Inventions, Development, and Tycoons The rapid economic development following the Civil War laid the groundwork for the modern U.S. industrial economy. An explosion of new discoveries and inventions took place, causing such profound changes that some termed the results a "second industrial revolution." Oil was discovered in western Pennsylvania. The typewriter was developed. Refrigeration railroad cars came into use. The telephone, phonograph, and electric light were invented. And by the dawn of the 20th century, cars were replacing carriages and people were flying in airplanes. Parallel to these achievements was the development of the nation's industrial 25

infrastructure. Coal was found in abundance in the Appalachian Mountains from Pennsylvania south to Kentucky. Large iron mines opened in the Lake Superior region of the upper Midwest. Mills thrived in places where these two important raw materials could be brought together to produce steel. Large copper and silver mines opened, followed by lead mines and cement factories.