136 FLORIDA GEOLOGICAL SURVEY—THIRD ANNUAL REPORT. 
where the “Trail Ridge” forms part of the boundary. A narrow 
strip along this part of the county exceeds ioo feet in elevation. 
With this exception practically all parts of this county lie below 
the ioo foot contour line, while much of the area lies below the 
25 foot contour line. 
The elevations in Nassau and Duval Counties have been ob¬ 
tained from various sources. An important line of levels extend¬ 
ing from Trout Creek across Nassau and Duval Counties in a 
southwesterly direction, made during the summer of 1909 in con¬ 
nection with a preliminary survey for a ship canal across Florida, 
were kindly made available for this purpose in the office of the 
United States Engineers at Jacksonville. Similar surveys made by 
the same office in 1879 supplied elevations from Fernandina to 
Maxville and at various points along the St. Marys River.* in 
addition much information as to elevations has been obtained f;om 
the profiles of the several railroads crossing this section, particu¬ 
larly the Seaboard Air Line from Jacksonville to Maxville, the 
Florida East Coast from Jacksonville to Mayport and the Atlantic 
Coast Line from Jacksonville to the St. Marys River. 
From Jacksonville westward the rise in elevation as shown by 
the profile of the Seaboard Air Line Railway is very gradual to a 
point three miles west of Jacksonville where an elevation of 27 feet 
is reached. From this summit the elevation drops off slightly, the 
elevation of Cedar Creek being 17 feet. Beyond Cedar Creek the 
elevation rises more rapidly. Marietta station is approximately 60 
feet above sea. The summit of this rise is reached two miles west of 
Marietta where the elevation is 94 feet. White House station is 
82 feet above sea. Beyond McGirts Creek one and one-half 
miles an elevation of 91 feet is reached. From this point there is 
a very gradual slope to Baldwin, this latter place being 86 feet above 
sea. 'South from Baldwin the contour rises in general reaching an 
elevation of 93 feet at Maxville and 100 feet one-half mile beyond 
the county line. 
The line of levels run by United States Engineers extends 
from Trout Creek passing just to the south of Brandy Branch sta¬ 
tion, or Bryceville postoffice. The summit elevation in Nassau and 
Duval Counties along this line occurs about four miles northeast 
of Brandy Branch, where an elevation of 90 feet is recorded. 
WATER-BEARING FORMATIONS. 
The deeper wells in Duval County reach and terminate in the 
Vicksburg Limestone. This is known to be the case at Jackson- 
* Annual Report for the Chief of Engineers for i88o 3 pp. 973-1010. 
