158 FLORIDA GEOLOGICAL SURVEY-I3TH ANNUAL REPORT

hard rock and about half the land pebble is exported to Europe in normal times.*
 Since the war the business has picked up again, and several new mines have been opened in the flatwoods or pebble district, and ignore attention is being paid to the soft phosphate formerly wasted in the hard rock district. Another by-product, chiefly from the pebble
district, is a sandy rock containing too little phosphorus for fertilizing purposes, but making a pretty good road-surfacing material.t
 Limestone is probably next in importance to phosphate in our area. It has long been quarried in several places around Ocala, and recently in southeastern Citrus County. Some of it is burned for lime and some used for road material, and in a few places it has been sawed into blocks and used for chimneys, walls, etc. A variety known as coquina, composed of shell fragments rather loosely cemented together, occurs in a few places along the east coast, and has been used locally for building purposes.
 Bog iron ore is said to have been mined and smelted near Levyville in Levy County during the Civil War, for the Confederate government.
 Deposits of kaolin or porcelain clay are being worked on the south side of Lake Harris in Lake County, and brick is made at Whitney in the same county, and formerly at Brooksville and a few other places. Sandy clay suitable for road surfacing is widely distributed, particularly in the lake region.

 *The exportation of so much valuable fertilizing material has been viewed with alarm. by some writers, but it is a natural result of the normal working of the- law of supply and demand. Substantially the same arguments might be used against shipping coal, iron or lumber from states that have them to those that lack them; but if other states or countries need these things and have something of greater present value to us to offer in exchange ite is perfectly good business to make the trade. It seems to be generally true of mineral fertilizers that the soils near where they occur are pretty well supplied with that particular substance, so that they have to be transported a considerable distance to do the utmost good. By sending our phosphate to Germany, Nebraska or California in exchange for potash both sides are benefited, provided the cost of transportation, etc., is not too great.
 tFor a discussion of the Florida phosphates see papers by Dr. E. H. Sellards in our Fifth and Seventh Annual Reports, and U., S. Geological Survey Bulletin 604, by G. C. Matson (T915). The first and last of these contain many references to earlier papers, which need not be cited here.