OIL SHALES— SCOl^TISH CARBONIFEROUS SYSTEM. 247 



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, trav- 

 ersed 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 ozoce- 

 rite or an allied hydrocarbon, and the quarrymen used formerly, 

 when the rock was extensively worked for building and monu- 

 mental purposes, to make black candles of the substance, some 



