94 REPORT OF INVESTIGATIONS NO. 50
the rock from areas of recharge to areas of discharge. The entire aquifer has been affected to some degree by the dissolving action of ground water and is somewhat analogous to an enormous sponge.
Some of the largest known caverns in Florida have been found within the Floridan aquifer in Orange County. One of the largest caverns with no opening to the surface ever discovered in Florida was encountered in a city supply well drilled in the southwest part of Orlando. This cavern was 90-feet high with the ceiling 578 feet below the land surface. The cavern was filled with water and there was 12 feet of black organic muck on its floor. The areal extent of this cavern is unknown, but several deep wells 1,000 feet to the north did not penetrate it. One of the deepest and largest known caverns in Florida is a sinkhole near Little Lake Fairview, northwest of Orlando, known as Emerald Springs. Emerald Springs was measured in 1956 and found to extend 33884 feet below the water surface which is about 45 feet below the surrounding land surface. According to divers who have explored the sinkhole, it has sloping sand-covered sides for 45 feet below the water surface and then a vertical neck, about 20 feet in diameter, through limestone for about 45 feet. Below this depth, there is a large room with a sloping ceiling. The wall of the room was found at a distance of 89 feet in one direction but had not been found at a distance of 100 feet in the opposite direction (when the divers were forced to return to the surface).
Zones of the Aqulfor
The Floridan aquifer in central Orange County has two major producing zones that are separated by a relatively impermeable zone. The upper producing zone extends from about 150 feet below the land surface to about 600 feet. The lower producing zone extends from about 1,100 feet to 1,500 feet or more below the land surface. Both major producing zones are composed of hard brown dolomitic limestone or dolomite and relatively soft cream limestone; however, the top half of the upper zone is mostly soft limestone. Some of the dolomite in botlh major producing zones is very dense, but many interconnecting solution cavities make the overall permeability of both zones very high.
The limestone in the top half of the upper zone is mostly white, soft, granular. and fossiliferous. This limestone contains cavities, but they are usually neither as large nor as numerous as the cavities in the dolomitic parts of either major producing zone. At