GEOLOGY. 35 



Scotland — by large outliers and masses of ore found on the 

 surface of the ground. Some of these are described as weigh- 

 ing from ten to twenty-four stones in weight. A vein was 

 opened about two feet thick, and gradually decreased from 

 seven to about three inches, when, by the disturbed and rup- 

 tured state of the strata, and frequent intrusion of the trap, 

 the operations were abandoned as being unremunerative. The 

 shaft, which is still open, was carried through the trappean 

 rock ; and thus the position of the vein gives probability to 

 the theory that the igneous agency which forced upward the 

 trap, produced also by sublimation the ore which is found 

 enclosed within its mass or near vicinity. 



Trap Dykes, composed of concretionary greenstone and 

 basalt, occur frequently in the neighbourhood, and, indeed, are 

 everywhere distributed over the coal-basin. They range in all 

 directions, rising perpendicularly through the stratified rocks, 

 and often stand several feet above the strata, like a wall 

 rudely piled up by Cyclopean builders. The adjacent strata 

 in the line of their direction are generally altered in position, 

 upheaved or thrown down by faults, and their structural char- 

 acters are much changed. The coal for some distance is 

 calcined and valueless ; the limestone near them will not burn 

 into quick-lime ; and the shales and sandstones are hardened 

 and chertified. The transference of mineral qualities is likewise 

 remarkable in the intruding trap itself, which at the point of 

 contact becomes more or less calcareous and siliceous — often 

 coated with iron, and enclosing portions of coal or carbon. 

 These changes resulted clearly from the igneous agency, which 

 by its upward pressure severed the superincumbent mass of 

 stratified rocks, and then poured like molten lead its subterra- 

 nean materials into the fissures. Once observed in any district, 

 these natural d^d^ies are of too marked a character not to excite 

 inquiries, in every intelligent observer, as to their uses and 

 mode of formation ; and occurring, as they do, in every region, 



