maturity at the B stage. 
Floor C seems to be the last great characteristic in the records of this valley. 
It coincides with floor B on the plain of Ak-Busa-Ga, but, having a steeper grade, 
separates from it a verst or so farther down the valley, soon attains its full height 
above stream, and continues practically parallel with it all the way to Gulcha, 
except for a few short stretches missing in the canyons. This floor is remarkably 
fresh in every respect, and sunnounts the present bed of the stream over a large 
proportion of its course with vertical and often with overhanging walls. The 
larger branch streams have alread}' cut down to the tnink stream on a normal 
grade, but small tributaries still fall from floor C in hanging valleys. 
Long portions of the valley sides between A and B, and between B and C, are 
marked with transitional terraces, and where the valley widens there is a series of 
three, and sometimes more, freshly cut terraces stepping down from floor C to the 
present stream bed. The striking divergence of terraces is seen b}- a glance at 
the profile. The nmning out of the A and B terraces is a characteristic feature 
soon recognized in the valley, and it was from that fact that the block tilt described 
below was first inferred. 
OBSERVATIONS ON THE SOUTHERN BORDER OF THE FERGANA LOWLAND PLAINS. 
About 30 versts down stream from Gulcha the Taldic darya emerges on to the 
lowland plains of Fergana. We made a brief study of the southern border of these 
plains from 20 or 30 versts east of Osh to Jisak, on the railroad, 30 versts northeast 
of Samarkand. Most of this stud)- was from the railroad train, but there was more 
detailed work done in the region of Osh, and obser\'ations made there ])rojected 
on to the similar forms along the rest of the border. It was found that the waste 
from the Alai Mountains, formerly spread in extensive fans on the border of the 
plains, has been tilted up towards the mountains, dissected in its upper portions, 
and buried bj- later waste on its lower portions. It was obsei"ved from a distance 
that, in general, the Alai range foot-hills begin in long flat-topped masses parallel 
with the range and rising abruptly to a considerable height above the plains. 
The stream followed by the route from Langar to Osh crosses tlie critical zone, 
including the dissected waste and the line where it inclines under the later waste. 
The upper part, or that followed between Takka pass and Langar, was found to 
have cut back a narrow channel increasing in depth to about 60 feet at Langar, 
