To lie on top of something, covering it. This is a written word, not a spoken one, and you meet it in two places above all. In geology it is the everyday term for rock layers: sandstone overlies the granite, meaning the sandstone sits above it. In medicine and in old law reports it has a much darker use — a sleeping mother or nurse rolling onto a baby in the night and smothering it; that is what "overlaying a child" meant in old records, and the word still appears in writing about infant deaths. Outside those two worlds, ordinary people say "lie on top of" or "cover". Two things make it awkward to use. Its forms are irregular and easy to get wrong: overlie, overlies, overlay (past), overlain (past participle), overlying. And there is a separate verb "overlay" (overlay, overlaid, overlaid), which means to PUT one thing on top of another — so the past tense of one is the plain form of the other. Even careful writers mix them up.

覆蓋在……之上、位於……上層（地質學常用：上覆）