DIP OF THE STRATA NEAR EDINBURGH. 69 



The rocks around Edinburgh, and in the adjoining parts 

 of Fifeshire, thus appear to exhibit a certain tendency to a 

 concentric disposition. When, however, the whole district 

 is examined, there is far from being visible that symme- 

 trical aspect which characterizes a locality where the vari- 

 ous mineral masses, whether aqueous or igneous, have been 

 tilted up around an axis ; but, on the contrary, the nume- 

 rous instances which occur of strata, within the area of this 

 somewhat mantle-shaped stratification, dipping to points 

 in accordance with the supposition that an anticlinal ele- 

 vating force had operated, render it probable that the ap- 

 pearances indicative of such an action are merely acciden- 

 tal. The Castle rock is a point from which many of the 

 rocks dip, but if it had exerted an influence over so great 

 a space, the sandstone which in many places, as at the 

 Grange and Burntsfield, has a northerly dip, ought to 

 plunge to the south, while many other strata, dipping to 

 N. W., as those of Colinton, Slateford, and Craig-Lock- 

 hart, ought to sink to the S. W. 



Concerning the mode by which these Plutonic and Neptu- 

 nian rocks have assumed their present position, it may be 

 difficult to conjecture; it must, however, either have been con- 

 temporaneous with the formation of the former class of rocks, 

 or subsequent to that of both. If it is affirmed that the ar- 

 rangement which the Plutonic rocks of this district exhibits is 

 original, it may be no easy matter to explain Jiow trap could 

 be erupted, so as to overhang valleys without flowing into 

 them ; but, still, there certainly appears little reason to be- 

 lieve that the causes which have made the trap-rocks in the 

 neighbourhood of Edinburgh to assume their existing ap- 

 pearances, have been others than those which arranged the 

 alternations of trap-rock which constitute, in many districts, 

 mountain masses. When such beds are inclined, thev have 



