Geologic maps represent the flashier side of earth science. They depict in vibrant colors and funky shapes the rocks and sediments that cover our planet — materials which are often decidedly duller in reality. But though beautiful to behold, the real value of geologic maps lies in their utility.
That’s because the information contained in geologic maps tells scientists more than where to find outcrops of sandstone or granite or basalt. It reveals how different rock types are related in space and, thus, in time, which sheds light on the processes that have shaped our planet.
In the early 1800s, scientists working in the nascent field of geology lacked a sophisticated understanding of these processes. But that began to change 200 years ago, when an Englishman named William Smith published what some argue was the first true geologic map in 1815. His contribution was remembered in Science magazine last week.
Unlike many of the gentleman scientists who ruled the day, Smith had a modest upbringing, the son of a blacksmith in rural Oxfordshire. He became a surveyor, first working on coal mines then canals. His job gave him a unique perspective on the geology of England; it took him all around the country, and also, into the depths of the Earth, where few ever go. Canals, in particular, offered a window into the 3-dimensional structure of the land.
As he worked, Smith began to recognize familiar looking rocks in distant places. He also noticed that the rock layers always occurred in the same order, and tilted at a predictable angle. He suspected they were all related, but he needed more evidence.
Smith’s great insight was to use the fossils in rocks to positively identify specific formations. Many contained the remains of shelled creatures — like spiral ammonites and clam-like bivalves — and Smith used the unique collection of species in each layer to link them across the island or tell them apart.
Geologists still use this technique, known as the Principle of Faunal Succession, to define distinct rock units — indeed, it forms the basis for the geologic timescale, where the emergence or disappearance of a particular species often defines the boundary between geologic periods.
But this would come much later, long after Smith’s death. First, Smith had to compile his observations. He collaborated with a mapmaker named John Cary, who had already developed a topographic map of England, and a crew of watercolor painters, who gave the rock layers their distinctive shading, which indicated the bottom of each formation.
He published his first map in 1815, descriptively entitled, A Delineation of the Strata of England, Wales, and Part of Scotland. Nearly 9 feet tall and 6 feet wide, it came with a detailed explanation of the rock units and their characteristics, as well as a small cross-section, showing how the layers would look if you sliced open the Earth like a cake.
Although maps of rock and mineral locations had been published before, none covered so much ground and captured the fundamental concepts of geology the way this one did — the continuity of layers, the vertical stacking of formations, and the role of fossils. It was powerful; for instance, the map indicated where to find coal, which was in high demand at the onset of the Industrial Revolution.
For a while, the scientific community resisted Smith’s ideas. In the interim, he continued to survey more locations and update his map, and suffered the fate of many intellectual trailblazers — he languished in poverty, and even spent time in debtor’s prison. Eventually, however, people realized he was on to something. In 1831, the Geological Society of London recognized his achievements, and the king gave him a lifetime pension.
But Smith’s legacy continues even today. His map laid the groundwork for 200 years of research that would reveal, among other things, the age of the Earth, the evolution of species, and the theory of plate tectonics. Not bad, for a map.
Learn more about how rocks are deposited in our module on the Rock Cycle.
Check out some amazing geologic maps of National Parks, compiled by Wired, which has a whole series of map stories.
If you are feeling extra inspired, check out a book on Smith’s life and work, called The Map That Change The World by Simon Winchester.
Written by Julia Rosen
Julia Rosen is a freelance science writer and PhD student at Oregon State University. She received a Bachelors degree in Geological and Environmental Sciences from Stanford University before beginning her doctoral research on polar ice cores and climate change. In between, she did her Master's in backpacking around the world and skiing. Julia is a periodic contributor to Oregon States research magazine, Terra, and helps write blog content and develop learning modules for Visionlearning.