L. C.Johnson — Structure of Florida. 231 



plain, or region of sinks, (3) the u High-Hammocks," or Lake 

 region and (4) the " Eastern-slope " — or region of streams, 

 tributary to the St. John-=. 



The immediate coast on either side is not considered. 



The turning point will be to understand the second, — the 

 region of sinks. 



In the figure, it is represented as a depression, though not 

 always such. Westward it is bounded by a line of sand dunes, 

 continuous at least from Sumter County northward beyond the 

 Santafe River, whence it begins to curve more to the west, 

 and becomes lost in other formations. 



The eastern boundary of the central plain is, in places, 

 sharply defined ; for instance, at Weldon station on the Florida 

 Transit Railway, which is given as the summit or highest point 

 on the line between Jacksonville and Pensacola. This high 

 ridge trends northward into Georgia in the direction of 

 Dupont ; and southward by many curves and scallops to the 

 "Natural Bridge" on the Santafe — to Gainesville, to Okala, 

 to Leesburg. 



The third, or Lake region proper, begins at the Weldon 

 ridge, and on that line of railroad, reaches to Trail-Ridge, — 

 within eighteen miles of Jacksonville. Geographically it is 

 easily defined. In Georgia it is in part represented by the 

 Okefenoko swamp system ; south of the St. Mary's River we 

 have lakes, and the lakes of Florida are numerous. 



Eastward of the elevated region of the Lakes, — the fourth 

 division has a surface of thin sandy soils with many streams, — 

 and with extended " Flatwoods " interspersed with " slashes " 

 which give rise to streams. This is presented as a geological 

 division, because it is believed to be constituted in the main of 

 newer Tertiary formations, but being as yet unexplored, very 

 little can be definitely said of it. Taking the data derived 

 from the artesian wells bored at Palatka, St. Augustine, Jack- 

 sonville and other places, these Neocene deposits have an aver- 

 age thickness of about 300 feet. 



Returning to the consideration of the second division : All 

 later observations go to sustain the geological horizon assigned 



