58 GEOLOGY OF THE LOTHIANS. 



the sandstones and greenstones of Salisbury Crags. (Plate 

 VII. Fig. 2.) Imbedded in the tufa on the east side of the 

 principal basaltic vein, a mass of white sandstone occurs ; 

 it is not, however, much altered in structure. Forming the 

 highest point of that part of the hill which rises above the 

 village of Duddingston, another basalt is to be observed ; it is 

 arranged in perfect columns, which vary in the number of 

 their sides. The composition of this basalt differs from 

 that which forms the summit, in being less compact, and 

 containing large crystals of Labradorite Felspar, Basaltic 

 Hornblende, and numerous disseminated masses of Olivine. 

 Imbedded in the trap which forms the southern acclivity, 

 there occur several masses of calcareous sandstone of many 

 yards extent ; they are completely changed in character, 

 some portions becoming a conchoidal horn stone, while others 

 pass into chalcedonic quartz. 



At the northern extremity of Duddingston Loch, there 

 is a mass of greenstone, identical in mineralogical cha- 

 racters with that of Salisbury Crags, and upon it reposes 

 a series of sandstone and slate strata, presenting all the cha- 

 racters of induration. On examining the points of contact 

 of these rocks, masses of the sandstone may be found par- 

 tially enveloped in the greenstone, and compressed into the 

 form of a vein ; similar appearances are also to be observed 

 in Salisbury Crags. On the side of the road which runs 

 through the ravine of Windy Gowl, fragments of moun- 

 tain limestone crop out, but their relations to the Plutonic 

 rock cannot be made out. Concerning the relations of the 

 trap of Arthur's Seat to the sandstone of Duddingston, it 

 may be mentioned, that the want of sections prevents us 

 from acquiring information in regard to its intimate connec- 

 tions with the igneous rocks ; as, however, at Niddry Mill, 

 a distance of two miles, the coal strata are found inclining 



