Friday, January 25, 2008

Colors


In 1815, a self-taught geologist named William Smith published the first geological map of a sizable part of the Earth's surface, the island of Britain. The map was 8 feet by 6 feet, published in 16 separate sheets. Four hundred copies were printed, many of them hand-colored by Smith himself.

A reduced-size poster of Smith's map is available from the Liverpool Geological Society. Placed side by side with a modern geological map of Britain (above), one sees how much Smith got right; the geology is almost identical. The modern map also follows the color scheme invented by Smith for designating different kinds of rocks.

One of my favorite things to do when I taught earth science was to take my students on an imaginary walk across southeastern England, along the line of zero longitude, using the big modern geological map as a guide. I drew a multicolored cross-section across 20 feet of chalkboard, showing the ups and downs of the landscape, the sights we might see along the way, and the rocks we would find exposed at the surface of the Earth.

Then I asked the students to guess at the three-dimensional arrangement of strata that would explain what we saw on the surface. Now the colored chalk came out in force, as we hypothesized sweeping folds of rock -- mostly sandstone and mudstone -- rising and falling across the chalkboard. We ended our imaginary walk where William Smith ended his remarkable mapping achievement, with a grand view of the changes that have taken place on the surface of the Earth over eons of time.

After years of taking the imaginary walk, I decided to do it with boot to the sod. Knapsack on back, I walked from the Channel to the North Sea, visiting along the way sites of interest to the history of science. This is the story I tell in Walking Zero: The Discovery of Cosmic Space and Time Along the Prime Meridian.