Scrope, George Poulett (1797-1876). Memoir on the geology of central France; including the volcanic formations of Auvergne, the Velay, and the Vivarais. London: Printed for Longman, Rees, Orme, Brown, and Green, 1827
The man who really discovered geological time through the study of volcanoes was George Poulett Scrope. He spent a year in the Auvergne, Velay, and Vivarais regions of south-central France, tracing extinct lava flows. He found an extinct volcano near the city of Jaujac in the Vivarais, where there was evidence that lava had streamed from the crater and completely filled the valley of the Alignon river. Then a river had excavated more than 200 feet of the deposit, revealing vast cliffs of columnar basalt. In other places he found layers upon layers of basalt, eroded by water, and then filled up again by subsequent eruptions. All of this must have taken an immense amounts of time.
Scropes illustrations of central France were elaborate multiple-folding plates that were very expensive to print, and so publication was delayed for more than five years. The plate shows the Jaujac region, and the text volume is open to the page where Scope concludes with his famous remark, that the leading idea present in all his researches is this: "Time!-Time!-Time!".