Because sand is much less compactible than clay, thick lenses of sand surrounded by shale, when buried under a load of later sediments, are marked by low anticlinal bulges. This principle has been used successfully for several years in Kansas for tracing lenticular sand bodies of both the channel and the offshore-bar types. Extremely detailed structural mapping is necessary to reveal these bulges, and they can not always be distinguished from similar structures produced by other causes. Good exposures of evenly bedded rocks at the surface are essential, and lenticular sands at horizons above that at which production is sought may be a source of confusion. Elimination of regional dip is a valuable aid in interpretation. While it seems that every thick sand body is represen ed by a bulge, not every structural feature which might be so interpreted represents a buried sand body. Consequently, the experience and judgment of the geologist play a large part in the successful use of this method.