42 
Carter R. Gilbert 
Vernon 1964: Fig. 5). This upland area is limited on the south and east 
by an out-facing scarp, a marine terrace about 30 m above present sea 
level that is the most persistent topographic break in the state. In Flor- 
ida this is called the Cody Scarp, a name that is synonymous with Alt’s 
(1968) “Surry Scarp”; the same feature was referred to as the “Wico- 
mico Shoreline” by Cooke (1945) and by Hoyt and Hails (1967). In 
Florida the Cody Scarp extends almost straight eastward to a point in 
the upper Suwannee River valley, just east of the Alapaha River, 
beyond which it turns southward at about a 75-degree angle to a point 
not far southwest of Gainesville, curves eastward to run just north of the 
Oklawaha River, and then turns abruptly northward west of the St. 
Johns River (Burgess and Franz 1978) (Fig. 3). The area so defined, the 
“Wicomico Peninsula,” borders Trail Ridge, which is a beach ridge 
formed along its eastern margin. The “Wicomico Peninsula” also borders 
the Duval Upland and Baywood Promontory, which developed as 
regressional plains just beyond the eastern margin of the scarp as sea 
levels dropped (Fig. 3). 
The continuity of the Cody Scarp is unbroken except by the valleys 
of major streams, but its definition is variable. In many places it can be 
delineated with unequivocal sharpness, whereas elsewhere it appears as 
a gradual reduction of average elevation and a general flattening of ter- 
rain as lower elevations are reached. Swift et al. (1977) indicated that in 
the Ochlockonee River valley elevations above sea level range from 60 
to 90 m in the highlands immediately surrounding the drainage, and are 
30 m or less in the lowlands. These two areas are separated by the scarp. 
Northward the highlands remain hilly but more rolling, and the tribu- 
taries have more mature, meandering channels. To the south the land is 
flat and streams are sluggish and swampy, but where streams flow over 
the scarp they have steeper gradients. 
The Cody Scarp forms an important zoogeographic boundary. 
Swift et al. (1977: 61) cited 12 fish species whose distributions in the 
Ochlockonee drainage seem to be affected by it, including Enneacanthus 
obesus, Heterandria formosa , Fundulus chrysotus , Fundulus cingulatus 
and Leptolucania ommata (all restricted to below the scarp); Notropis 
petersoni (found only immediately above); and Ichthyomyzon gagei , 
Semotilus thoreauianus and Etheostoma swaini (all essentially con- 
fined to the scarp area) (Lee and Gilbert 1980b; Martin 1980; Shute 
1980; Gilbert and Burgess 1980d,f; Swift 1980a; Rohde and Lanteigne- 
Courchene 1980; Lee and Platania 1980; Starnes 1980). The influence of 
this topographic feature is best illustrated, however, by the distribu- 
tional and systematic relationships of two closely related but easily dis- 
tinguishable cyprinodontid fishes, Fundulus escambiae and Fundulus 
lineolatus (Rivas 1966; Wiley 1977, 1980b, c) (Fig. 7). Fundulus escam- 
biae is an eastern Gulf slope species that ranges from the Perdido River 
