《论衡·卷十三·效力篇》
至于很大的石头，没有泥沙覆盖，山又不能支撑，处在悬崖峭壁的边上，就必然会崩塌坠落到坑谷里去。
至於大石，沙土不覆，山不能持，处危峭之际，则必崩坠於坑谷之间矣。
As for very large rocks, which are not covered by mud and sand, and which the mountain cannot support, being on the edge of a steep cliff, they will necessarily collapse and fall into the pit valley.