Page:The Journal of geology (IA journalofgeology21894univers).pdf/261

products, such as tar, naphtha, paraffin, light illuminating and heavy lubricating oils, and the oil industry of the Lothians was for more than a quarter of a century a source of great profit and employment to the capitalists and operatives of the district, but of late years the severe competition with foreign producers has made most of the works quite unremunerative. The thickness of the oil shale beds varies considerably from place to place, and it is quite common to find a good seam thinning out in one district and passing into ordinary carbonaceous shale, or disappearing altogether, while another seam above or below it may improve in quality in proportion as the first deteriorates. The Broxburn shale—the richest seam in the Broxburn district—varies in thickness from about two and a half to eight feet, and the Dunnet shale reaches at places a workable thickness of thirteen feet.

An interesting phenomenon is observable at some places where the strata have been heated by igneous intrusions. In these cases if an oil shale bed has been affected by the heat, partial distillation has followed, and the surrounding rocks, including the eruptive sheet itself, have become impregnated with the hydrocarbonaceous ingredients expelled from the shales. In a recent diamond boring a core of the eruptive dolerite was brought up from a depth of over 600 feet, traversed by veins of solid paraffin, which melted when the rock was laid in the sun, and at the outcrop of this intrusive sheet it is found to contain cavities filled with tarry matter and to give off a strong bituminous odor when freshly broken with the hammer. This eruptive sheet has forced its way for miles through strata adjoining the Broxburn shale, and whenever it has touched or even approached the shale the seam has of course become quite worthless economically. The well-known sandstone of Binney, which is located some fathoms below the Broxburn shale, has long been known to contain veins of ozocerite or an allied hydrocarbon, and the quarrymen used formely, when the rock was extensively worked for building and monumental purposes, to make black candles of the substance, some