Читать книгу The Men Who United the States: The Amazing Stories of the Explorers, Inventors and Mavericks Who Made America - Simon Winchester, Simon Winchester - Страница 27

This was in 1799. For the next ten years, Maclure tramped and stagecoached relentlessly up and down and across the narrow swath of territory that lay between the Appalachians and the Atlantic—the country’s most known and settled region. He wandered on the far side of the Alleghenies, too, through what is now Arkansas and Mississippi, though it is not certain if he managed to get as far north as the sparsely settled territories of Ohio and Indiana. He managed to get himself all the way down to Georgia. We cannot be certain that he got all the way up to Maine, but he did claim to have crossed the hills and valleys of the Appalachians at least twenty-two times—which, given the condition of the roads at the time, was no mean achievement.

But however he did it, wherever he happened to go, however many miles he walked, rode, or went in greater comfort by carriage and diligence and cart, he achieved something truly memorable, with a significance that went beyond what might have seemed its purely American relevance. He announced it in an address before an evening meeting of the American Philosophical Society in 1809 after offering his first thoughts on the geology of the nation. Crucially, he included with his seventeen pages of explanation a hand-colored map—the first geological map in the world, some say, and certainly the first recognizable geological map of the United States.

It is a document of curious beauty, even though its simple innocence rendered it of little real use. It is based on a topographic map engraved by Samuel Lewis, a Philadelphia mapmaker who was at the time perhaps the country’s preeminent cartographer.¹ Maclure used vivid watercolors—yellow, red, blue, pink, and green—to paint onto the base map’s eastern half the five main divisions, as early geology was inclined to see them, of America’s rocks.

The swaths of color he used—to show different kinds of rock, not different ages, as maps do today—all trend across the states from the southwest up to the northeast. They sweep along in approximate parallel to the lines of the Appalachian hills—which on the map sheet are picked out in caterpillarlike lines of ugly fuzziness; that was the device Lewis had employed to depict chains of mountains on all of his maps.

The results of Maclure’s estimated fifty survey journeys across the Appalachians led to the publication in 1809 of this crude but memorable first geological map of the then United States. It predated by six years the much more famous British map by William Smith.

Four basic types of rock make up the geology of America, as it was described in 1809. On the western side of the mountains, everything on Maclure’s map is colored pale blue, indicating the presence of so-called secondary rocks, fossil-bearing sediments, by and large. On the eastern side, the ocean side, all is by contrast hand-colored yellow, indicating alluvial rocks, gravels and sands and fresh-from-the-ocean clays.

The summits of the Appalachian mountain ranges Maclure showed to be quite geologically different and painted them in vivid streaks of deep blue and deep red denoting what early geological theorists called transition rocks. He also noted the presence of hard granitic outcrops of what he called primitive rocks; these he colored in pink. And for good measure, he also invented a fifth category for deposits of rock salt.

As art, Maclure’s maps—he made a revised version in 1818—are undeniably pretty; but as science, they were confusing and, in truth, pretty useless. Had they been Maclure’s sole achievement, he might then have slipped into obscurity. But that was not to be.