在蒸汽机时代之前，运河建设达到顶峰时，一位名叫Smith的地质学家通过收集英格兰各地的地层化石，发现了岩石与化石之间的不同故事。他注意到，在较年轻的地层中，尽管岩石类型相似，但化石种类却能清晰地区分开来。一些化石跨越了数百万年，出现在多个地层中，而另一些则只存在于特定的地层内，甚至有的物种在一个特定地层中诞生和灭绝。这些发现表明，化石可以作为地球历史上特定时期的标志性特征。
As he collected fossils from strata throughout England, Smith began to see that the fossils told a different story from the rocks. Particularly in the younger strata, the rocks were often so similar that he had trouble distinguishing the strata, but he never had trouble telling the fossils apart. While rock between two consistent strata might in one place be shale and in another sandstone, the fossils in that shale or sandstone were always the same. Some fossils endured through so many millions of years that they appear in many strata, but others occur only in a few strata, and a few species had their births and extinctions within one particular stratum. Fossils are thus identifying markers for particular periods in Earth's history.
This was before the steam locomotive, and canal building was at its height.
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