Lacustrine and fluvial Tertiary sediments of the Uinta Basin, Utah differ markedly in many primary respects, and display features which may be diagnostic of the principal environment in which they were formed. The fluvial and lacustrine sandstones are similar in mass properties, differing primarily in that lacustrine sands are more uniform in appearance than fluvial sands. The lacustrine shales are denser, harder, better bedded, more continuous, somewhat thicker, and contain considerably more of the carbonates, limestone and dolomite, than the fluvial shales. Many limestone and dolomite types (coquinoid, coquinal, algal, and calcarenites, and more common varieties of bedded limestone and dolomite) are found in the lacustrine sediments, but only thin "fluvial" limestone beds are present in the Tertiary rocks of the Uinta Basin. Final conclusions, applicable to a large number of separate continental deposits, are not drawn because studies of this type are still very much in the "gathering stage."