Stratigraphic Value of Volcanic Ash
Charles R. Keyes · UNI ScholarWorks (University of Northern Iowa) · 1925
Layers of volcanic ash which are commonly looked upon as ordinary clay- or shale-seams between dominant rock strata are often very wide-spread, and pass through different geographic provinces in utter disregard to local sedimental successions. Recent use of these ash-beds in correlation problems indicate that they may prove to be the most precise chronological markers which we have encountered. It is believed now that through the medium of these beds of dust from volcanic eruptions a new stratigraphic regime is at hand, the underlying principles of which, for precision and ease of application in the field, surpass quite as far the epoch-making discovery of William Smith a century ago as did his plan those methods which he displaced.