Commercial operation would, of course, require underground mining by some procedure such as the room-and-pillar mining technique developed by the United States Bureau of Mines. The Bureau's excellent work in the development of oil shale mining methods was initiated by the enactment of the Synthetic Liquid Fuels Act of 1944. In the room-and-pillar method, the mine roof is supported by pillars of oil shale, left standing at staggered intervals. This room-andpillar mining method recovers about 75 percent of the available Mahogany ledge shale, and permits a substantial reduction in the cost of mining shale because it affords the use of giant mining and transportation machinery. There are, however, risk factors inherent in the mining of oil shale that act as deterrents to profitability of operation. Experience has shown that shale formations do not exist as uniformly solid strata. In any commercial oil shale venture, it would be necessary to explore each potential mine site extensively by the use

of diamond drilling. Closely spaced drilling patterns would be required to outline the reserves and to then, more specifically, block out possible mine locations. The diamond-drilling technique makes it possible to locate voids during this exploratory program. On the basis of information gained during this exploration, a given site will be developed or abandoned. In spite of this exploration, however, it is still possible to run into unpredicted joints and/or faults after opening up a mine, which would present a safety hazard that could make mining impossible and force abandonment of the selected area. Such a joint system in the Bureau of Mines mine at Rifle, Colo., is thought to have caused their roof fall in 1955. It is also significant that oil shale is about four times as resistant to breaking as concrete, and therefore exploration is costly. The risk, then, is great even when the best mining technique now known (room-and-pillar) is used, in that there is no certainty an established shale mining operation can continue if an unsafe or low quality section is encountered. Nevertheless, the commercial production of strategically important shale oil requires that these risks be met and ways found to minimize them. It is our conviction, and the belief of recognized mining experts, that as more individuals and firms are attracted to the mining of shale and the production of shale oil, great strides in mining technology will be achieved. This advanced technology

may permit the eventual production from more marginal oil shale deposits such as the "Chattanooga formation" in Tennessee.

Whatever mining technique is used, oil shale is drilled, blasted, and the resultant broken material transported first to the crushing plant (figs. 7, 8, and 9).

Because of the advances which have already been made in oil shale mining, the spotlight has been thrown on the quest for a process technique for extracting shale oil from oil shale rock. Shale oil is extracted by an "ordinary treatment process" which we refer to as "retorting," and which is seen, by way of analogy, to be substantially equivalent to the furnacing of quicksilver ores,' as in the following:

In the treatment of the ore (oil shale or cinnabar), the ore is passed vertically through a retort or furnace in which a countercurrent stream of hot gas acts as a heat exchange fluid to increase the temperature of the ore and thus decompose the product-containing compounds (kerogen or mercuric sulfide) present. This thermal decomposition causes the kerogen or mercuric sulfide in the ore to change from a solid to a gas or vapor. The products of thermal decomposition are: A vaporized liquid product (oil or mercury); materials which are normally

gaseous at room temperature; and residual spent material. In the vapor state the products of decomposition flow from within the individual pieces of ore. The vaporized liquid product (shale oil or mercury) is condensed and collected as a liquid and, in the case of oil shale, the normally gaseous material is a combustible product of low B. t. u. content.

As far as the refining of shale oil into competitive petroleum products is concerned, recently completed experimental refining confirms that all major problem areas are resolved.

Finished products derived from shale are indistinguishable from their natural petroleum counterparts, just as sugar from beets is indistinguishable chemically from that made from cane.

Shale-derived end products include gasoline, diesel fuel, and jet fuel. I am happy to be able to tell you that barrel quantities of specification JP-4 jet fuel and submarine diesel fuel are now en route for engine testing by the United States Navy.

In conclusion, it seems self-evident to me that, because the rock itself has no value, a depletion allowance, to mean anything, must be on the basis of the extracted oil itself, not on the rock. Your favorable action providing equitable tax treatment for this potential industry, based on new American technology, will help assure a continued, reliable source of petroleum for the citizens and armed services of this country.

Further reference is made to appendix C-bibliography of articles describing ordinary cinnabar treatment processes, and United States patents describing retorts applicable to both oil shale and cinnabar ore.

APPENDIX A

DEFINITION FROM METALLURGICAL DICTIONARY, BY J. G. HENDERSON, PUBLISHED BY REIN HOLD, 1953

Concentrate: The product obtained by concentrating disseminated or lean ores by mechanical or other processes, thereby eliminating undesirable minerals or other constituents.

Furnace: A high-temperature industrial heating device for the processing or reduction of ores; for the heat treatment, processing, or melting of metals; for the firing of ceramic ware or refractories; and for other heating applications. Basically, a furnace consists of a heat-resistant enclosure (usually refractory lined), and an internal source of heat which may be the combustion of fuel or some adaptation of electrical heat energy, such as electric arc. There is in existence a wide variety of industrial furnaces. Some are classified with respect to structural design features, or the class of work accomplished; some for the material or products treated, converted, or otherwise processed; some for the heat source utilized, while many are named for the designer, inventor, or manufacturer.

Gangue: The waste portion of ore from smelting or refining operations. Mercury: A metallic element; atomic weight, 200.6; atomic number, 80; melting point, -38° F.; boiling point, 675° F.; valence, 1 or 2; specific gravity, 13.6. Mercury is a heavy, liquid metal, silvery, and a fair conductor of heat and electricity. Mercury dissolves certain other metals to form amalgams. It is occasionally found in the native state, but its chief source is the ore cinnabar, a sulfide of mercury. Mercury is used for silvering mirrors; for barometers, thermometers, and other scientific instruments; for mercury discharge lamps, and in making dental amalgams. Considerable quantities are used in the amalgamation process for the recovery of gold and silver from their ores.

Ore: A naturally occurring substance containing minerals that can be extracted profitably.

Retort: Any vessel used for the distillation of volatile materials. Retorts are commonly used in process metallurgy for the distillation and subsequent recovery of either the distillate or the residue of metal compounds.

Roasting: Any heating operation for the purpose of driving off volatile materials, or to effect certain chemical changes at temperatures below those required for complete fusion. As a process metallurgical operation, it consists of heating ores under oxidizing conditions, usually for the purpose of removing sulfur from sulfide ores, or to convert such ores to sulfate.

Sintering: (1) The formation of larger particles, cakes, or masses from small particles or grains by heating alone, or by heating and pressing, so that certain constituents of the particles or grains coalesce, fuse, or otherwise bond together. See also Coalescence; Fritting. (2) In powder metallurgy, the heating of metal powders or compacts to convert them into coalseced, alloyed brazed, or welded masses, under controlled conditions of time, temperature, and atmosphere. Smelting: A process metallurgical operation in which the metal sought is separated in a fused state, from the impurities with which it may be chemically combined or physically mixed.

DEFINITIONS FROM WEBSTER'S NEW COLLEGIATE DICTIONARY, SECOND EDITION Cinnabar: Red mercuric sulfide, Hg, the only important ore of mercury. Artificial red mercuric sulfide, used principally as a pigment. The color, vermilion. Concentrate: To bring or come to, or direct toward, a common center; to gather into one body, mass, or force; as, to concentrate rays to a focus; to concentrate attention. To increase in strength by removing diluting or admixed material; as, to concentrate ores by washing; a concentrated food.