Picture a cliff that has been cut open. Bands of rock lie one on top of another, each one its own layer, with clean lines between them. Stratification can be thought of as that picture itself: the making of layers, and the pattern of layers you are left with. Wherever the word turns up — rock, a forest, a society, a set of data — the speaker usually has that stack of bands in mind.
The word is built from stratum, meaning a layer, plus -ification, the making of something. The word itself says: the making of layers.
這個字是 stratum（一層）加上 -ification（形成…的過程）組起來的。字面意思就是「把東西弄成一層一層」，和上面那張圖剛好對上。
Wiktionary entry for stratification, supplied in this packet (source_ref kaikki:3f6f69a190036ae4:438739568:16570): From stratum + -ification.
From the picture
社會被分成上下層
把岩層的畫面套到人身上：社會也被看成一層一層，錢和權力多的在上面，機會少的在下面，中間不容易跨過去。這是一個幫助理解的比喻連結，不是在說這個意思在歷史上比較晚出現。
noun · C1
The way a whole society is divided into separate layers, so that some groups of people have more money, power or respect than others, and moving from one layer to another is hard.
社會階層化
園藝：種子的低溫處理
這一支離「層」的畫面比較遠，是園藝裡的專門說法：把種子放在濕冷的地方一段時間，讓它以為冬天過了，之後才會發芽。本包沒有提供詞源證據說明它怎麼從「層」接過來，所以這裡只把它當成一個獨立的專業用法記著。
noun · C2
In gardening: the treatment of seeds by keeping them cold and damp for a period, so that they act as if a winter has passed and will then sprout.
（種子）低溫催芽
noun · C1
The way earth, sand, rock and similar material settles into layers over a long time, and the pattern of layers that this leaves behind.
層理／成層作用
noun · C2
The dividing of something into separate layers, levels or bands that can each be looked at on its own — used of a forest, a piece of music, a set of data, and other things sorted into strata.
分層／分成層次