EXPLANATION OF THE MAP. 



The map of Florida herewith is reproduced from that published in Bulletin 84 of 

 the U. S. Geological Survey, by permission of the authorities of the Survey. 



It represents, approximately, the distribution of the Tertiary rocks as they would 

 appear if the superficial coating of vegetation, humus and sand was removed. Otherwise, 

 hardly anything of the geology could be represented on a map of this scale, as outcrops 

 and rock -surfaces are extremely rare in Florida, as is well known. 



It is hardly necessary to say that the outlines of the strata as delineated have not 

 been continuously followed, for this in Florida is impossible, owing to the semitropical 

 vegetation, swamps and sand by which the vast majority of the surface-area is covered. 



What has been done is this : As many observations as possible have been made, 

 along river-banks, and in every locality where any outcrop of rock could be found by dili- 

 gent inquiry or personal search with the time and means available. The results at each 

 station have been platted on a large map of the State as small spots of color corresponding 

 to the different formations. Many localities have been reached by means of correspond- 

 ence, which it was impossible for the writer to visit personally ; and the sections made and 

 specimens furnished by courteous correspondents have greatly aided in mapping the less- 

 known and accessible parts of the State. The areas thus indicated, taken in connection with 

 the topography and the known general features of structure of the peninsula, have been 

 connected by lines, and the areas thus enclosed colored accordingly. The result is an 

 approximation to the truth which in its general features is probably as accurate as can be 

 hoped for until a minute survey of the State has been completed, which will necessarily be 

 a labor of years. 



It should be stated that the observations are by no means equally distributed over 

 the whole surface of the State. The extreme northeastern portion and the region south 

 of the Caloosahatchie and east of the Kissimmee River (except the immediate sea-coast) 

 are but little known, and the same is true of the region between Sopchoppy and the Suwan- 

 nee River. On the other hand, the region between the Suwannee and Peace Creek has, 

 owing to the personal explorations of a number of geologists and the prospecting carried 

 on in search of phosphates, been quite generally and fully explored, and the general 

 distribution of the formations is likely in future to be corrected chiefly in minor details. 

 The section along the Appalachicola River is also quite thorough. In short, the map 

 represents a reconnaissance of the geology of the region for which many of the details 

 may be found in the Bulletin before referred to. 



It may be noted that in many places the limestone rock has been removed by solu- 

 tion through the action of rain-water and carbon dioxide, leaving the subjacent rocks pro- 

 truding through a covering of gravel consisting of the silicified debris of the dissolved beds. 

 In certain depressions Pliocene clays have remained undisturbed, while elsewhere removed 

 by the weather. It is to factors such as these that we owe the small patches of Eocene and 

 Pliocene which are mapped north of the main Eocene area. Doubtless there are many 

 more of these, but only those observed have been mapped ; their area being somewhat 

 exaggerated in order that they might be visible on the small scale of the map. 



To still further illustrate the structure of the peninsula, the bathymetric lines showing 

 the depths of the adjacent sea have been added to the map from the Reports of the United 

 States Coast Survey. 



The name of Alligator Creek, a Pliocene locality often referred to in the text, does 

 not appear on the map. It is the small stream entering the bay from the eastward 

 immediately below Punta Gorda. 



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