| A | B |
|---|
| tributary | a river or stream flowing into a larger river or lake |
| headwaters | a tributary stream of a river close to or forming part of its source. |
| fall line | a narrow zone that marks the geological boundary between an upland region and a plain, distinguished by the occurrence of falls and rapids where rivers and streams cross it. |
| fossil fuel | a natural fuel such as coal or gas, formed in the geological past from the remains of living organisms. |
| hurricane | a large cyclonic (spinning) storm |
| immigrate | to move into an area from somewhere else |
| Underground Railroad | network of secret routes and safe houses established in the United States during the early-to-mid 19th century, and used by African-American slaves to escape into free states and Canada |
| dry farming | a method of farming in semiarid areas without the aid of irrigation |
| megalopolis | a very large, heavily populated city or urban complex. |
| smog | fog or haze combined with smoke and other atmospheric pollutants. |
