Reports & Proceedings — Geological Society of London. 137 



more particularly examined were met with in the workings of the 

 Bannock Band and Main Band Seams at Ladysmith Pit, one and 

 tliree-quarter miles south of Wellington Pit, Whitehaven. 



The pit-shaft is 1,080 feet deep, and has been sunk through the 

 St. Bees Sandstone, Gypsiferous Marls, Permian, and Whitehaven 

 Sandstone to the productive Lower Coal-measures. Splendid cliff- 

 sections of the Whitehaven Sandstone and succeeding beds, which dip 

 southwards, can be seen in a traverse of the shore from Whitehaven 

 southwards round Saltom Bay. The coal-workings have been opened 

 up south of the shaft, and therefore pass under St. Bees Head. 



The dykes certainly pass through the Bannock Band and Main 

 Band Seams and the intervening measures, which are about 54 feet 

 thick; but their full vertical extent has not been determined. 

 Their horizontal extent is variable : the longest has been traced for 

 more than a mile. They all run practically parallel one to the other 

 in a direction approximately north-north-west and south-south-east. 

 The inclination of the same dyke is not constant, but the greatest 

 deviation from the vertical was 10° south-westwards, and in general 

 the amount was very small. In only one case was a dyke found 

 associated with a small fault, the displacement being 2£ feet, and 

 even this died out in a short distance. A noticeable feature was the 

 presence of slickensiding, approximately horizontal, on the sandstone 

 surface. Flutings, simulating ripple-marks, were present on the 

 sides of the sandstone forming the dyke. 



The average width of the dykes was from 2 to 4 inches, but some- 

 times they increase to 10 inches or dwindle down to mere films. 

 Occasionally a lateral displacement was seen when the dyke passed 

 from one type of rock to another. Splitting of the dykes was 

 commonly seen. Veins of calcite and barytes traverse the dykes 

 longitudinally and transversely, while lenticles of shale and coal are 

 also of frequent occurrence in some portions of the dykes. The 

 contact of the coal and dyke substance was very sharply defined, the 

 coal preserving all the normal features even when adhering to the 

 sandstone. 



In discussing the origin of the fissures and the nature of their 

 infilling, the author draws attention to the fact that the direction of 

 the dykes at Ladysmith is that of the main system of faults in the 

 Cumberland Coalfield. These north-north-west and south-south-east 

 faults profoundly affect the Lower Coal-measures at Ladysmith Pit, 

 but do not pass up into the overlying Permian and Triassic rocks. 



An examination of the cliff-sections of Saltom Bay, where dykes 

 of the same series as those at Ladysmith Pit should emerge, shows 

 that they are not present in the Whitehaven Sandstone and suc- 

 ceeding beds. The inference was therefore drawn that they were of 

 pre- Whitehaven Sandstone age. The probable conditions which 

 obtained at the time of the formation of the fissures and their infilling 

 were as follows: The coal-seams through which the dykes pass had 

 been compressed to their present thickness, while they and the 

 associated measures were sufficiently consolidated to take a more or 

 less clean fracture. The sea in which the deltaic material of the 

 Whitehaven Sandstone was accumulating covered the area. Fractures 



