06 GEOLOGY OF THE LOTHIANS. 



A short distance from the coast, the hill of Knockinghair 

 rises ; it is composed of a highly ferruginous compact trap, 

 and exhibits a structure which might at first be considered 

 brecciated. On examination, however, this fragmentary ap- 

 pearance will be found to be only an instance of that original 

 concretionary structure, which, in many instances, may with 

 little difficulty be confounded with a rock of a true frag- 

 mentary nature. Numerous large and well defined cry- 

 stals of basaltic hornblende are frequently to be found in 

 the trap of Knockinghair. 



Between the termination of the tufa, which forms the cliffs 

 to the west of Dunbar, and the trap on which the castle is 

 built, the shore is formed of sandstone, which dips to the 

 E. S.E. at a small angle. At this point a mass of trap, 

 which is known by the name of the Doo Rock, rises through 

 the sandstone strata ; it is in some places a basaltic or amyg- 

 daloidal greenstone, while in others it partakes of the tufa- 

 ceous character. The strata with which this rock is in con- 

 nection in some instances abutt against it, and in others sink 

 below it. In several places great masses of the sandstone 

 are enveloped in the trap, all of which are changed in their 

 mineralogical characters, becoming either conchoidal horn- 

 stone or granular quartz-rock, and frequently acquiring a 

 green colour, from an intimate commixture with the augite 

 of the trap. At a short distance from this rock the trap of 

 the Castle rises vertically through the strata of sandstone ; 

 the western part of this mass is composed of a red felspathose 

 porphyritic greenstone, and, at the junction of the sandstone 

 with the trap, and for the distance of several yards, the 

 strata become intensely indurated, almost passing into jasper, 

 and losing, to a considerable extent, the distinctness of the 

 lines of stratification so apparent in other places. After rising 

 through the sandstone the trap flows over it, and joins an- 

 other mass of trap ; the strata are slightly bent up by these 



