Knowledge Bank

Electron micrographs of sand grains from southern Piedmont saprolites, temperate and polar glacial deposits, and the St. Peter Sandstone are presented. Sand-grain surface features of saprolite grains are described for the first time and from these some concept of the initial surface of a quartz sand grain is obtained. Micrographs of the sand grains from glacial deposits whose erosional history was limited to ice action uniformly show strongly striated surfaces. Comparison of the features described here with those offered as criteria for a glacial history by previous workers suggests the need for further evaluation of the published criteria. Further study should be made of sand-grain surfaces using sands which have been exposed to a single erosional agent to allow for the determination of more rigorously denned criteria for the interpretation of their geologic history.