heat, pressure and moisture, and result in the formation of hydro-silicates of calcium and magnesium.

The sand used in the manufacture of sand-lime brick should be comparatively pure and preferably with some variation in the size of the grains. The mixture of lime, sand, and water, is cut out in the form of bricks and conveyed to a hardening cylinder. Necessary heat and pressure is obtained in the hardening cylinder adapted for the purpose. The sand-lime bricks are placed in this cylinder and subjected to a pressure and temperature which varies according to the method of treatment. With a pressure of about two atmospheres and a temperature of 125 degrees C. the duration of exposure in the cylinder should be about seventy-two hours. With a steam pressure of seven to ten atmospheres and 170 to 175 C, six to ten hours' exposure is usually sufficient.

CONCRETE BUILDING BLOCKS, HOLLOW BLOCKS, OR ARTIFICIAL STONE.

The materials for the manufacture of concrete building blocks are sand, gravel, or crushed stone, and cement. The sand intended for use in making cement blocks should be sharp and angular. Coarse grained sand is preferred to fine grained. A mixture of coarse and fine grained sand, however, gives excellent results, and requires less cement, since the relative proportion of voids in the sand is reduced by the presence of the fine grains of sand among the coarse. It has been commonly supposed that a clean sand must be used, but recent experiments seem to indicate that a small proportion of loam or clay is not detrimental. Tests carried on at the Ohio State University appear to indicate that clay or loam up to 15 per cent of the weight of the sand adds strength to a mortar.*

Concrete building blocks have been, as a rule, favorably received throughout the State. The ease of manufacture, together with the relatively small cost of equipment and

*Bulletin No. 2, 4th Series, Ohio Geol. Survey. P. 33, 1904.

the abundance of sand is greatly in favor of this industry. Most cities of considerable size have one or more firms engaged in the manufacture of this material. Sand suitable for the manufacture of concrete building blocks occurs in almost all parts of the State.

MINERALS NEW TO THE STATE.

SULPHUR.

Native sulphur has been found in Florida during the past year, a large mass estimated to weigh two tons having been brought up from the pit of the Dutton Phosphate Company, at Floral City. The phosphate at this place was worked down to the water level as a dry pit and is now being worked below the water level by dredging. The mass of sulphur was brought up on the dipper from about thirty feet below the water level, or a total depth from the original surface of about seventy feet. When first brought up the sulphur mass was mistaken for a rock boulder, which being too large to go through the dipper, was drilled into and blasted. Most of the pieces fell back into the pit, a few thrown on the land were found to be crystallized sulphur with only a slight admixture of impurities. The phosphate beds of Citrus County rest upon Lower Oligocene limestone. The sulphur was found either upon or in Oligocene limestone.

PROBABLE SOURCE OF SULPHUR.

In a Bulletin on the Water Supply which accompanies this report the writer has discussed in some detail the probable source of hydrogen sulphide in underground waters. It is there shown that the hydrogen sulphide in underground water is supplied not from deposits of native sulphur, but from decaying organic matter and from sulphides and sulphates contained in the rock. It is also shown that hydrogen sulphide, while not originating from

sulphur deposits may itself, under proper conditions, form such deposits. This gas, although not affected by oxygen when dry is, under moist conditions, or in the presence of water containing oxygen in solution slowly oxidized, forming sulphur and water.

In view of these facts, it seems probable that the sulphur mass found at Floral City was formed by the decomposition of hydrogen sulphide gas slowly escaping from the underground waters, the reaction taking place in the presence of a limited supply of oxygen.

While only a small quantity of sulphur has been found in Florida, if the above suggestion as to the origin is correct, the presence of this mineral in workable quantities is not impossible and is indeed even probable.

MINERAL WATERS.

The springs of Florida are famous for their volume of flow as well as for the clearness and beauty of their water and the beautiful scenery about them. Many of these springs are used as health resorts. The United States Geological Survey volume on Mineral Resources reports the sale of mineral waters in Florida for 1907 as 43,430 gallons, valued at $12.378.

The areas in which flowing artesian wells are obtained are indicated on the map which accompanies Bulletin No. 1 of the Florida Survey.