ST LEONARD'S HILL. 51 



natural arrangement, but, on the contrary, will describe 

 separately the geology of the counties of Edinburgh, Had- 

 dington, and Linlithgow. 



Mid- Lothian, like the other counties, contains both class- 

 es of unstratified rocks, viz. the augitic and felspathic. The 

 former constitutes various hills, while in the Pentlands the 

 latter rises into mountain masses of greater or less height. 

 The principal trap formations of Mid -Lothian occur within 

 a circuit of nine miles round Edinburgh. Immediately to 

 the east of the city the hills of Salisbury Crags and Arthur's 

 Seat rise to the heights of 550 and 8&# feet above the level 

 of the Firth of Forth. The splendid geological appear- 

 ances which these hills exhibit render an examination of 

 them interesting in the highest degree, and few points can 

 be mentioned which, within the same compass, present so 

 many beautiful and instructive illustrations of the Plutonic 

 origin of trap rocks. Salisbury Crags and St Leonard's 

 HilJ, which may almost be considered as constituting one 

 hill, are each formed of a mass of trap, surmounting and 

 rising through the slates and sandstone of the coal-forma- 

 tion. The igneous portions of these hills appear to have 

 been produced by the intrusion of masses of trap, parallel 

 to the strata, and forming lateral expansions from dykes 

 which cross these at angles. Both the classes of rock which 

 form these eminences dip to the east at an angle of about 

 30°, The trap rock of St Leonard's Hill is a slightly por- 

 phyritic greenstone ; but, as it approaches the sandstone 

 on which it rests, it changes its mineralogical characters 

 and passes into a red greenstone of a more compact struc- 

 ture, or into a brownish red ferruginous claystone-felspar : it 

 contains small imbedded masses of calcareous spar, and is 

 also traversed by veins of the same mineral, which are fre- 

 quently associated with radiated red haematite. Immediate- 



