PHYSIOGRAPHY OF SOUTHERN SHEN-SI. B35 
valley in Cambro-Ordovician, and it is evident that such stretches were 
originally determined above the Carboniferous on the red beds, whose posi- 
tion would now be between 4,000 and 5,000 feet, 1,200 and 1,500 meters, 
above water. But the various stretches of the river are not even approxi- 
mately axial along synclines, and they alternate with other sections across 
and along anticlines, sections which are not adjusted to structural condi- 
tions. Hence we are led to infer that the present course of the Yang-tzi is 
not one which was taken upon a fluted surface due to folding, but may be 
either a derivative from such an original course or else one which has devel- 
oped by the growth of a smaller but dominant river, that by a succession 
of captures succeeded in uniting many watersheds. The record of such 
derivation or development is not to be seen from the river. The Yang-tzi 
is imprisoned by tremendous canyon walls, which its own flood has carved 
and is still carving. Whatever channel it once had other than that which 
it is deepening, may be traced only above the great cliffs among the moun- 
tain summits. 
In deepening its channel, the Yang-tzi has lowered the level of dis- 
charge of its tributaries, and so has promoted their growth in competition 
with the tributaries of the Han. The divide of the Kiu-lung-shan should 
be the direct resultant, but is not. The Ta-ning-ho has a much shorter 
course and steeper fall than the Nan-kiang, a tributary of the Han, and 
about its headwaters is favored by an area of shale, in which it once 
developed the wide valley of the Ki-sin-ling; nevertheless it has lost that 
valley to the Nan-kiang, a loss which, as we have already noticed, could 
only have been occasioned by strong warping. The axis of maximum 
upwarp appears to lie not far south of the Ki-sin-ling, and the descent from 
it toward the Yang-tzi is apparently one of about 2,000 feet, 600 meters, 
in 50 miles, 80 kilometers. It is on this slope that the Ta-ning-ho and other 
southward flowing tributaries took their course, directly across the struc- 
tural lines of the region. The fact that we do not find any great longi- 
tudinal valleys between the crest of the Kiu-lung-shan and the Yang-tzi 
would seem to indicate that this condition was a general one, and that 
the older drainage, whatever its courses may have been, was completely 
dissected and diverted. 
Where we pass from the I-chang gorge eastward beyond the moun- 
tains, the surface sinks gradually toward the flood-plain of the Yang-tzi and 
the strata dip gently beneath it. The long slope is margined by foothills 
of red beds and higher up corresponds over large areas with the dip plane 
of the Carboniferous limestones. Though sometimes described in terms 
of exaggeration as of wall-like steepness by which a fault-scarp is suggested, 
it is a warped topographic surface, an eastern slope of the broad upwarp 
