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Why did Adam Sedgwick and Roderick Murchison disagree about rock boundaries in Wales?

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Ordovician paleogeography — Ordovician Period The distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the Ordovician Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.

The disagreement between Adam Sedgwick and Roderick Murchison arose because they mapped the rock successions of Wales from opposite directions and eventually expanded their respective systems until they overlapped.1

In 1835, Sedgwick named the Cambrian System while working from northwest to southeast, while Murchison simultaneously named the Silurian System while working in the opposite direction. As both geologists continued their field studies, their defined systems began to cover the same geological intervals, triggering a bitter scientific feud over the priority of discovery and the placement of the boundary between their systems.123

This controversy persisted long after the deaths of both men. It was not resolved until 1879, when Charles Lapworth proposed the Ordovician System to define the disputed interval that had been claimed by both the Cambrian and Silurian systems.21