28 GEOLOGY OF THE EAST LOTHIAN COAST. 



strata are bent down so as to dip into the neck all round its 

 margin." We are not aware to what other instances Prof. Geikie 



o 



may allude; but on referring to his Memoir on the Geology of 

 East Lothian, we find that he states in the cases of 'North 

 Berwick Law' and 'Traprain' (which he compares with the 

 igneous mass at Whitberry Point), that the beds at the base of 

 these two necks, where exposed, dip away from them, and that 

 at a high angle. 



In support of the hypothesis which we have put forward, the 

 following arguments may be urged : 



(1) That in one place at least the sedimentary strata are 

 seen to be actually dipping beneath the superincumbent basalt; 

 and that the impression produced by the general relation of the 

 two rocks is, that they do so everywhere. 



(2) Since the columns into which the lava is split are verti- 

 cal, the cooling surface must have been horizontal : the mass 

 must, therefore, have formed a sheet, and not a dyke ; for, in the 

 latter case, the cooling surfaces would have been vertical. 



(3) It is difficult to conceive, on the supposition that the 

 volcanic rock is a neck with perpendicular sides, that the marine 

 denudation should have uniformly proceeded only so far as to 

 lay bare the junction between the two formations. We should 

 have expected that in many places the igneous rock itself would 

 have been cut down to the general level, whereas the only signs 

 of such an effect are shown in a few narrow inlets where the 

 rock was manifestly softer than in the surrounding parts. 



The last objection is greatly confirmed by the overhanging 

 cliffs and numerous blocks of porphyrite which lie scattered on 

 the beach, as if to attest the former extension of that ancient 

 sheet of which these blocks now form but a small remnant. In- 

 deed, the existence of such remains appears sufficient of itself to 

 condemn any hypothesis which presumes the present face of the 

 cliff to have formed the original boundary of the mass. 



It may be fairly objected to our theory, as Prof. Geikie him- 

 self has suggested, that the high angle at which the strata dip is 

 difficult to account for. But, in fact, this steep inclination con- 

 stitutes the very difficulty which any hypothesis on the subject 

 must be framed to explain; and it is a difficulty which is not 

 more easily solved by Prof. Geikie's theory than by our own. 



