164 Papers from the Marine Biological Laboratory at Tortugas. 



Clapp,^ and I went over it with the two last-named geologists. Thanks 

 to the splendid researches of Dall, no Tertiary horizon is paleontologi- 

 cally better known. 



Besides the exposures along Caloosahatchee River, others are known 

 along streams or the tributaries of streams flowing into Charlotte Harbor, 

 viz: Miakki River, Chiloccohatchee River, Peace Creek, as far north 

 as Zolfo Springs, Prairie Creek, Alligator Creek, and the famous Shell 

 Creek; and along streams that do not flow into Charlotte Harbor, " Rocky 

 Creek, which flows into Lemon Bay, near Stump Pass." ^ Considerably 

 east of Peace Creek beds of marl containing "large clams" have been 

 reported to Mr. Willcox as occurring on the banks of Arbuckle Creek.^ 



The last -mentioned exposure deserves careful investigation, as it is 

 directly in line between the Caloosahatchee exposures and the buried 

 Pliocene of Lake Tohopekaliga. 



It has not so far been possible to differentiate Pliocene from Pleisto- 

 cene and Miocene in the well-borings south of the latitude of the southern 

 end of the Lake Okeechobee, but it is not to be doubted that Pliocene is 

 represented in the wells. The borings, however, do not indicate any 

 great changes of deposition conditions. 



LITHOLOGY AND THICKNESS. 



Both the Nashua and Caloosahatchee marls bear close lithologic 

 resemblance, both consisting of shell marls interstratified with beds of 

 sand. The maximum thickness of the former is about 32 feet at De 

 Land^; that of the latter probably about 25 feet.* 



SHORE-LINE. 



The Pliocene submergence was not so extensive as that of the Mio- 

 cene. The shore-hne lay west of St. John's River from Palatka south- 

 ward to opposite Sanford, whence it continued southward keeping on 

 the west side of Lake Tohopekaliga ; it probably passed around the south- 

 ern end of the ridge on which Haines City is situated, and then turned 

 southwest to the vicinity of Sarasota Bay. Probably the territory east 

 of St. John's River extending from Palatka northward to beyond 

 Jacksonville, was also submerged. There is no evidence of any sub- 

 mergence of the west coast north of Tampa. 



DEPTH AND TEMPERATURE OF THE PLIOCENE SEA. 



Dall has attempted to reconstruct the conditions of depth and tem- 

 perature prevalent during the deposition of the Caloosahatchee marl. 

 He says: 



The assemblage of species on the whole, in the principal stratum, is such as 

 one might expect to find in water from 20 to 25 feet in depth, judging b}^ what we 

 know of living mollusks. Mixed with these are a certain number of shallow-water 

 forms which may be supposed to have flourished as the water became shoal by 



1 Florida Geol. Surv., 2d Ann. Report, pp. 123-128, 1910. 



2 Dall, U. S. Geol. Surv., Bull. 84, p. 148. 



3 Matson and Clapp, Florida Geol. Surv., 2d Ann. Rept., p. 129. 

 * Matson and Clapp, op. cit., p. 124. 



