FOUND IN THE LANCASHIRE COAL FIELD. 321 



ding and joints of the stone ; the former being generally 

 supposed to be owing partly to the attraction of cohesion 

 of the particles of matter composing the stone, and partly 

 to the presence of silicate of alumina and oxide of iron, 

 which act as a cement; and the latter being produced 

 by the contraction in the bulk of the mass on desiccation— 

 an effect so well seen in clay when it is baked in the sun. 

 This would be the state of the Tock long after its first 

 elevation, until some convulsion of the earth connected 

 with the great fault, caused the vertical fissure now occupied 

 by the barytes, and displaced the bed of shale. At that 

 time, €ither from protrusion in a mass, sublimation, or some 

 other cause in which considerable heat was developed, the 

 barytes was injected into the place where it is now found. 



The walls of the vein show every indication of having 

 undergone the action of heat, portions of the sides being 

 split off and mixed with the barytes — an effect which could 

 scarcely have resulted from any other cause than the ap- 

 plication of an elevated temperature to the rock. The lines 

 of bedding, and the joints before alluded to in the lower 

 part of the walls, are nearly altogether obliterated, and 

 the sides of the rock cleave vertically. This vertical cleav- 

 age is seen in the stone for a considerable distance from the 

 vein ; but it is much stronger near the walls than elsewhere, 

 and indicates beyond all question that it has been subjected 

 to great heat, as the same effect is now known to be pro- 

 duced in flag-stones, used as hearths in iron furnaces, many 

 of which have their laminated structure converted into a 

 crystalline structure, by an alteration in the arrangement of 

 the particles composing the stone. 



The cleavage of the stone being now vertical, and parallel 

 to the direction of the vein, and not along the joints, indi- 

 cates that this structure in the mass was caused after it was 

 elevated; or else in all probability the lines would have gone 

 parallel to the joints, which are at right angles to the lines of 



