424 Proceedings of the British Association. 



joint goes through limestone and shale, the opening is wider in the 

 limestone, narrower in the shale. 



3. Fissures which go through a great variety of strata, though 

 very different, as sandstone, limestone, shale, &c. Viewing the mat- 

 ter on a horizontal plane, we find the divisions to be generally ar- 

 ranged in parallel lines. This is well seen in the vast limestone 

 scars which begird the mountains of Yorkshire ; certain of these, 

 which may be called master-joints, are seen to be much more regu- 

 lar than the other joints, sometimes empty to an immense depth, 

 sometimes filled by clay, holding a great proportion of pebbles. 

 The sides ai*e sometimes lined by calcareous spar and sulphate of 

 barytes, &c., and in some cases the deposition of calcareous spar has 

 gone to such an extent, that the whole cavity is filled with it. If 

 a bed of shale is interposed between beds of limestone, the fissure 

 is much wider in the limestone than in the shale. Carbonate of 

 copper, oxide of iron, and other substances, also occur in the joints. 

 A certain direction of the joints is common to the slate, to the lime- 

 stone, to the carboniferous series, and even to the oolitic rocks of 

 the north of England. Through the whole of the country examined 

 by Mr Phillips between the Tees and the south of Yorkshire, there 

 is the most general agreement, the direction of nearly all the mas- 

 ter joints being to the NN. W., which is now the direction of the 

 magnetic needle. Some general and long continued cause appears 

 to have been in operation, which has produced this constancy of 

 direction. Other joints very extensive, but less so than those rang- 

 ing NN. W., belong also to the division of master-joints. 



In mineral veins in the north of England, a direction passing 

 from the east, but a little to the north of it, is tTie most common. 

 The miners call these right running veins. Other veins and rock 

 dykes and faults occasionally cross them, and these generally coin- 

 cide with the direction of the great master-joints. There is in one 

 part of Yorkshire an immense quantity of basalt. The metallic veins 

 pass nearly east and west through this, as they do through sand- 

 stones, limestones, shales, &c. Other portions (connected in the 

 opinion of Professor Sedgwick with this great mass) go off from it 

 in directions so nearly straight, that a surveyor might use them as 

 lines for the basis of his operations. 



There is an analogy between the direction of the great mineral 

 fissures and the lines of convulsive movement in the north of Eng- 

 land. There is a general line of dislocation north by west, from 

 which passes another to the east, and another to the west south- 



