366 REPORT OF NATIONAL MUSEUM, 1899. 



south of the outcrops of the lowest Cretaceous beds which stretch in 

 a curve from the northwest corner of the State across near Fayette, 

 Courthouse, Tuscaloosa, Centerville, and Wetumpka, to Columbus, 

 Georgia. As all the Cretaceous and Tertiary beds have a dip toward 

 the Gulf of from 25 to 40 feet to the mile, the phosphate-bearing strata 

 appear at the surface only in a comparatively narrow belt along the 

 line above indicated and are to be found only at gradually increasing 

 depths below at points to the southward. 



Phosphatic nodules and marls of the Tertiary occur in four different 

 horizons: The Black Bluffs and Nantehala groups of the Lignitic; in 

 the white limestone, and in eastern Alabama, at Ozark, in strata of the 

 Claiborne group. Selected nodules run as high as 27 per cent of 

 phosphoric acid, and marls as high as 6.7 per cent. The Tertiary is 

 not, however, regarded by Professor Smith as a promising source of 

 commercial phosphates in the State. In the Cretaceous the phosphates 

 occur in the transition beds both above and below the so-called Rotten 

 Limestone existing as nodules, shell casts, phosphatic limestones, marls, 

 and greensands. The nodules have essentially the characteristics of 

 those of South Carolina. 



The principal phosphate region of Florida, as known to-day, com- 

 prises an area extending from west of the Apalachicola River eastward 

 and southward to nearly 50 miles south of Caloosahatchee River, as 

 shown on the accompanying map. 1 According to Mr. Eldridge, the 

 deposits comprise four distinct and widely different classes of commer- 

 cial phosphates, each having a peculiar genesis, a peculiar form of 

 deposit, and chemical and physical properties such as readily distin- 

 guish it from any of the others. 



According to their predominant characteristics or modes of occur- 

 rence, these classes have come to be known as hard-rock phosphates, 

 soft phosphate, land pebble or matrix rock, and river pebble. With 

 the exception of the soft phosphates, they underlie distinct regions, 

 each class being separate or but slightly commingling with one another. 

 The type of the hard-rock phosphate, as described by Mr. Eldridge, is 

 a hard, massive, close-textured homogeneous, light-gray rock, showing 

 large and small irregular cavities, which are usually lined with second- 

 ary mammillary incrustations of phosphate of lime (Specimens Nos. 

 66737, 66741, U.S.N.M.), the general appearance being that of the 

 calcareous deposits of the preglacial hot springs of the Yellowstone 

 National Park. 



There are numerous variations in color and physical characteristics 

 from this type, but which can best be comprehended by a study of 

 the collection. This type carries some 36.65 per cent phosphoric 

 anhydride (P 2 O 5 ). The deposits of the hard-rock phosphate lie in 

 Eocene and Miocene strata, occurring in the first named as a bowlder 



1 Preliminary sketch of Phosphates of Florida, by George H. Eldridge. 



