ase, at present, being for ocomotives and factory-engines; it sells in the market at about the price of Scotch coal, being usually about 2s. less than Newcastle coal. The output in 1881 is by far the largest ever reported, though this coal has been mined since 1797. Two seams have been worked, one at a depth varying, according to a regular dip, from 30 to 60 metres (334 to 66 yards), TABLE LIV.-Statement showing the Domestic Exports of Coal from the several Custom Districts of the United States for the years ended June 30, 1880 and 1881. [Specially furnished by the U. S. Census Bureau.] and 15 to 44 centimetres (6 to 1. inches) thick, and the other 24 metres (nearly 79 feet) lower, 142 metres (4 feet 8 inches) thick. Swedish engineers acknowledge that they are not thoroughly acquainted with the ex tent of this coal-formation, though numerous bore-holes have been put down and shafts sunk. The measures contain coal of inferior quality, as well as fire-clay. 392,626 1,362,901 222,634 695,179 ports, shown in Table LIV., exhibits the fact that the States. Coal, value. Duties. Per cent. Iron, value. Duties. Per cent. The relative values and quantities of the exports from and the imports to the United States of anthracite and bituminous coal are shown in Table LVI. In comparison with these are given the exports and imports of iron ore and manufactures of iron. In coal the total value of exports is but little less than the value of imports, while in iron and iron ore the excess of imports over exports is very great. This table shows very plainly the distribution according to the various countries. The United States obtains its principal imports of coal from England (gas coal) and Nova Scotia, which supplies some of the extreme Eastern points, while British Columbia FIRE-CLAYS OF THE COAL-MEASURES. and Australia furnish their coal to San Francisco and the Fire-clays may be looked upon as a special term for extreme Western ports. The statement of domestic ex- the gray clays of the coal-measures, interstratified with. $2,073,954-78 $516,006-95 24-09 $32,991,038 45 $12,115,096-22 86-07 TABLE LVI.—Imports and Exports of Coal, Iron Ore, and Iron to and from the United States, 1880–1881. and generally in close proximity to, the seams of coal, in beds varying from a few inches to many feet in thick ness. They are locally known as "clunches" and under-clays," and are supposed to represent the soil that produced the vegetation from which the coal was formed. The association of coal with the fire-clays of the Carboniferous formation has localized the manufacture of fire-bricks, and by far the larger proportion are produced in the coal-measure districts. The fire-clays of the coal-measures vary as regards their refractory character, not only in the different coal-fields, but the individual strata in close alternation often present sudden variations, refractory beds being interstratified with useless strata largely charged with disseminated carbonate of iron. The gray color of the coal-measure clays is largely due to the presence of this mineral. The average contraction of the coalmeasure fire-clay is a little over 2 per cent. The importance of these clays in England may be realized from the fact that in 1880 they produced. 3,062,544 tons, valued at £1,635,650. The product consists of fire-clays, potter's clay, china clay, and stone. Prof. J. P. Lesley, State geologist of Pennsylvania, gives his theory of the formation of fire-clay as follows: "The thick and valuable deporit described and repeatedly alluded to in this report as underlying the Kittanning coal is but one of a number of such in other parts of the Appalachian coal-fields, equally stimulating to the curiosity of the geologist. Since Sir W. E. Logan first published the fact that every true coal-bed has its underclay, efforts have been made to explain its cause, but not with entire success. I make the following suggestion: A peat-bog, and still more truly a lake, invaded on all sides by sphagnous vegetation, must have a water-circulation set up by evaporation from the central surface and by percolation from the surrounding land. But this circulation must be feeble, capable of carrying only the finest mud. In the course of ages the amount of clay-all of it fine, and all of it of one kind-thus abstracted from the dry ground and transferred to the peat-filling hollows, must be very large. The dry grounds are chiefly a mixture of fine gravel, rounded grains of quartz, and rounded grains of feldspar. The pebbles and sand are not soluble; the feldspar is. The former remain behind; the latter follows the in-draft, and settles beneath the evaporating surface through and beneath the floating pea. If FIG. 37.-Diamond Drill. |