Picture yourself during colonial times, searching for a spot to start a new settlement. Why just plunk your cornerstones down anywhere when you could have the perfect town site? Among other amenities, this ideal spot might feature:
- a river that is navigable all the way to the Atlantic,
- rapids and falls to power saw mills and grist mills,
- maybe even a little elevation to build houses above the mosquito-thickened swamps in the lowlands.
It’s no coincidence that cities like Richmond, Virginia; Washington, DC; Trenton, New Jersey; and Hartford, Connecticut, all boast just these features. From Georgia to Massachusetts, these and other cities are lined up like a string of stars along an important geologic boundary called the Fall Line. The Fall Line is where the hard rock core of the piedmont and Appalachians meets the soft sediment of the coastal plain.
Those city founders knew a good thing when they found it. In Richmond, for example, the story goes that “in 1607, after 10 days of travel up Powhatan’s River (later known as the James River), Captain John Smith and 120 men from Jamestown, Virginia, settled at the river’s highest navigable location.” (http://www.u-s-history.com/pages/h3916.html). Further north, Lowell, Massachusetts, became a thriving industrial town, especially for textiles, and as noted in the city history (here), “Its earliest history and development are anchored on the Pawtucket Falls.”
Townsites that Rock
Grab a map and try a connect- the-dots between these Fall Line cities (a suggested activity for your students, too). Congratulations – you’ve created a simple geologic map. Here’s one of Virginia, showing the Fall Line, with an excellent overview discussion, too.
When rivers flow over that boundary between ancient hard rock and relatively young, soft layers of sediment, they literally fall off the edge of the (old) continent into the geological coastal zone. Great Falls on the Potomac River cascades 70 vertical feet, yet within a few miles the river becomes the placid, cherry blossom lined tidal waterway we know in Washington DC. Virginia’s capital, Richmond, is built along the banks of the James River where it dashes over the falls of the James River into navigable water. Augusta, Georgia, of golf tournament fame, is another colonial settlement created along the fall line, the furthest boats could get up the Savannah River.
These places provided town founders with the hydropower to develop industry, and the navigable shipping access for trade and supply. In short, the geologic setting provided the foundation for economic and social success.
Since I’m originally a geologist I get particular satisfaction knowing that geology exerts such a strong influence on human settlement. With your students, and some hints below, explore some other examples, subtle and not so subtle.
Have students compare a geologic map of the east with a road map. What cities line up on it? (Hint: Interstate 95 roughly follows the Fall Line).
Very simple map showing the coastal plain vs. Appalachians (does not show rock types) may suffice: e.g. http://www.sagessite.com/usgeog.htm
This more detailed map is a 1960s geologic map from the United States Geologic Survey, from this website.
The Fall Line is just one example of how geology influences human settlement and economic patterns. Other ways include bedrock control on topography, (such as valleys and ridges), availability of groundwater or surface water, ease or difficulty of access (flat land is easier to build roads across unless it’s marshy), and location of mineral resources.
Have students select a state. Consider one city or overall population patterns. With some research into the city history, local natural resources, or geology (check each states geological survey), identify topographic or geologic factors that might have influenced the location of these settlements.