1911-1912.] An Account of the Exctcj'sions {igi2), 453 



situated on the shore close to GuUane Point. These rocks 

 consist for the most part of dolerite which has lost much of 

 its characteristic appearance by being intruded among car- 

 bonaceous shales, being converted thereby into a species of 

 igneous rock known as " white trap." To the east of the 

 Hummell Kocks, and just above high-water mark, stands the 

 prominent ridge called Corby Craigs, composed of ordinary 

 dark-coloured dolerite. One object of the excursion was to 

 point out that this ridge is directly connected with the " white 

 trap " of the Hummell Kocks, and is not a separate intrusion, 

 as before supposed. The fact was proved by conclusive 

 evidence easily seen on the ground. 



The really peculiar feature connected with the Hummell 

 Eocks is the large number of narrow vertical dykes (Plate 

 XL., Fig. 1) by which they are intersected. On carefully 

 studying these dykes, and also a large fissure which nearly 

 cuts the Hummell Eocks in two, they are found to consist of 

 sedimentary material altered by heat and containing frag- 

 ments of the white trap. These dykes appear to be of the 

 nature of veins which have been squeezed up from below, at 

 a time when the great mass of the intrusion was on the point 

 of solidification into joints and cracks, probably caused by 

 some movement of the mass at the same time. This veining 

 of an intrusive mass with sedimentary material is peculiar, 

 and has not apparently been previously observed in this 

 country. That these dykes do not represent the infilling of 

 cracks on the upper surface of an old lava flow is abundantly 

 proved by the evidence to be seen on all sides of the intrusive 

 nature of the sill. The attendance at this meeting was 

 very large, numbering upwards of seventy, but this included 

 several members of the Geological Society and of the Scottish 

 Natural History Society, who joined the excursion at 

 Gullane. 



The next excursion was also conducted by Mr T. C. Day, 

 and thirty-seven members went to Bilston Burn (Plate XL., 

 Pig. 2) to view the Lower Limestone of this locality, where 

 there is one of the best sections of the Lower Limestone 

 series to be seen in the district. The strike of the rocks is 

 nearly from N.E. to S.W., and they dip at an angle approach- 

 ing 50° towards the S.E. This wall of successive strata, some 



