The structure of the stratified part of the earth's crust conveniently studied by the examination of a single formation--A coal-field selected for this purpose--Illustration of the principles necessary to such an investigation--The antiquities of a country of value in compiling its pre-historic annals--Geological antiquities equally valuable and more satisfactorily arranged--Order of superposition of stratified formations--Each formation contains its own suite of organic remains--The age of the boulder defined by this test from fossils--Each formation as a rule shades into the adjacent ones--Mineral substances chiefly composing the stratified rocks few in number--Not of much value in themselves as a test of age--The Mid-Lothian coal-basin--Its subdivisions--The limestone of Burdiehouse--Its fossil remains--Its probable origin--Carboniferous limestone series of Mid-Lothian--Its relation to that of England--Its organic remains totally different from those of Burdiehouse--Structure and scenery of Roman Camp Hill--Its quarries of the mountain limestone--Fossils of these quarries indicative of an ancient ocean-bed--Origin of the limestones--Similar formations still in progress--Coral-reefs and their calcareous silt--Sunset among the old quarries of Roman Camp Hill, 178 CHAPTER XI. 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, 204 CHAPTER XII.