from The standard geologic column--
Roderick Impey Murchison, born 1792 (died on this day in 1871, discoverer of the Silurian & Permian layers)
"began his study of the Transition at the unconformity and worked his way down through its strata unfolding these and ordering them as he went. He paid much attention to the fossils in the strata and used them to correlate the strata between exposures. The system he described he named the Silurian (for a tribe, the Siluries, that had inhabited the area at the time of the Roman conquest). In 1839, he published in his first monumental account of the Silurian System. Murchison was knighted in 1846 for his geological contributions and was unstoppable in his adding ever older layers of the Transition rock to his Silurian System. These he announced in successive editions of his work Siluria (5th ed. 1872). His efforts came to intrude upon the work that Sedgwick had taken upon himself which was to work upward from the base of the Transition formation. Adam Sedgwick (1785-1873) began his study of the Transition in the most mountainous part of Wales, which is its north and where, from Wernerian reasoning he would surely find the oldest strata in contact with the Primitive. He would work his way up through the Transition strata. The first formation he mapped in detail he called the Bala Limestone. In the company of Murchison, he noted that the fossils in these were similar to those of the Caradoc Sandstone Formation in Murchison's field area. However, Murchison used Lyell statistical method to assign age by fossil content, and the more contorted limestone and slaty nature of the graywacke rocks in Sedgwick's area decided them (by Wernerian reasoning) that these were of different age. The rocks in Sedgwick's field area were not very fossiliferous. To order the strata he relied mostly on lithology and the "strike" (from the German Streichen and which tells of Elie de Beaumont's influence) of units to correlate between nearby exposures. Use of the principle of superposition to order strata was made difficult by their folding (he coined the word synclinorium for an area of folds in which younger strata are exposed centrally). Acrimony arose when Murchison changed his mind and made the Caradoc and Bala age correlatives and then proceeded to add layers below to his Silurian system. in the faunas. However, in 1852, Sedgwick's paleontological assistant established a clear difference between the faunas in the upper and lower beds of the Carodoc. Also, careful regional mapping found that a angular unconformity (hard to see locally as all is folded) divides the Carodoc and the Bala Limestone Formation. This break in the rock record became the recognized bottom boundary of Silurian in Wales when, in 1879, Lapworth formally proposed the name Ordovician for the time represented locally by the Lower Bala and Carodoc Formations including a few of the strata in contact below. The name Devonian derives from a Romano-British tribe that once lived in the Bala District of North Wales. Beneath the Devonian is a slaty formation called the Lingula Flags and below this graywackes that contain the distinctive trilobite Paradoxides. These were part of the sequence that Murchison had originally included in his Cambrian (derived from the Latin name for Wales). And so they are called, which posthumously settles the squabbles of the erstwhile friends."
