Arizona republican., 1913-06-01
THE MINES OF ARIZONA

teresting facts regarding clays. shales,
 and slate.
 "Clays are ultimately derived from
 the decay Of older rocks the finer par
 ticles being carried off by streams and
 deposited along channels. in lakes. or along parts of the seacoast or sea bot tom. Tn chemical composition the cIays
 are made up essentially of silica and
 alumina. though nearly all contain more or less iron ovida and many con tain lime. magnesia. alkali, and sulphur but usually in small percentages. Shales are claYs which have become hardened by pressure The so-calIed fire clays" of the Coal Measures are shales, as are many of the other "clays" of commerce.
 Slates, SO far as origin Is concerned, are merely form of shale in which a fine, even. and parallel cleavage has 1 been developed by pressure. In com | position, therefore, they vary exactly as do the ShaIes Commercial conSidc- 1 rations in the slate industry, however give slate considerable local import ance as Portland cement material In ! preparing either roofing slate or mill ! stock for market there is enormous waste. so much material being lost n splitting, saving and dressing that only : h to 2 per cent or the rock quarried reaches the market. the remaining = ] to 90 per cent going to the dump heap. Much of this slate waste is of proper composition for use. in combination 1 with limestone. in a Portland cement i mixture, and as il is q troublesome waste product the refuse slate could be ] obtained at the cost of handling by a cement plant near 2 slate quarry. The waste slate would be serviceable 1 enough. SO far as chemical compost l tion is concerned, and could be used in i place of clay or shale in the cement | mixture. To the cement manufacturer l it would be worth as much as an equiv alent amount of clay or shaIe, but no more.
 ! The production of slate is one of the ! important lesser industries of the Unit
 ed States. In 1912 the output of slate was valued at $6,043.31S. an increase ! over 1911 of $315.299, according to A. : T Coons of the United States geolOgi- l cal survey. in an advance chapter on ! slate from Mineral Resources for ! 1912 Or this amount $4.636,1S5 rep I resented roofing slates. the production ! of which was 11972SS squares. 1 square is a sufficient number of pieces ! Of slate. large or small. to cover 100
 square feet of roof allowing for three | inch lap. It is probable therefore. that 1 the number of pieces of slate marketed 1 for this purpose ran up into the hund- ] reds of millions.
 l The roofing slate industry has shown l a general advance since the first re- | port by the geological survey in 1879,
 when the number of squares produced 1 was 361S57, valued at $1,231221, all 1 though both the output and value for 1 1912 have been exceeded several times i during the last dozen years. The rec l ord production was in 1902-1,435,1 ,16S l squares-and the greatest value was in 19O3-$5,345,078
 In 1912 there were produced 44S2,571
 school slates and 2.S9S,742 square feet ! of blackboard material. Tie value Ot
 this educational" slate was nearly $40O 0O0.
 l The author of the report discusses in l some detail the causes of the slow 1 development of the slate industry in | the United States, mentioning among other things extravagant methods of l quarrYing, including certain practices in blasting which result in large waste. and the expensive stripping method Of mining as compared with underground 1 tunneling. Mention is also made of eX- periments by the bureau of standards with a view of utilizing the top or l overburden of slate quarres for brick | making.
 1 ? Probably one of the most important
 economical devices in the slate trade
 is the machine for splitting slate. As now practiced, the making of roofing slate is nearly all done by hand by dressing gang of three men-a block l maker, splitter, and dresser. The ! mechanical device does away with the | dressing gang and makes the states, it is claimed, more rapidly. more per fectly and more economically.
 Objection to the use of the mechan- ical slate splitter has been made on the ground that some of the states are full of ribbons and other defects which would break up the slate under the ma chine. The ribbons and defects. how 1 ever, are not a condition of all slate.
 and the defective sIates would break under hand-splitting well as under the machine Another point in favor or the splitting machine is that 1t will split blocks which have become some what dry, having lost their quarry wa ter on continued exposure to the air.
 It is almost impossible to work up slate
 of this class by hand, and it has hither-
 to always found a place on the dump. A Flask is the customary unit for the measurement of quicksilver and consists of 75 pounds.