Ohio, Brooke and Hancock counties . mooth particles thus formed are ground to dust. Before beingplaced in the cylinder the stone is carefully cleaned and weighed;after the experiment it is again cleaned and weighed together withall pieces larger than 1-16 of an inch. The difference betweenthese weighings gives the amount of dust formed and is thetest of the wearing quality of the stone. These results in Francehave been found to agree very closely with the results obtainedby many years study of the roads themselves. The French engineers have adopted a coefficient of zvear toindicate the quality
Ohio, Brooke and Hancock counties . mooth particles thus formed are ground to dust. Before beingplaced in the cylinder the stone is carefully cleaned and weighed;after the experiment it is again cleaned and weighed together withall pieces larger than 1-16 of an inch. The difference betweenthese weighings gives the amount of dust formed and is thetest of the wearing quality of the stone. These results in Francehave been found to agree very closely with the results obtainedby many years study of the roads themselves. The French engineers have adopted a coefficient of zvear toindicate the quality of the stone. They find that very few rocksin these tests form less dust than 20 grams to each kilogram ofrock, or about 2 per cent, and they adopt the number 20 as thecoefficient of the best rocks. The coefficient of other rocks is ob-tained by multiplying this number by 20, divided by the amountof dust formed per kilogram of rock, using the formula, 20x20q - -u— where q is the coefficient of wear, u the quantity of dust formed. WEST VIRGINIA GEOLOGICAL SURVEY. 297 per kilogram. The French coefficient multiplied by the per centof wear equals 40. Cementation The material for this test is runthrough a small crusher, reducing it to pieces 34 inch in size andunder. One-half kilogram of this material is placed in a ball milltogether with sufficient water to produce a stiff dough aftergrinding. The mill is given 5,000 revolutions at the rate of 30per minute, after which the dough is taken out and molded in asmall steel die, and compressed under a pressure of 1,000 briquette is about 1 inch in diameter and height. Thesebriquettes are left in air over night and placed in a hot air bath(ioo° C.) the next morning and left for four hours. They arethen tested under a one kilogram ( pounds) hammer whichstrikes a number of light blows, and the number of blows neces-sary to break the briquette is the measure of the cementing value. According to the work of the Maryla
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