154 FLORIDA GEOLOGICAL SURVEY-THIRD ANNUAL REPORT.
210 feet above sea. Newburg and Brooklyn, in the lake region of the southwestern part of the county, have elevations, as recorded by the Georgia Southern and Florida Railway, of 155 and 157 feet respectively.
WATER-BEARING FORMATIONS.
Most of the flowing wells of Clay County terminate in the Vicksburg Limestone. The first flow at Green Cove Springs, in the eastern part of the county, is obtained at a depth of from 325 to 400 feet.
The Miocene formations underlie much if not all of Clay County. In the pit of Union Brick Company at Middleburg the following section was observed:
Loose sand and soil .................... ........... I foot
Sandy clays oxidized red ................................ 7 feet
Blue sticky clay, comparatively free from sand................. io feet
Light-colored sands ............................ 3 feet
The clay exposed in this pit is probably the same as the clays in the clay pit Pear Jacksonville (p. 90). Beneath these clays, as indicated by well borings, calcareous and phosphatic Miocene rocks are encountered. This part of the Miocene, the Jacksonville formation, is exposed at many localities along Black Creek and its tributaries. The section exposed at High Bluff, on the south fork of Black Creek about five miles above Middleburg, has already been given.
Other exposures of this formation were noted at the following localities along the river. At Fowler's Landing on the south fork of Black Creek, three miles above Middleburg, fifteen feet of the Jacksonville formation is exposed. At Buddington's Landing. one and one-half miles above Middleburg, seventeen feet of the Jacksonville formation is exposed. Hogan's Landing, just below Middleburg, shows twenty-eight feet of the Jacksonville formation. A bluff at the mouth of the south fork shows twenty-five feet of the Jacksonville formation. A bluff on the north bank of the north fork one and one-half miles from Middleburg, shows three feet of the Jacksonville formation.
AREA OF ARTESIAN FLOW IN CLAY COUNTY.
The area of artesian flow in Clay County is confined to that portion bordering the St Johns River and its tributaries. As has