When the English colonists were first exploring Virginia, they quickly explored up the rivers as far as their ships could float. In 1607, Christopher Newport sailed up the James River to the location of what is now Richmond, before returning to England and reporting on his success at delivering 104 colonists to a new settlement called Jamestown.
A year after unpacking the Susan Constant, Discovery, and Godspeed and building a fort at Jamestown, the English had sailed or rowed up the James, York, Rappahannock, and Potomac rivers to the line of waterfalls known today as the Fall Line. John Smith reached the current location of Alexandria in 1608 in a small boat known as a shallop.
The waterfalls and rapids of the Fall Line blocked the English from sailing further west into the North American continent, and of course prevented the English from discovering a Northwest Passage permitting ships to sail through Virginia to China.
The Fall Line is the western edge of the Coastal Plain, the physiographic province where tides affect the water level in the rivers and where ocean-going vessels can sail in the Virginia rivers. One indication of the constraint to transportation imposed by the Fall Line: Smith could not get his shallop across Little Falls near the current location of Georgetown, so he did not discover the very distinctive Great Falls further upstream.
Naturally the English immigrants to Virginia initially settled east of the Fall Line, with easy access to Europe and the Caribbean. The English colonists cleared the forest and started plantations in the flat Coastal Plain close to the Chesapeake Bay - so as a result of the waterfalls, the English expelled the Algonquian-speaking tribes that lived in Tidewater Virginia long before forcing the Native Americans that spoke Siouan or Iroquois languages from their towns west of the waterfalls.
Settlement west of the Fall Line imposed a substantial transportation burden on the colonists. East of the waterfalls in the Chesapeake Bay watershed, the English could roll heavy hogsheads of tobacco from barns to a wharf and load the barrels of "smoking leaf" directly onto ships headed to Europe. West of the waterfalls, the hogsheads had to be rolled uphill/downhill on unpaved colonial roads to the Fall Line, or tobacco had to be hauled to a river, loaded onto small boats (batteaux), floated to the Fall Line, moved off the small boats onto wagons, carried a few miles on unpaved roads around the waterfalls, then loaded onto ocean-going vessels at the ports below the waterfalls.
As the population of the Virginia colony increased, towns developed at the waterfalls. The end of water navigation was a good place to unload European goods to ship to settlements further inland - hey, why load a wagon to carry anything heavy or bulky on the lousy Virginia roads, when you could sail upstream? Once the river was blocked by a waterfall, however, it made sense to unload the ship and use wagons.
Our history and current cultural patterns in Virginia might have been very different, if there had been a tall range of mountains just west of the Chesapeake Bay. European immigration into Virginia was a slow migration westward, as settlers converted "virgin wilderness" into farms incrementally for a century. Europeans planted tobacco, a bulky crop that had to be transported to ports or wharves before being shipped to markets across the Atlantic Ocean.
Can you recognize the impact of the Fall Line and the Blue Ridge in the colonial settlement of Virginia, reflected in the formation of counties as immigrants moved west?
Had Virginia's topography made transportation far more difficult, colonists might have grown a range of crops that could be processed and used locally. If the Fall Line had been a high range of mountains, and access to international shipping had been too expensive for immigrants that crossed the mountains, perhaps colonial Virginia might have created a diversified farm economy. Instead, Virginia colonists emphasized staple production of just one crop sold for export. The colonists also created a legal system to support the use of slave labor to grow that tobacco cheaply, in addition to creating the first representative government in the New World (starting with the House of Burgesses meeting in Jamestown in 1619).