48 GEOLOGY OF THE LOTHIANS. 



cess of consolidation. Besides these appearances being ob- 

 servable in igneous rocks, when in contact with such depo- 

 sitions, they are also conspicuous in some of those plutonic 

 masses which traverse others of the same origin. In this 

 situation, however, such appearances cannot always be ex- 

 pected ; the igneous mass, which traverses one of a more an- 

 cient formation, may have been sent up before the previ- 

 ously erupted mass had cooled down, and this is rendered 

 the more likely, when we remember, that if rocks are bad 

 conductors of heat, when not far from the surface, they 

 must be much more so, when deeply seated in the globe's 

 crust. In addition to these changes in structure, there is 

 another which appears to be referable to the same cause : 

 very generally the traps associated with the coal strata be- 

 come, as they approach the strata, gradually more and more 

 felspathic, till at last they pass into a rock of compact fel- 

 spar or claystone. In some localities associated with the 

 strata which contain beds of trap, making such transitions, 

 there are similarly disposed masses of the claystone felspar. 

 In the former case the transition may be supposed to have 

 been effected by the more rapid cooling, and in the latter 

 the refrigeration may have been too quick to allow of the 

 existence of the mass as Greenstone. Some strata, when in 

 contact with these associated unstratified rocks, exhibit cha- 

 racters which, if the origin of the two classes of rocks were 

 not admitted to be perfectly distinct, might easily lead 

 the observer to consider both of contemporaneous origin. 

 Such appearances are, however, perfectly reconcilable with 

 the igneous formation of trap-rocks, and it would rather be 

 a matter of astonishment, if, in some cases, they were not 

 to be observed. By the very long continued action of heat, 

 it might be expected that both rocks would undergo a com- 

 mixture the one with the other, and that in certain places, 



