REPORT OF INVESTIGATIONS No. 40


of latitude and 1-minute meridians of longitude. The wells in a 1-minute
quadrangle are numbered consecutively in the order inventoried. In
Florida, the latitude and longitude prefix north and west and the first
digit of the degree are not included in the well number.
 The well number is a composite of three numbers separated by
hyphens: the first number is composed of the last digit of the degree
and the two digits of the minutes that define the latitude on. the south
side of a 1-minute quadrangle; the second number is composed of the
last digit of the degree and the two digits of the minutes that define
the longitude on the east side of a 1-minute quadrangle; and the third
number gives the numerical order in which the well was inventoried in
the 1-minute quadrangle (fig. 3).

 GEOLOGY
 GENERAL STATEMENT
 In Escambia and Santa Rosa counties, a thick sequence of sand,
gravel, and clay extends from the surface to as much as 1,000 feet
(fig. 4). Nearly all the wells in this area tap permeable sediments within
this sequence-referred to as the sand-and-gravel aquifer (Musgrove,
Barraclough, and Marsh, 1961). In the northern half of the area, the
sand-and-gravel aquifer lies on the upper limestone of the Floridan
aquifer, but in the southern part, the two aquifers are separated by a
thick clay unit of Miocene age which serves to confine the water that
is present in the upper limestone of the Floridan aquifer. An extensive
clay bed, the Bucatunna Clay Member of the Byram Formation, under-
lies the upper limestone of the Floridan aquifer and forms an aquiclude
throughout the area (Marsh, 1962).'the lower limestone of the Floridan
aquifer underlies the Bucatunna and rests upon relatively impermeable
clay and shale. Within the area, no fresh-water aquifers occur below the
lower limestone of the Floridan aquifer. A more detailed report of the
geology of the Florida Panhandle was prepared by Marsh.

 COLLECTION OF DATA
 Information has been collected on about 600 water wells in this
 area. Figure 5 shows the location of the wells in Escambia and Santa
 Rosa counties. They range in depth from about 15 feet to over 1,800
 feet but most of them are between 30 and 300 feet deep. They range in
 diameter from 1%i inches to 30 inches. Most of the domestic-supply wells
 are 1, to 4 inches in diameter and most of the industrial supply wells are