DUNBAR HARBOUR. 97 



Plutonic rocks, and large portions are enveloped in them 

 and indurated to a great extent. The trap deposit on 

 which the Castle of Dunbar is built differs in different parts 

 — in some places being composed of varieties of red basaltic 

 greenstone, and in others of tufa ; and in one place, where 

 the sea has formed an arch, masses of indurated sandstone 

 of many yards extent are entangled in the trap rock. Con- 

 cerning the relations of the greenstone of the rock of Dun- 

 bar Castle to the tufa, we may state that, though in some 

 places it appears of a newer formation, still a complete exa- 

 mination allows only the conclusion to be drawn, that the 

 rocks of this point have been the result of igneous actions, 

 which were not discontinued till all these masses were ela- 

 borated.* 



Between this and Dunbar Harbour, sandstone strata oc- 

 cur arranged in the most irregular manner, dipping to va- 

 rious points, and in some places sinking under the trap of 

 the Castle ; they are here" also broken through by another 

 intrusive mass of greenstone, but their immediate modes of 

 connection cannot be made out. At the harbour tufa oc- 

 curs of the same description as that which we have already 

 noticed, and is traversed by a rock which may be described 

 as a very fine granular ferruginous felspathic greenstone, 

 which, in some places, becomes porphyritic from containing 

 minute crystals of felspar. The structure of this rock is 

 beautifully prismatic, the columnar concretions being, in 

 some instances, fifteen feet in length : they vary in the num- 

 ber of their sides; figures of three, five, and six sides are, 



* The interesting geological phenomena which the castle rock of Dun- 

 har exhibits can only be perfectly examined from a boat, and observers 

 who desire to investigate this locality in detail, will find a correct guide 

 in a map lately published by Mr J.Mason, Land-surveyor, Belhaven, 

 and entitled " Plan of Dunbar Castle and Bay Rocks.'' 

 VOL. VII. G 



