Geological Society. 321 



Dr. Darwin's view of the formation of the coral-atolls and barrier- 

 reefs during depression (p. 131 &c). The author's search for a 

 true cause of the Parallel Roads has thus led him, in his somewhat 

 discursive chapters, to a world-wide view of marine conditions 

 and movements and their apparent periodicity. He has chosen 

 to the best of his judgment, and certainly in good faith, very much 

 that supports his views, both as to the direct cause of the long 

 terraces under notice, and the wide-spread conditions that may 

 have been more distantly concerned in its operation. Both to 

 those specially interested in these terraces of the Highland Grlens, 

 and to those w T ho like to study cosmical changes and great 

 terrestrial modifications, this book offers many good suggestions 

 and much to think over. 



XXXVII. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from p. 73.] 



December 19, 1883.— J. W. Hulke, Esq., F.R.S., President, 

 in the Chair. 



HPHE following communications were read : — 



-*- 1. " On some Remains of Possil Pishes from the Yoredale 



Series at Leyburn in Wensleydale." By James W. Davis, Esq., 



P.G.S. 



2. " Penological Xotes on some North-of-England Dykes." By 

 J. J". H. Teall, Esq., M.A., P.G.S. 



The author described the stratigraphical relations and the struc- 

 ture, macroscopic and microscopic, of a number of dykes which 

 occur in the north-east of England, giving analyses. He pointed 

 out that they fell into four more or less distinct groups : — 



(1) The Cleveland dyke and that of Acklington. 



(2) The Heth and its related dykes. 



(3) The dykes of Hebburn, of Tynemouth, of Brunton, of 



Hartley, and of Morpeth. 



(4) The High Green dykes. 



Groups (1) and (3) resembled one another in specific gravity and 

 chemical composition, as did (2) and (4), the percentage of silica 

 in the first two (except in the Morpeth dyke) varying from 57 to 59, 

 and the specific gravity being about 2*7 or 2*8, while the others had 

 a silica percentage of from 51 to 53 and a rather higher specific 

 gravity. The former present some microscopic differences, the latter 

 are very closely related. The Cleveland, Acklington, and Heth 

 dykes have been examined at intervals far apart, and exhibit no 



