Lyell's concept of gradualism and accompanying process observation on an expanded time scale resulted in firmly establishing the fact that much could be accomplished by small forces working constantly for long periods. That conclusion is consistent even with present-day thought. Lyell's almost total rejection of any geologic process that was abrupt and suggestive of catastrophe, however, was in itself an extreme posture. Research has shown that both gradual and rapid changes occur.
In the philosophical climate established by Hutton's uniformitarianism and Lyell's gradualism, geomorphologists of the 19th century realized many impressive accomplishments. Most notable among these were the studies of glacial phenomena in Europe by Johann von Charpentier and Louis Agassiz and the investigations of regional denudation in the American West by Grove K. Gilbert and Clarence E. Dutton, which emphasized the work of running water. The findings pertaining to glaciers still stand for the most part, and Gilbert's hydraulic studies laid the groundwork for modern ideas. Yet, neither he nor Dutton made comprehensive theoretical proposals of terrestrial morphogenesis of a scope that could match those of the aforementioned W.M. Davis.
Excerpt from the Encyclopedia Britannica without permission.