(85PTS)
The three Florida shocks of doubtful seismic origin rumbled through the Everglades -La Belle -Fort Myers area in July 1930, Tampa in December 1940, and the Miami -Everglades -Fort Myers area in January 1942. Most authorities attribute these incidents to blasting, but a few contend they were seismic.

http://earthquake.usgs.gov/earthquakes/states/florida/history.php
Abridged from Earthquake Information Bulletin, Volume 3, Number 5, September-October 1971. USGS

What is the central idea of the last paragraph?

Earthquakes happened in Fort Myers and Miami.
Earthquakes only occur from natural seismic causes.
There was blasting in the Everglades in the 1940s.
Three shocks in the Everglades were probably not earthquakes.