148 THE STRUCTURE AND AGE OF ARTIITTR's SEAT, EDINBURGH. 



of a later date for the cone of Arthur's Seat, that he did not see 

 there was any a priori difficulty in supposing a second volcanic out- 

 burst in one district after a long lapse of time, and that the volcanic 

 district of West Scotland (so well described by Mr. Judd), and the 

 Cleveland dyke in Yorkshire showed that there had been volcanic 

 disturbances over a large area after Palaeozoic times; so that he 

 thought there was something still to be said for the old theory. 



Mr. Judd, in reply, stated that the junction of the Highland rocks 

 with the strata lying to the southward was usually very obscure : 

 nevertheless Prof. Nicol had shown that where a clear section was 

 exposed on the coast, the newer Palaeozoic rocks were clearly faulted 

 against the older Palaeozoic, in the same manner as on the south 

 side of the Central Valley of Scotland. This question was, however, 

 one quite incidental to the line of argument of the paper. Although 

 intrusive sheets of rock usually follow the planes of stratification of 

 the rocks among which they are injected, yet many examples occur 

 of their cutting obliquely across the strata for short distances. He 

 had not attempted to describe all the interesting phenomena of 

 Arthur's Seat, but had devoted his remarks to that part of the 

 subject concerning which the accepted theory did not appear to be 

 satisfactory. He did not deny the possibility of later eruptions 

 taking place on the same site as those of a former period, but 

 maintained that the onus of proving that such was the case in the 

 present instance lay with those who rejected the more simple 

 theory. 



