ANNIYERSART ADDRESS OF THE PRESIDENT. II3 



(e) Rochs of the Necks. — In many of the necks connected with the 

 Plateaux other types of massive rock are to be found. Among 

 these, perhaps the most frequent are felsites, yellow, grey, and 

 pink in colour, exceedingly compact, sparingly porphyritic, and 

 showing small blebs or large porphyritic, more or less rounded, 

 crystals of quartz. Acid rocks of this character also appear as sills 

 and dykes. Other varieties that occur in similar positions are more 

 basic in composition, including dark, coarse, granular diabases. In 

 the Jedburgh district the most frequent rocks are beautiful varieties 

 of olivine-basalt, which form most of the prominent hills of the 

 neighbourhood. Not a few of these masses occur as necks, some- 

 times with agglomerates. 



In the Garlton Hills district some of the necks present another 

 petrographical type which directly connects them with the remark- 

 able lavas of the higher part of that plateau. Thus the rock of 

 Traprain Law is of a trachytic character, and in the opinion of 

 Dr. Hatch proves to be really a phonolite. He is now engaged 

 in its investigation. In its general platy structure and sonorous 

 ring under the hammer it reminds one of some true phonolites. 

 The neck of North Berwick Law the same observer finds to be 

 also a trachyte, showing a plexus of lath-shaped sanidines that 

 diminish in size to minute microlites, but with no porphyritic or 

 ferro-magnesian constituent. The Bass Eock, though its geolo- 

 gical relations are concealed by the sea, is in all probability another 

 neck of this district. It proves to be likewise a mass of trachyte 

 composed almost entirely of lath-shaped crystals of sanidine with 

 no ferro-magnesian constituent, but a good deal of iron ore. It 

 shows none of the large porphyritic felspars so characteristic of 

 the Garlton Hills lavas, but it closely resembles some of those rocks, 

 particularly the lavas of Score Hill, Pencraig, Lock Pit Hill, and 

 Craigie Hill. The occurrence of trachytic rocks in the bosses 

 around the Garlton Hills marks them off from the usual diabases 

 and basalts of the basin of the Firth of Forth, and directly connects 

 them with the trachyte-lavas of the district, while the presence of 

 phonolite among them is of special interest. 



The rock of Traprain Law was analysed for me in Dr. Frankland's 

 laboratory, with the results given in the table on the following 

 page. This analysis shows a close agreement with the compo- 

 sition of the Bangley rock as stated in the previous table. Un- 

 fortunately the alkalies were not separately determined. 



