FOUND IN THE LANCASHIRE COAL FIELD. 123 



this view wasconfirmed by the occurrence, in several instances, 

 of veins or rather lamina of oxide of iron, or oxide of 

 copper, according to the manner in which the experiments 

 were conducted." 



Some years since. Sir John Herschel, in speaking of cleav- 

 age, suggested, that if rocks have been so heated as to allow 

 a commencement of crystallization; that is to say, if they 

 have been heated to a point at which the particles can be- 

 gin to move amongst themselves, or at least on their own 

 axes, some general law must then determine the position in 

 which these particles will rest on cooling. Probably that 

 position Avill have some relation to the direction in which 

 the heat escapes. Now, when all, or a majority of particles 

 of the same nature, have a general tendency to one position, 

 that must of course determine the cleavage plane. The 

 above views the author of this paper has seen verified in 

 many instances where laminated shales and sandstones have 

 been thrown out of a coal mine, and deposited without any 

 order one upon another, and, with the small coal mixed 

 with them, set on fire, and subjected to great heat. This 

 mass, after it has been acted upon by sufficient heat, when 

 cooled shows a cleavage sometimes very regular in form, and 

 at other times of a more imperfect structure. But the planes 

 of the cleavage lines are not at right angles to the original 

 planes of deposition, as we should find in baked clay or mud 

 dried in the sun, but at right angles with the cooling surface. 

 Thus laminated shales, which have been placed perfectly 

 level, in an oblique direction, or on their edges, have all 

 the same vertical cleavage, provided the cooling surface be 

 in one and the same direction. 



In the case of the vein described in the present com- 

 munication, the sandstone rock in which it occurs appears 

 to have been elevated to the position of the general dip 

 of the quarry, which is to the N.W., and probably remained 

 in that position for a long period of time. The great S.E. 



