This boulder, shown on the shore at Siccar Point, Scotland, is part of the Old Red Sandstone Formation. About 400 million years ago, before there was an Atlantic Ocean separating the Americas from Eurasia and Africa, the Caledonian and Appalachian mountain ranges were formed. Sediments from these mountains accumulated in basins on their flanks. These sediments are collectively known as Old Red Sandstone. Today, long after the continents have been separated by the opening of the Atlantic Ocean, the matching belts of Old Red Sandstone in Scandinavia, the United Kingdom, and the American Northeast, provide compelling evidence for plate tectonic movements.

"The Earth is a book, its story is written in pages of rock." —Dr David Levy

The boulders and molds collected on the expeditions below tell stories of how scientists interpret the record of Earth processes preserved in the rocks. These processes include records of changing landscapes: including the deposit of sediments, uplift of mountains, and erosion by rivers.

October 1998

Jim Webster and Graham Stewart go on expedition to the Grand Canyon and surrounding area with Museum coworkers and a team of mold makers to make a cast of sedimentary layers and features, and to collect boulders of sandstone and limestone. The layers and features of these sedimentary rocks provide a vast amount of information that allows geologists to interpret, or "read," the rocks. A Scientists at Work video featuring Jim and two geologists who specialize in the geology of the Grand Canyon is also shot during this expedition.

June 1998

Heather Sloan and Graham Stewart travel to Scotland with a team of mold-makers to make a cast of the famous Hutton Unconformity. In the 19th century, James Hutton, often called the "Father of Geology" used this outcrop in Siccar Point, Scotland as evidence of his notion of an "unconformity," or preserved gap in time, in the geologic record. Christened the Hutton Unconformity, this outcrop shows red sandstone over shales and reveals a gap of 20 million years in the sedimentary record. An unconformity usually results from a change from a depositional environment to an erosional environment.