Yet it would be nearly impossible to overstate Lyell's influence. The Principles of Geology went through twelve editions in his lifetime and contained notions that shaped geological thinking far into the twentieth century. Darwin took a first edition with him on the Beagle voyage and wrote afterwards that 'the great merit of the Principles was that it altered the whole tone of one's mind, and therefore that, when seeing a thing never seen by Lyell, one yet saw it partially through his eyes22.' In short, he thought him nearly a god, as did many of his generation. It is a testament to the strength of Lyell's sway that in the 1980s, when geologists had to abandon just a part of his theory to accommodate the impact theory of extinctions, it nearly killed them. But that is another chapter.