GEOLOGICAL OBSERVATIONS MADE BY THE LEWIS AND CLARK EXPEDITION IN NORTH DAKOTA

The objectives of the Lewis and Clark expedition, as stated in Thomas Jefferson’s June 20, 1803 letter of instructions to Meriwether Lewis, included what today would be referred to as geological observations. Lewis and Clark and other members of the expedition made these types of observations in their journal entries during their journey through the area that is now North Dakota. Their observations fall within many of the major disciplines of geology including: geomorphology, sedimentology, stratigraphy, petrology, hydrology, paleontology, and economic geology. Lewis and Clark demonstrated a keen sense of observation when identifying minerals and the composition of rocks and gravels; identifying rock types such as granite, sandstone, limestone, flint, salt, coal, and clinker. In addition, they noted the presence of landslides, compared the clarity of water from different rivers, and described geomorphic features. They noted a stratigraphic color change in Paleocene age rocks that is used today as criteria to differentiate lithostratigraphic units. They made several insightful comments concerning geologic processes, including erosion, how clinker and petrified wood are formed, the creation of river valleys, what suspended loads and bed loads of rivers can indicate about the surrounding countryside, and the significance of river-terrace deposits. Lewis and Clark observed and speculated about the quality of lignite, Glauber salt, and the agricultural potential of areas along the Missouri River. They were also the first to collect rock, mineral, and fossil specimens in North Dakota for scientific purposes. They sent these specimens back to Thomas Jefferson from North Dakota on April 7, 1805 and a few still exist today.