In general the coarseness of sand may be determined by different methods in which size distribution (cumulative) curves are used. To obtain such curves, an elaborate mechanical analysis of the sand material is needed. It is shown in this article how the coarseness of sand at different sections of a river may be quickly, though approximately, defined by a single numerical value, without recourse to cumulative curves. Illustrated is a particular case of the bed of the Thames River, in New London, Conn. Some field observations on the compactness of river sand deposits are included in the article.