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covered by a bed of black bituminous shale of inferior oil-producing quality. The series is also characterized by numerous 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 Carboniferous 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 molluscan forms are at places found in abundance.

The Scottish Oil shales are simply beds of very fine impalpable clay shale highly impregnated with hydrocarbon, easily distinguished 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 associated. When lit with a match oil shale burns, as a rule, brightly, leaving a finely laminated skeleton of ash after all the hydrocarbon 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 neutralized 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