CHAPTER XI.. Intercalation of Coal Seams Among Mountain Limestone Beds of

Intercalation of coal seams among mountain limestone beds of Mid-Lothian--North Greens seam--Most of our coal seams indicate former land-surfaces--Origin of coal a debated question--Erect fossil trees in coal-measures--Deductions to be drawn therefrom--Difference between the mountain limestone of Scotland and that of England--Coal-bearing character of the northern series--Divisions of the Mid-Lothian coal-field--The Edge coals--Their origin illustrated by the growth of modern deltas--Delta of the Nile--Of the Mississippi--Of the Ganges--Progress of formation of the Edge coals--Scenery of the period like that of modern deltas--Calculations of the time required for the growth of a coal-field--Why of doubtful value--Roslyn Sandstone group--Affords proofs of a general and more rapid subsidence beneath the sea--Its great continuity--Probable origin--Flat coals--Similar in origin to the Edge coals below--Their series not now complete--Recapitulation of the general changes indicated by the Mid-Lothian coal-field,

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