88 Proceedings of the Royal Physical Society. 



and shales, it may frequently be observed cutting across the 

 sedimentary rocks, and sending veins of pink felsite across 

 the lines of bedding of the quartzites. We are inclined to 

 believe that the nietamorphisni which the Old Eed Sandstone 

 rocks have undergone between Weesdale and Sandness may 

 be due to the existence of masses of granite not far from the 

 surface, for it is highly probable that the isolated masses of 

 highly siliceous intrusive rocks in the west and north of the 

 Mainland are connected underneath, though this cannot be 

 proved to be the case on the surface. 



On both sides of Noss Sound, in Bressay and Noss, we dis- 

 covered a series of volcanic pipes filled with a coarse 

 agglomerate made up of fragments of the stratified rocks 

 pierced by these vents. There is a singular absence of blocks 

 of porphyrite in the agglomerate, but a thin vein of this rock 

 is traceable for a short distance along the side of the old 

 orifice. 



Farther on the shores of Eoeness Voe, as well as in Meikle 

 Eooe, the quartz-felsites are traversed by a series of porphy- 

 rite dykes running in a north and south direction, which 

 probably represent the last indications of volcanic activity 

 during the Old Eed Sandstone period in Shetland. 



X. On the Classification and Affinities of the " Tahidate 

 Corals!' By H. Alleyne Nicholson, M.D., D.Sc, 

 F.E.S.E., Professor of Natural History in the Univer- 

 sity of St Andrews. 



{Read 29th May 1879.) 



In the present communication I purpose giving a very 

 brief general sketch of the structure and relationships of the 

 so-called " Tabulate Corals," a group of Ccelenterates which 

 I have been long engaged in investigating by means of 

 modern methods of research, and which I shall treat of in 

 considerable detail in a work now passing through the press. 

 In the following remarks I shall confine myself to giving 

 merely a short account of the results which have been 



