This paper is a discussion of (1) the preparation of simplified regional stratigraphic map-diagrams and (2) the usefulness of such map-diagrams in the study of the onlap and strike-overlap at known regional unconformities both on the surface and in the subsurface. Such map-diagrams are simpler than the maps from which they are made, but they may contribute greatly to a clear understanding of verifiable geologic history. They are especially useful in studying the position, trend, and rates of truncation and onlap of significant stratigraphic units of regional extent. Their proper field of use is the coastal plain and low-dip "strata-benchlands," especially in marginal cratonic and shelf areas. If they have any usefulness in highly disturbed tectonic zones, it is yet to be emonstrated.

These regional stratigraphic map-diagrams are distortions of the regional geologic-contact maps, because contacts in the diagrams do not have their correct geographical positions. They do have, however, a logical and meaningful geologic position, which I believe contributes to their usefulness in tracing pinch outs into the subsurface.

Certain basic simplifying assumptions are necessary and are presented. A time-distance regional unconformity-diagram illustrates the immutable nature of the elapsed-time value of regional unconformities. Diagrams are presented and discussed, illustrating subsurface trends which are classified as (1) parallel, (2) nonparallel, and (3) complex.