232 L. C. Johnson — Structure of Florida. 



to it in 1881 by Dr. Eugene A. Smith, — that it is of the upper 

 Eocene, known as the Yicksburg stage. Confirming this de- 

 termination was the opinion of Dr. Eugene W. Hilgard, and of 

 Mr. Angelo Heilprin, who judged by the fossils submitted to 

 them. The latter however, as I understand him, now ex- 

 presses doubt, whether the true Yicksburg rock with Oroi- 

 toides Mantelli really belongs to these Florida localities. It 

 seems he has seen specimens of a superficial formation found 

 in many places, from as far south as Pemberton Ferry to as far 

 west as Wakulla County, wanting, so far as he has observed, 

 in Oroitoides Mantelli, but having two others, 0. ephippium 

 and 0. dispansa, and sometimes associated with a foraminifer 

 which he says is Opercidina complanata, and with a Hemiaster. 



Such rocks do seem in many places, especially toward the 

 south, to constitute a thin upper layer, and always more or less 

 silicified. There is no sufficient reason as yet observed, to 

 regard it as more than an upper layer — similar to such super- 

 added layers seen in Alabama at the Lower Salt Works on the 

 Tombigbee Hiver, described in Bulletin 43 of the U. S. Geo- 

 logical Survey. 



Possibly these irregular deposits may be remnants of the 

 Nummulitic limestone, which is really a stratum overlying the 

 Yicksburg rocks, well seen at the old iron works near Levy- 

 ville, Levy County At Levyville it is a beautiful soft porous 

 building stone, about twenty feet in thickness, which was util- 

 ized in the erection of the Confederate iron- works. Often 

 struck in the artesian borings and easily identified by the 

 peculiar nummulites, it has a greater thickness under the Neo- 

 cene formations to the east. In these western regions at has 

 probably suffered general removal by erosion. 



Apparently conformable in deposition with the Yicksburg 

 stage the Levyville formation is evidently not identical with 

 it; and demands a further investigation. It is a mistake how- 

 ever to suppose that this Nummulitic formation everywhere 

 hides the Yicksburg rocks of the Oroitoides Mantelli, or ever 

 did overlie the whole of it. Numerous are the exposures to 

 prove the contrary. In very many places, especially in Alachua 

 county and northward, the outcrops cannot be distinguished 

 from the rocks of Yicksburg and of the Chickasawhay, Missis- 

 sippi. Not often is it sufficiently exposed to the action of 

 water percolating directly through the surface sands, to become 

 silicified. Yet there are places where even this has occurred ; 

 notably at Payne's pi*airie. 



Often therefore, it is quite a rotten limestone, — affording 

 opportunity by its solution for the excavation of those under- 

 ground passages for water, amounting sometimes to rivers, — 

 which is one of the phenomena of Florida. The " Natural 



