I.—Introduction The theory generally accepted as explaining the occurrence of Coal Measures in detached basins is that after the deposition of these rocks a series of earth movements, post-Carboniferous in time, took place, certain ridges were upheaved, and after these had suffered denudation the remaining portions of the Coal Measures would survive in the basin-like depressions formed by the upheaved margins. Of late years, however, evidence has been accumulating which seems to suggest that the older theory does not accurately represent the complicated series of earth-movements that were in progress during Carboniferous times, nor the part they played in determining the present limits of the British coalfields. In this paper it is proposed to briefly discuss the effects of these movements so far as the Yorkshire, Derbyshire, and Nottinghamshire coalfield is concerned, and to determine, so far as is possible, their sequence and character. For the sake of brevity the area under discussion will be called the Yorkshire coalfield. II.—The pre-Carboniferous Floor under Stress If we knew more about the structure of the old Silurian floor it is very possible that we should find the present form of the coal basins indicated, and that in no very vague form either. When its various beds were subjected to the tangential stress that marked the post-Silurian era, the stressed rocks found relief in plication and fracture, with the resulting formation of its characteristic ridges and hollows. When equilibrium had been established, it is clear that the more normal phase of ...