110 FLORIDA STATE GEOLOGICAL SURVEY. 
“Coquina” rock . 330 -331 
Clay .• .. 331 -340 
Blue clay and sand. 340 -350 
Sticky blue clay; very little sand. 350 -358 
Clay with black gravel .... 358 -365 
Blue clay with gravel and shell casts.... 365 -368 
White clay with gravel . 368 -375 
White marl with very little sand .. 375 -385 
Light-colored clay . 385 -390 
Greenish clay . 390 -400 
Greenish sandy clay . 400 -410 
Sticky clay .......410 -428 
Clay with very little sand. 428 -434 
Nearly pure clay; very light when dry. 434 -443 
Bluish sandy clay with gravel and streaks of sticky clay with some 
nodules of rock . 443 -470 
Rock . 470 -470^2 
Greenish clay with fine sand above and coarse sand below; small flow 
of water at 487 feet. 470^4-487 
Rock boulder (siliceous concretion) in blue sandy clay... 487 -492 
White clay .. 496 -497 
Compact blue clay .. 492 -496 
Conglomerate rock . 497 -499 
Hard brownish rock . 499 -504 
Very hard compact rock (siliceous limestone). 504 -510 
Soft white rock with some water. 510 -519 
Hard compact rock . 519 -524 
Very soft white rock in layers 1 to 5 feet thick with strata of more 
compact rock 3 to 12 inches thick; increase in the flow of water 
on breaking each hard stratum. Gaged flow at 632 feet 1,000,000 
gallons in twenty-four, hours.. 524 -727 
Compact brown rock; no water. . 524 -727 
Alternate hard and soft strata of grayish rock with very little water 758 -865 
Soft white rock with hard brown layers 1 to 3 feet thick every few 
feet; a slight increase of flow from each soft layer. 865 -930 
Very hard brown rock . 930 -935 
Soft brownish rock with hard layers, flow increasing as each hard 
layer is broken . 935 -950 
Alternate layers of hard and soft rock; small increase in flow. 950 -970 
More compact rock; no water . 970 -980 
The sands and gravels from 0-34 1-3 feet are probably Pleistocene 
though they may include some Pliocene beds. 
The fossiliferous limestone encountered at thirty-five feet is the 
Jacksonville. The rocks belonging to this formation continue to a 
depth of at least 496 feet. 
Thickness:—The exposures of the limestone of the Jacksonville 
formation seldom exceed five or six feet in thickness, but there is a 
maximum exposure of about fifteen feet at a locality two miles above 
Middleburg on Black Creek. 
