TKANSACTIONS OF SECTION C. 663 



and zones were given, and it was shown how naturally the physical and palreonto- 

 logical sequence agrees with that of the corresponding Ordovician rocks of Britain 

 and Europe. The peculiar physical conditions of the Shropsliire area in Ordovician 

 times, as indicated by the very different lithological characters of the strata upon 

 the opposite sides of the Longmynd, was pointed out; the evidences for the geo- 

 logical horizons and relationships of the volcanic rocks indicated in outline, and the 

 known facts respecting the folding and faulting, and pre-Silurian erosion of the 

 Ordovician rocks briefly referred to. In conclusion, it was pointed out that the 

 clearness and simplicity of the sequence, and the highly fossiliferous nature of its 

 strata, render it tolerably certain that this Shropshire succession will form the 

 general standard to which all other British Ordovician strata must ultimately be 

 referred, 



4. On the Silurian Eocls of North Wales. 

 By Professor T. M'Kexnt Hughes, M.A., F.G.S. 



The author begins by describing some sections in the Silurian rocks of North 

 Wales. Some of them are in the lower part, some in higher beds. He gives lists 

 of fossils from the various horizons in each. He then, by means of these and by 

 what he calls syntelism, that is, the occurrence of similar sequences of beds of 

 the same characters, lithological or other, points out the corresponding parts of the 

 various sections described. 



He then does the same for the Silurian of the eastern borders of the Lake 

 district, and, having in this manner constructed a vertical section of each, compares 

 the two districts and shows that there is an identical series in each, with all the 

 important zones of one represented in the other, except that in the part of North 

 Wales which he has worked out he has not yet detected beds as high as the 

 newer part of the series in the Lake district. 



5. Notes on some Sections in the Arenig Series of Nortli Wales and the Lal-e 

 District. By Professor T. M'Kennt HriGHES, M.A., F.G.S. 



In this paper the author describes a number of sections across the Arenio- 

 series in different parts of England and Wales, and endeavours to explain some 

 apparent discrepancies in what is generally a remarkably constant set of beds. 



lie starts with the Portmadoc section, where he considers that the chief differ- 

 ences of opinion have arisen from mistakes in the explanation of the geological 

 structure of the district, especially from the wrong identification of some grit bands 

 on opposite sides of important faults. 



Following the series to the north he shows that, although they vary in thick- 

 ness, the pruicipal zones are still represented near Carnarvon ; and, discussing the 

 question of the unconformity of these beds on the Lower Cambrian, he points out 

 that the Lower Cambrian rocks are seen to vary so much both in character and 

 thickness within short distances in the neighbourhood of the existing outcrop of the 

 Archrean that any argument founded upon their thinning-out or their different 

 texture must be received with distrust in an area where thej are known to have 

 been deposited on the flanks of mountain ranges of Pre-Cambrian age. 



He then describes some localities in the Lake district where the occurrence of 

 the same zones has been determined, and explains by overlap, rather than un- 

 conformity, the difficulties, palreontological and stratigraphical, which have arisen 

 in the interpretation of those areas. 



6. On the Lower Palaeozoic Eocls near Settle.^ 

 By J. E. Mark, M.A., F.O.S. 



The sections have been described by Prof. Hughes (' Geol. Mag.' vol. iv.) and by 

 myself ('Proc. York Geol. and Poly. Soc. N. S.' vol. vii.) 



' Printed in full in the Geol. Mag. Dec. 3, vol. iv. p. 35, 1887. 



