164 FLORIDA GEOLOGICAL SURVEY I3TH ANNUAL REPORT 



narrow barrier-beaches, with lagoons one to five miles wide be- 

 tween them and the mainland. On these beaches the wind has 

 piled up low sand dunes, rarely exceeding lo or 15 feet in height, 

 which seem to be moving very little at the present time. (Dunes 

 are not as well developed in Florida, or anywhere in the tropics, 

 apparently, as they are north of latitude 40°, perhaps because in 

 our climate the vegetation covers the sand too quickly for the wind 

 to disturb it much. The wind has considerable force on the east 

 coast, however, as is indicated by the pines leaning inland at an 

 angle of ten degrees or more in many places.) 



A mile or two back from the shore, at many places along^ the 

 east coast and also near Cedar Keys, Bayport, and probably else- 

 where on the west coast, are old dunes of thoroughly leached white 

 sand, which must have been formed at a time when the land stood 

 a little lowter and the peninsula was narrower, for dunes do not 

 seem to be forming at present more than half a mile from the outer- 

 most beaches. The absence of such features farther in the interior 

 would seem to indicate that the land has not been depressed much 

 below its present position for a very long time ; long enough for the 

 wind to level any dunes that might have existed and for the sala- 

 manders and other animals to mix the pure sand with the darker 

 sub-soil.* 



Other shore features. The absence of barrier beaches along the 

 Gulf hammock coast has been commented on in the description of 

 that region. It seems to be correlated with the very gentle slope 

 of the ocean bottom along there, which keeps the waves from beat- 

 ing on the shore just as if there was a barrier beach a few miles out ; 

 but just why that type of shore with a minutely irregular marshy 

 border, should be confined to the Gulf hammock region is an un- 

 solved problem. Very likely if there was as much wind on the Gulf 

 coast as on the Atlantic coast the shore would be different ; but there 

 is evidently not, for the pines grow perfectly erect near the Gulf 

 coast, instead of leaning inland as most of them do on the other side 

 of the peninsula. 



*The many patches of scrub (described farther on under soils and also 

 under vegetation) in the lake region are thought by some to represent old 

 dunes, but in many or most cases their topography seems to preclude any such 

 explanation. 



