Chipola Sea. It was created by rising sea level flooding the area once again. The Torreya Formation, a geologic formation extending from Gadsden to Hamilton County was established during this period. A somewhat narrow land bridge exists with a width from Madison County to Duval County, Florida extending into Georgia. The Middle Miocene Disruption, an extinction of many mammal genera begins. A very short dry period follows the Chipola lasting possibly 1 million years. During the time the Middle Miocene Disruption continues. Forests slowly draw in massive amounts of carbon dioxide, gradually lowering the level of atmospheric from 650 ppmv down to around 100 ppmv. Walton Subsea Period: Miocene. Geologic stage: Early Serravallian through early Tortonian ~12.00—7.2 Ma., approximately . Animal age: Clarendonian ~13.6—10.3 Ma through Hemphillian ~10.3—4.9 Ma. Post-Walton dry period: Early Tortonian ~10.0—9.0 Ma. The Walton Subsea was named for the fossil beds of Walton County. Alaqua Subsea Period: Miocene. Geologic time period: Mid Tortonian through mid Messinian ~7.246—5.332 Ma., approximately . Animal age: Hemphillian ~10.3—4.9 Ma. Post-Alaqua dry period: The late Messinian through Zanclean ~5.332—3.6 Ma. The Alaqua Subsea was named for the fossil beds found along Alaqua Creek, Walton County. The period of time after the Alaqua experienced a somewhat long dry period. A major event was the Messinian salinity crisis or dry Mediterranean. It was replenished with the Zanclean flood which raised the world-wide sea level 10 meters or 33 feet. Jackson Subsea Period: Pliocene through Pleistocene. Geologic time period: Piacenzian through Blancan ~3.600—2.588 Ma., approximately . Animal age: Blancan ~4.9—1.8 Ma. Post-Jackson dry period: Piacenzian through Holocene ~2.588 Ma. —present. The Northern Hemisphere is in a full ice age with its final retreat around 11,000 years ago. The Jackson Subsea was named after the Jackson Bluff Formation and formerly called the "Jackson Sea." It was created during the rise in sea level during the Pliocene. During this period the last glacial period known as the Wisconsin ice age begins. References Petuch, Edward J., Cenozoic Seas: The View from Eastern North America, Taylor & Francis Group, 2003, , Geology of Florida Natural history of Florida