possibly farther. Inland it thing and interfingers with the sandy, shelly Caloosahatchee marl which, in the upper part of the Everglades, contains highly mineralized water, the modified remnants of bodies of ocean water entrapped there during the high-sea levels of the Pleistocene, or Great Ice Age. The amount of water that percolates from the northern and middle part of the Everglades through the Caloosahatchee marl down gradient into the Tamiami formation is of very little consequence. The water stored in the aquifer is mostly derived from rainfall falling over the area underlain by the aquifer itself.
Quality of the Ground Water.--The quality of the ground water in
the highly permeable aquifer is fairly uniform. The hardness ranges from about 200 to 300 parts per million and averages about 250 parts per million. The normal concentration of chloride is from about 20 to 30 parts per million. Practically all of the ground water is colored with organic matter, but in varying amounts and with little relation to depth. The color is derived from peat, muck, and other organic matter.
Ground water in the coastal ridge north and south of Miami contains somewhat less dissolved mineral matter and is a little less hard, but in other respects has about the same general character as ground water in the
Miami area.
In the Everglades west and northwest of Miami the ground water is of poorer quality than in Miami. In general, the farther west and northwest that wells are developed, the poorer will be the quality of the water they yield. Hardness and concentration of dissolved mineral matter are considerably greater in the Everglades than along the Atlantic coastal ridge. See plate 3 which graphically represents the quality of water from different