The North Shen-si Basin is a great oval sedimentary trough (figure 1) measuring about 450 miles from north to south and 250 miles from east to west, lying chiefly in northern Shen-si, but extending into Mongolia, Shan-si, and Kan-su. Its area is approximately 100,000 square miles.
The great northern loop of the Hwang-ho roughly marks the northern limits of the basin; the high mountains of western Shan-si bound it on the east; the southern rim is not far north of the fault-front of the Ta-hua and Tsin-ling mountain ranges, extending westward across Shen-si from the acute bend of the Hwang-ho at the southwest corner of Shan-si, while the broken north-south mountains of east-central Kan-su border it on the west.
The northern third of the basin lies within the sandy or gravelly deserts of the Ordos, while the southern two-thirds, separated from the northern section by a . . .