《徐霞客游记·江右游日记五》
再往西，峡谷顶上有一块石头将坠未坠，两边的崖壁并排耸起，上下崖石并立，如同从中间破裂而分开的一样，叫一线天。
再西，一石欲坠未坠，两峡并起，上下离立，若中剖而分者，曰一线天。
Further west, on top of the canyon, there is a piece of rock that is on the verge of falling but has not yet fallen. The cliffs on both sides rise side by side, and the upper and lower cliffs stand side by side, as if they had been broken and separated from the middle. This is called Yixiantian.