What indicates that two are dating

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Such features as colour, ripple marks, mud cracks, raindrop imprints, and slump structures are directly observable in the field.

Properties derived from laboratory study include (1) size, shape, surface appearance, and degree of sorting of mineral grains, (2) specific mineral types present and their abundances, (3) elemental composition of the rock as a whole and of individual mineral components, (4) type and abundance of cementing agent, and (5) density, radioactivity, and electrical-magnetic-optical properties of the rock as a whole.

The most useful indication of time equivalence is similar fossil content, provided of course that such remains are present.Failing that, the repetition of a certain layered sequence (e.g., a black shale sandwiched between a red sandstone and a white limestone) lends confidence to physical correlation.Finally, the measurement of a host of rock properties may well be the ultimate key to correlation of separated outcrops.Using fossils simply for identification purposes, Smith constructed a map of the various surface rocks outcropping throughout England, Wales, and southern Scotland.Smith’s geologic map was extremely crude, but in its effect on Earth study it was a milestone.

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