164 W. R. Doll— Geology of Florida. 



prin in Sarasota Bay, which were replaced b}^ a pseudomorph 

 of limonite, are of similar origin and about equal age ; although 

 I was not able to visit the locality to verify this supposition. 



The third variety I have not seen actually in formation, and 

 it has not been observed on the western coast, but occurs along 

 the upper St. John's Eiver and about Lake Monroe, where I 

 observed it in 1885. This is a sand rock in which each grain 

 is coated with a pellicle of lime, giving the mass an oolitic 

 appearance. In this rock, on Eock Island in Lake Monroe, 

 Pourtales and Wyman found the fossil remains of man which 

 created so much excitement some years ago. The rock also 

 contains recent land shells, but I observed no marine fossils. 

 Eock of this character has been formed in Florida from the 

 Miocene up, the phosphatic rock of Northern Florida is a vari- 

 ety of it, in which the limy envelope of the grains contains a 

 certain amount of phosphoric acid. 



Tertiary Mocks. 



The blanket of sand, usually overgrown with scrub palmetto 

 and cat-briars, which extends over so much of South Florida, 

 renders the task of tracing the underlying strata very difficult. 

 The sections afforded by the river banks and exposed on the sea 

 shore are usually only a few feet above the water, and in the 

 rainy season flooded, yet to these and to artesian borings the 

 observer must go for his information. There are a number of 

 rivers of reasonable size; but a wonderful absence of small 

 streams, which may almost be said not to exist except during 

 the rainy season. The soil and most of the underlying rocks 

 are so porous that at other times all moisture sinks directly 

 below the surface, or forms a marsh of greater or less extent. 

 Clay is very rare and occurs in patches of small area, generally 

 affording bones of extinct mammalia, saurians and tortoises. 

 In northwestern Florida the oolitic phosphatic rock which over- 

 lies the Orbitoides limestone is compact enough to afford a bed 

 for streams when it is continuous and forms the top rock. But 

 as soon as the edge of this rock is reached the streams sink. 

 Some notes on this formation, as reported on by Prof. E. 

 Smith, Dr. jSTeill, and members of the U. S. Geol. Survey, will 

 be found, greatly condensed, in the " Mineral Eesources of the 

 TJ. S." for 18S5, under the head of Phosphates. I may add 

 from my report of April, 1885, in regard to this rock, that 

 "from a considerable area, between the localities where it is 

 now found and the margin of the central depression or ancient 

 lake basin of northern central Florida, it has been denuded, 

 only fragments remaining scattered on the hilltops. The 

 denuding agency made gullies or channels in which clay was 

 deposited which, in its turn, has been more or less washed 



