L. C. Johnson — Phosphate Fields of Florida. 497 



following are some of its properties. u Color, — Bronze-yellow. 

 Luster, — Metallic. Form, — Cellular; the cavities being lined 

 with minute cubic crystals and the intermediate substance being 

 finely granular. Solubility, — The mineral is soluble in HN0 3 

 with separation of sulphur and a greenish yellow solution. 

 Magnetism, — On comminution about 10 per cent of the mineral 

 is found to be magnetic." The analyses are as follows. 



A, of the mixture ; B, Magnetic portion ; C, non-magnetic 

 portion ; D, after deducting insoluble and ten percent of mag- 

 netite from A and calculating to 100 per cent ; E, theory for 

 the proposed formula Fe 7 jSTiS 16 . 



A B C D E 



Xi 5-40 6-27 6-10 



Fe 42-90 66-55 40-4 41-44 40-68 



S 45-00 7-00 52-6 52-29 53-22 



Insoluble.. 4*80 



98-10 100-00 100-00 



Here it is known that the analyzed material is a mixture and 

 even if it were proved that the Sudbury pj-rite is nickeliferous, 

 to the extent indicated by analysis D, it would not be best to 

 make a new species, for certainly the replacement of a part of 

 the iron by nickel is nothing but an illustration of the common 

 law of isomorphism. 



Blueite and whartonite, therefore, like folgerite cannot be 

 recognized as distinct species. It is clear that little depend- 

 ance can be placed upon chemical formulas deduced from 

 analyses of material of such doubtful purity, especially where 

 a chief constituent is determined by difference. 



Mineralog'ical Laboratory, 

 Sheffield Scientific School, March, 1893. 



Art. LX. — Notes on the Geology of Florida : Two of the 

 lesser hut typical Phosphate Fields y* by Lawrence C. 

 Johnson, U. S. Geological Survey. 



[Presented, with the permission of the Director.] 



A. The Geology of the Gainesville Sheet — or the " Land-pebble " 

 phosphates of Eastern Alachua County. 



Commencing with Lake Santa Fe, in the north, we find it, 

 and Xunan Lake, to the southwest of it, both surrounded by a 

 flat sandy country destitute of " sinks " and of rock exposures 



* Before the Geological Society of America, Rochester, N. Y., Aug., 1892. 



