Page:Popular Science Monthly Volume 27.djvu/548

530 marvelous stories of its penetrating powers. They have been known to assert that, if an empty and hermetically sealed glass bottle be placed within the sheds where such stones are being cut, it will shortly be found with a fine white deposit of the dust upon the bottom and on the inside, and no argument can convince them that it came there otherwise than through the pores of the seemingly impervious glass!

The quarrying of slate for roofing purposes is an industry of comparatively recent origin in the United States, few of the quarries having been operated for a longer period than twenty or thirty years. The earliest opened and systematically worked are believed to have been those at West Bangor, Pennsylvania, which date back to 1835. The abundance of slate tombstones in many of our old churchyards, however, would seem to prove that for other purposes than roofing these stones have been quarried from a much earlier period. It is stated, moreover, that as early as 1721 a cargo of twenty tons of split slate was brought into Boston from Hangman's Island in Braintree Bay, which may have been used wholly or in part for roofing purposes; but the greater part of the material for this purpose was imported directly from Wales. It is interesting to note, in this connection, that, daring the business depression of 1876-'80, almost the entire product of the American quarries was exported to England, where it sold for even less than the Welsh slates, though necessarily at very small profits. The return of more prosperous times, however, created a local demand, and the export trade has been largely decreased accordingly, though considerable quantities are still sent out to the West Indies, South America, England, Germany, and even New Zealand and Australia.

At present not far from $3,328,150 are invested in the slate-quarries of the United States, and the value of the annual product is some $1,529,985.

Pennsylvania is the leading State in this industry, her quarries being located in Lehigh, Northampton, and York Counties, in the eastern part of the State. These slates are all blue-black in color; as are also those from Maine, Massachusetts, and Maryland. The Vermont slates are of a greenish or purple color, while those of New York are mostly purple and red, the latter color being found in extensive deposits near Granville, in Washington County.

Besides for roofing purposes, slates are used for billiard-tables, mantels, floor-tiles, flagging, and in the manufacture of school-slates. For the last-named purpose a soft, even-grained stone is required, and almost the entire supply is at present brought from Pennsylvania and Vermont.

Of late years, the business of marbleizing slates for mantels and fireplaces has become an important industry. All kinds of stones can be imitated by this process, but that most commonly seen is the green verd-antique marble and the variegated marbles of Tennessee. Like