PHYSIOGRAPHY OF SOUTHERN SHEN-SI. 339 
there is between the gorges of the Yang-tzi and those of the Hu-t’o-ho in 
similar limestone no such difference of development as would justify us in 
assigning to the one feature or the other a notably longer existence. With- 
out committing ourselves as to the relative age of one local uplift or another, 
we may say, with confidence, that the great ranges of Chi-li, Shan-si, and 
Shen-si all belong to a common time of mountain growth. The epochs 
which preceded them are, in North China, the Hin-chéu and the preceding 
T’ang-hién, and in Central China the Ts’in-ling. The last named covers 
the Hin-ch6u and extends back into T’ang-hién time, in all probability; 
but inasmuch as the features of the Ts’in-ling surface are less mature than 
those of the T’ang-hién, it is not probable that the two overlapped during 
any great part of their history, provided the rates of erosion in the two 
districts have been even approximately the same. The Ts’in-ling epoch 
was initiated by warping apparently when the T’ang-hién was well advanced, 
and in Central China degradation has since been continuous, while in parts 
of North China it was interrupted during the Hin-chdéu epoch. 
Thus, stating the relations of the epochs in the order of development 
we nay say: The Tss’in-ling stage of Central China corresponds in duration 
with the later part of the T’ang-hién and the entire Hin-chéu epoch of 
North China; the Yang-tzi and Fén-ho stages have been essentially con- 
temporaneous. 
By reference to the discussion of geologic dates of the several stages 
of physiographic history of Northwestern China at the end of Chapter XI, 
it will be seen that the correlation reached in the last paragraph places 
the Ts’in-ling stage in the late Tertiary and the Yang-tzi epoch chiefly 
in the Quaternary. 
