I. ON SOME POINTS IN THE GEOLOGY OF THE EAST 



LOTHIAN COAST \ 



By G. W. and F. M. BALFOUR, Trinity College, Cambridge. 



THE interesting relation between the Porphyrite of Whit- 

 berry Point, at the mouth of the Tyne, near Dunbar, and the 

 adjacent sedimentary rocks, was first noticed, we believe, by 

 Professor Geikie, who speaks of it in the Memoirs of the Geologi- 

 cal Survey of East LotJiian, pages 40 and 31, and again in the 

 new edition of Jukes's Geology, p. 269. The volcanic mass 

 which forms the point consists of a dark felspathic base with 

 numerous crystals of augite: it is circular in form, and is exposed 

 for two-thirds of its circumference in a vertical precipice facing 

 the sea, about twenty feet in height. 



The rock is traversed by numerous joints running both in a 

 horizontal and in a vertical direction. The latter are by far the 

 most conspicuous, and give the face of the cliff, when seen from 

 a distance, a well-marked columnar appearance, though the 

 columns themselves are not very distinct or regular. They are 

 quadrangular in form, and are evidently produced by the inter- 

 section at right-angles of the two series of vertical joints. 



It is clear that the face of the precipice has been gradually 

 receding in proportion as it yielded to the action of the waves ; 

 and that at a former period the volcanic rock extended con- 

 siderably further than at present over the beds which are seen 

 to dip beneath it. These latter consist of hard fine-grained 

 calcareous sandstones belonging to the Lower Carboniferous 

 formation. Their colour varies from red to white, and their 

 prevailing dip is in a N.W. direction, with an average inclination 

 of 12 20. If the volcanic mass is a true intrusive rock, we 

 should naturally expect the strata which surround it to dip away 

 in all directions, the amount of their inclination diminishing in 



1 From the Geological Magazine, Vol. IX. No. 4. April, 1872. 



