O. W, and F. M. Balfour — On the East Lothian Coast. 163 



the sheet of lava after it has overspread the surface of the sandstone 

 beds B., so as to cause them to assume their present inclination. The 

 dotted lines represent the hypothetical extension of the igneous mass 

 and sandstones previous to the denudation which they have suffered 

 from the action of the waves. 



Professor Geikie, in his admirable treatise on the Geology of the 

 county,' adopts a view on this subject which is somewhat different 

 from that which is suggested in this paper. He considers that the 

 whole mass is an intrusive neck of rock with perpendicular sides ; 

 and that it once filled up an orifice through the surrounding sedimen- 

 tary strata, of which it is now the only remnant. 



He admits that the inclination of the sandstone beds towards the 

 igneous mass in the centre is a phenomenon that is somewhat diffi- 

 cult to explain, and suggests that a subsequent contraction of the 

 column may have tended to produce such a result. To use his own 

 words : " In the case of a solid column of felstone or basalt, the 

 contraction of the melted mass on cooling may have had some effect 

 in dragging down the sides of the orifice." ^ 



But, apart from other objections> it is scarcely conceivable that thi& 

 result should have been produced by the contraction of the column. 



In his recent edition of Jukes's Manual of Geology (p. 269), 

 in which he also^ refers to this instance, he states that in other cases- 

 of " necks " it is found to be an almost invariable rule, " that 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 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 vertical,, 

 the cooling surface must have been horizontal :. the mass must, there- 

 fore, 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. 



1 Memoii-s of Geological Survey of Scotland, Sheet 33, pp. 40, 41. 



2 Note on p. 41 of Mem. Geol. Survey of East Lothian. 



