Agassiz Vs. Lyell: Authority in the Assessment of the Diluvium-Drift Problem by North American Geologists, with Particular Reference to Edward Hitchcock

Toward the middle of the nineteenth century in North America, as in Europe, the most vexatious problem of physical geology was to explain the widespread occurrence of erratic boulders, polished bedrock with furrows and scratches, and thick surface deposits of unsorted clay, sand, and gravel. By 1870 the problem had been resolved by a general adoption of Agassiz's glacial theory, which effectively accommodated all these varied phenomena. Agassiz had proposed his theory thirty years earlier, and from the beginning it had been well publicized. Why was its adoption so long delayed? An important consideration is the fact that glacialism had to compete with other, established theories. Although by 1840 it was no longer fashionable to ascribe drift deposits to Noah's Flood, diluvialism in various forms still had its supporters. The more serious contender, however, was Lyell's iceberg theory. In North America the debate had a personal dimension in which, however implicitly, the authority of one immensely prestigious scientist was pitted against that of another. During the period when the debate was most intense Lyell made four visits to North America and Agassiz settled here permanently. Both symbolized European leadership in science and were received with extraordinary respect and enthusiasm. Although Agassiz caught the imagination of the public in a way Lyell did not, Lyell, author of the geology textbook "highest in authority in the English language," had the more solid reputation among professional geologists. The high regard for Lyell and a deepening commitment to Lyellian uniformitarianism helped sustain the iceberg theory. This had the effect of delaying a resolution of the drift problem via the glacial theory.