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We thank Richard Waitt for his interesting Comment (2007). Though his views clearly do not reflect our own, published discussion is a valuable contribution to the evaluation of any newly suggested terminological scheme. Although Waitt may disagree with our assertion (2006, p. 678) that “genetic connotations also attach to terms derived from sedimentary geology, such as ‘mudstone,’ ‘sandstone,’ and ‘conglomerate,’” we remain of the view that such terms do have genetic connotations for most geologists. One indication of this is that Waitt's own publications stand virtually alone in describing deposits of clear primary volcanic origin (as defined in White and Houghton, 2006) as sediments, whereas thousands of publications treat granulometrically equivalent primary volcaniclastic deposits with one or another volcaniclastic terminological scheme. We tested this assertion by contrasting an “eruption AND ash” keyword search on the Web of Science with an “eruption AND (sand NOT ash)” search on the same site. The former returned 74 hits for papers published in 2006, while the latter only generated 6 hits, and none of those addressed primary deposits.

Waitt's claim that neither grain shape nor origin play a role in the naming of clastic rocks, other than when volcanologists mistakenly use them to name volcaniclastic rocks, is hard to accept given the widespread use of terms such as breccia, talus, etc. Even Folk's useful laboratory textbook (1964–1980), which provides a detailed size classification table for siliciclastic sediments, presents a completely different set of names, divided into different size classes, for clastic carbonate sediment. (The 1980 version is now online at

It seems clear that the Udden-Wentworth (1914, 1922, respectively) scheme is not as universal and non-genetic in application to particulate deposits as Waitt suggests. Researchers in various fields have found reason to employ specific terminological schemes, and this practice is likely to continue because of its utility. Richard Fisher's quote, cited by Waitt, about primary volcaniclastic particles being volcanic on the way up and sedimentary on the way down, sums up Fisher's perceptive approach to interpretating volcaniclastic deposits. Fisher did not, however, describe the volcaniclastic deposits he worked with as sand, sandstones, and conglomerates, but rather as ash, tuffs, and lapilli tuffs. Nor did Fisher do this by “accident” as suggested by Waitt; Fisher, in fact, argued the case for volcaniclastic terms at length in articles and books spanning more than 30 years (see Fisher and Smith, 1991, and citations therein).

Incidentally, there is a scheme universally acceptable throughout science for describing particulate material and deposits, and it has the additional advantage of being precise to any level desired. It is understood by scientists across all fields, and truly lacks any connotations whatsoever regarding particle shape or origin. It is the metric system, not the Udden-Wentworth scale.