《徐霞客游记·粤西游日记十一》
一里，抵达屏风山的东北面，立即有个洞斜斜地高张着，洞口朝向东北，洞内往南下倾，渐渐进去渐渐暗下来，大体上与黑洞虽然一南一北方向不同，高低位置相异，可弯弯绕绕地进去，没有不同之处。
一里，抵屏之东北，即有洞斜骞，门东北向，其内南下，渐入渐暗，盖与黑洞虽南北异向，高下异位，而湾环而入，无异轨焉。
After a li, we reached the northeast side of the screen mountain. There was a cave slanting high immediately, with the entrance facing northeast. The cave sloped southward, and it gradually became darker as we went in. Although it was different from the black hole in the direction of north and south and different in height and location, there was no difference in winding in.