246 THE JOURNAL OF GEOLOGY. 



covered by a bed of black bituminous shale of inferior oil- 

 producing quality. The series is also characterized by numer- 

 ous well-marked beds of unfossilferous red, green and gray 

 marl, the origin of which is not very clear, but as the marl is 

 seen at places to contain pieces of felspathic volcanic ash, it 

 seems reasonable to suppose that it may be made up in part at 

 least of impalpable mud derived either from volcanic dust or 

 from the disintegration of some old volcanic area which has now 

 disappeared from view, but which formed part of the ancient 

 mainland from which the other sediments were derived. There 

 is no distinct evidence of volcanic action during the greater part 

 of the Oil shale period in the Lothians, and the numerous ash 

 necks which pierce the strata were probably connected with the 

 extensive outbursts which took place during the subsequent Car- 

 boniferous Limestone period. Many beds of gray and yellow 

 sandstone are found interbedded with the oil shales as well as 

 impure coals, fire clays, and non-bituminous carbonaceous shales 

 — the "blaes" of the Scottish mines, in which plant remains, and 

 fresh-water moUuscan forms are at places found in abundance. 

 The Scottish Oil shales are simply beds of very fine impalpa- 

 ble clay shale highly impregnated with hydrocarbon, easily dis- 

 tinguished in the field by their resistance to the disintegrating 

 action of the weather, thin brown streak, and the facility with 

 which they can be cut and curled up with a sharp knife. The 

 texture is at times tough, almost leathery, and thin pieces are 

 slightly flexible and easily distinguishable from ordinary black 

 carbonaceous "blaes" with which they are often closely asso- 

 ciated. When lit with a match oil shale burns, as a rule, brightly, 

 leaving a finely laminated skeleton of ash after all the hydrocar- 

 bon has been exhausted. On distillation the yield of oil varies. 

 Good shales should give, per ton, at least thirty gallons of crude 

 petroleum, as well as enough ammonia to produce, when neu- 

 tralized with sulphuric acid, from ten to fifty pounds of sulphate 

 of ammonia. This product is often as valuable as the oil, and 

 much skill has been employed in the construction of retorts to 

 extract it completely. The crude oil when refined gives various 



