68 FLORIDA GEOLOGICAL SURVEY-THIRD ANNUAL REPORT.
a surface stream to the Apalachicola River. At a distance of three or four miles from the river, this stream, after cutting its channel some depth, reached the Chattahoochee Limestone. When this formation was reached the water passed into the earth, the drainage becoming subterranean. Subsequent erosion carried the basin to its present level.
METHODS OF DRAINAGE.
Two methods of draining basins of this type may be considered.
(I) drainage by surface ditching to some stream or other outlet lying at a lower level: or (2) drainage into the underlying water bearing formation.
DRAINAGE BY SURFACE DITCHING.
Surface ditching usually suggests itself as the more natural method of drainage, and it is often inferred in the absence of definite information that the lakes lie at a higher level than near-by streams. This is not always the case, and such an assumption may lead to a very costly error. A lake or prairie of this type a few miles southeast of Citra was connected many years ago by canal at considerable expense with a tributary of the Ocklawaha River. Upon completion of the canal it was found that the lake basin was at a lower level than the stream bed. The peculiar method of formation of these lake basins by solution, as previously explained, carries them frequently to a lower level than the stream which served in earlier stages as an outlet. Lake Iamonia as previously stated lies practically on a level with the Ocklocknee River, and receives the overflow of that river during high water stages. Alachua Lake basin lies, as shown by the topographic map, at practically the same level as Orange Lake and the headwaters of Orange Creek which served formerly as the outlet.
DRAINAGE INTO THE UNDERLYING FORMATIONS BY WELLS.
Drainage into the underlying formations takes place naturally through the sinks already existing. Artificial drainage consists either in enlarging the sinks, or in making artificial openings in the form of dug or drilled wells through to the water bearing formation. In either case the principle is the same. The underlying limestone is porous and cavernous, and is filled with water to a definite although slightly variable line or level known as the permanent underground water level.