Earth Science Essentials
by Russ Colson
Stratigraphy provides a means to find and follow ore deposits underground, to know where to build dams or canals, and especially where to look for the precious black gold that built our modern society.
Many principles of early stratigraphy were worked out by William Smith, an English surveyor and engineer, who was employed to identify the best courses for canals and drainage ditches. His recognition that layers of rock occur in particular sequences and that layers representing different time periods contain distinct assemblages of fossils allowed him to accurately predict locations and thickness of various types of rock important to his survey work and to become a widely known and respected surveyor in England in the early 1800's.
Simon Winchester, in his best-selling book "The Map that Changed the World" wrote that William 'Strata' Smith's diaries reveal how he learned to identify the layers where coal might be expected. The rocks, Smith wrote, always appeared in the same sequence (near Radstock England). There is a sandstone, a siltstone, a mudstone, and then the Temple Cloud Coal seam. Then another sandstone and siltstone and two more coal seams. This provided a vertical, as well as surface, map for where to look for coal.
Fossils were the key to identifying the regular sequence of rock layers. In Smith's words "...each stratum contained organized fossils peculiar to itself, and might, in cases otherwise doubtful, be recognized and discriminated from others like it..." Using each layer's unique fossils, and the repeated sequence of rock types, Strata Smith was able to correlate rocks across England with those he first found near Radstock.
Today we use stratigraphy to predict where to find the treasures of the Earth, not only where at the Earth's surface, but how far beneath the surface.
Oil companies drilling for oil have to know exactly where they are in the stratigraphy, and which layer to look for oil. Without that vertical map, drillers would be drilling blind.
Where would you go in England to find the following fossils, based on Strata Smith's map and fossil successions? (documents from Strata Identified by Organized Fossils (1816) by William Smith courtesy of the University of New Hampshire Earth Science Department)
Last updated March 2, 2015. Pictures and text property of Russ Colson except as noted.