GEOGRAniY OF CENTRAL FLORIDA 119 



7. THE PENINSULAR LAKE REGION 



(Figs. 18-22, 35, 36, 38. Soil analyses 37-45, C-E, J-M.) 



This is the lai"gest and in some respects the most interesting 

 region in central Florida, with an area of about 4,000 square miles. 

 It extends along the axis or "backbone'' of the peninsula from Clay 

 County to DeSoto. County, and has no counterpart in any other 

 state, though 'there is a small lake region in West Florida (describ- 

 ed in the 6th Annual Report) that resembles it in some particulars. 



Geology. Geologists have mapped most of the area as underlaid 

 by Upper Oligocene strata, but that is largely hypothetical, for ex- 

 posure of fossiliferous rock are rare. There are also patches, belts 

 or ^Dockets of Miocene and Pliocene formations in several places, 

 mostly not far from the St. John's River and its tributaries. Rock 

 Spring, in Orange County (fig. 18) is of interest as being the local- 

 ity where the first Miocene fossils were found in Florida.* The 

 vegetation in many low places near lakes and rivers seem to indi- 

 cate limestone or marl near the surface, and there are a few large 

 limestone springs in Volusia, Seminole, Orange and Lake Counties. 



On the summit of Iron Mountain there is a little ferruginous 

 sandstone or conglomerate, a kind of rock common on non-calca- 

 reous uplands in the coastal plain from New Jersey to Texas, but 

 rare in peninsular Florida. A hard sandy clay, usually pinkish or 

 mottled (but bright red around Lake Wales in Polk County), 

 seems to be nearly everywhere present on the uplands, though nat- 

 ural exposures of it are scarce, for it is usually overlaid by a few tc? 

 several feet of loose sand. This clay is used in many places for road- 

 surfacing material, as is some of the marl. Still purer clays are 

 used for brick-making at Whitney, and some kaolin is mined near 

 Okahumpka. There are vast deposits of peat in all the counties 

 (described in some detail in the 3d Annual Report), bordering the 

 larger lakes and rivers and completely filling many of the smaller 

 lake basins. One or two of the peat bogs in Lake County are rich 

 in diatoms, and have been used in a small way for "infusorial 

 earth." 



Topography. The Ocklawaha and St. John's Rivers are border- 

 ed by flatwoods sometimes several miles wide, differing little from 



*See E. A. Smith, Am. Jour. Sci. 121 :309. April, 1881 ; Tenth Census U. S. 

 6:190. 1884; Dall & Harris, U. S. Geol. Surv. Bull. 84:125. 1892; Matson & 

 Clapp, 2nd Ann. Rep, Fla. Geol. Surv. 114. 1909. 



