与此同时，地质学有大量的分类工作要做，这项工作不是什么都一帆风顺的。从一开始，地质学家就想把岩石按其形成的时期来进行分类，但在怎么划分时期的问题上经常发生激烈的争论——而且是一场旷日持久的争论，后来被称之为“泥盆纪大争论”。剑桥大学的亚当·塞奇威克断言有一层岩石是寒武纪的，而罗德里克·默奇森认为它完全属于志留纪，争论于是就发生了。争论持续了好多年，而且越来越激烈。“巴谢是个下流痞子。”默奇森在给一位朋友的信中气呼呼地说。

Some sense of the strength of feeling can be gained by glancing through the chapter titles of Martin J. S. Rudwick's excellent and somber account of the issue, The Great Devonian Controversy. These begin innocuously enough with headings such as "Arenas of Gentlemanly Debate" and "Unraveling the Greywacke," but then proceed on to "The Greywacke Defended and Attacked," "Reproofs and Recriminations," "The Spread of Ugly Rumors," "Weaver Recants His Heresy," "Putting a Provincial in His Place," and (in case there was any doubt that this was war) "Murchison Opens the Rhineland Campaign." The fight was finally settled in 1879 with the simple expedient of coming up with a new period, the Ordovician, to be inserted between the two.

在《泥盆纪大争论》一书里，马丁·J.S.鲁迪克极好而又有些沮丧地描述了这场争论。只要瞥一眼该书各章的标题，就可以知道一点上述感情的强烈程度。开头几章的标题的语气倒还温和，比如《绅士们的辩论舞台》和《破译杂砂岩之谜》，但接着就是《捍卫杂砂岩与攻击杂砂岩》、《指摘与反驳》、《散布恶毒的谣言》、《韦弗撤回邪说》、《杀杀乡下人的气焰》（惟恐你还怀疑这不是一场战争）、《默奇森发起莱茵兰战役》等等。争论于1879年得以解决，办法很简单，在寒武纪和志留纪中间加一个时期：奥陶纪。