《徐霞客游记·粤西游日记十二》
以为由后洞向西出去，可以返回来登到上洞穿通之处，可后洞上下都如刀削，旁边无处可攀。
以为由后窍西出，可反跻上岩透处，而后窍上下俱削，旁无可攀。
I had thought that if I could go out to the west from the back cave, I could return and climb up to the higher cave's opening but the back cave was cut away like a slice of a knife上下 and there was nowhere to climb.