- GeoRef, Copyright 2004, American Geological Institute. Reference includes data from Bibliography and Index of North American Geology, U. S. Geological Survey, Reston, VA, United States
Various properties of glass shards that can be determined in thin sections of volcanic sedimentary rocks of Tertiary age have been tabulated to learn their value in stratigraphic studies and also in stratigraphic correlation. Certain characteristics such as index with respect to balsam, alteration, abrasion, and color do not appear to be useful in stratigraphic correlation. Variation in the shape of shards may be valuable in distinguishing certain ash falls. An ash fall of late Miocene (Barstovian) age of considerable extent was noted to have shards with a distinctive needle-like shape.