Cavansham Ferry and Llanstephan Quarries

On the right bank of the River Wye, by Trerickett Mill, the “Old Red Sandstone” (Devonian, Pridoli, Moor Cliffs Formation) is “quit” and “Grauwacke slate” (Silurian, Ludlow, Ludfordian) is exposed in the bed of river, and crops out on the left bank as several “low terrace-shaped ridges”. This is the first site where Murchison encountered “grey-coloured strata” of “grauwacke” containing fossils he considered “differing from any known in superior deposits”. Crossing the river at Cavansham Ferry Murchison “rushed up to those ridges” at Llanstephan Quarries, and to “inexpressible joy found them replete with transition fossils.” Upwards, “the strata…plunges to the east…under the Old Red Sandstone.” The archaic geological descriptions quoted here were used by Murchison in his 1831 field notebook No.2. Later, he noted: “The order of succession seen in the left bank of the Wye…first led me to suspect I had met with a district that contained a good part of evidence required to lead to a systematic study of older formations.” (Murchison 1839, 5). Retrospectively, Murchison considered this site as the location where he discovered the Silurian, culminating in his establishment of the Silurian System. As such, it provides great insight into Murchison’s early fieldwork methods and thinking.