﻿Rev. A. Irving — On the " Fermian " and " New Red'' 311 



existed somewhere to the Magnesian Limestone Sea, is beyond all 

 doubt ; and we believe that it was not far from the latitude of the 

 town of Nottingham ; for I suppose no one will contend that the 

 Permian series of this district has anything in common with, or 

 was once continuous with, the so-called Permian sandstones and 

 marls of Warwickshire and the adjacent counties (which, by the 

 way, I am glad to learn that Mr. Aveline is willing to relegate to 

 the Coal-measures, and so confirm the belief to which a visit of two 

 or three weeks of last winter to that county, led me). 



It is with gi-eat diffidence now, as it was four years ago, that I 

 venture to discuss with him a question for which he has so 

 much more aptitude, both from extensive observation and from pro- 

 fessional training, than one can possibly pretend to, who has worked 

 at Geology more from a conviction of its educational value than 

 from any other motive ; but I hope he will pardon my saying that 

 in geological questions we must look for the same logical coherency 

 in the evidence as we demand in other departments of science or in 

 a court of law, and that the lack of this cannot be compensated for 

 by our belief (however strong that may be), in the extensive know- 

 ledge of the observer. That the Bunter strata overlap the Magnesian 

 Limestone in Nottinghamshire is evident enough, but I could not 

 see (nor can I see yet) that this necessarily implies unconformity 

 resulting from the disturbance and general denudation of the imme- 

 diately subjacent strata. This may or may not accompany the 

 phenomenon of " overlap " ; and whether it actually does or not 

 must be decided, in a case like the present, by examination of actual 

 sections ; but here we find, as section after section is added to the 

 list of those previously exposed, that the great break (as evidenced 

 by observed unconformity) is below the " Permians," and not above 

 them. I do not for a moment maintain that there is " perfect con- 

 formity " everywhere between the Permians and the Bunter ; but I 

 believe that such slight unconformities as are actually observable at 

 this particular horizon are not a whit greater, and have no more 

 general significance whatever, than such as (according to my own 

 observation, and Mr. Aveline's showing in his 'Memoir') exist 

 between different members of the Permian and Trias themselves ; 

 and especially (a) between the Magnesian Limestone and the 

 stratified red and purple Permian marls that lie upon its eroded 

 surface at Mansfield and elsewhere; (h) at the junction of the 

 Lower Mottled Sandstone and the base of the Bunter Conglomerates, 

 as seen in section in the " Hemlock Stone" ; (c) at the junction of 

 the Bunter and the Keuper, several sections of which in the neigh- 

 bourhood of Nottingham I have previously described. For further 

 information concerning such minor and localized unconformities, I 

 may refer to Mr, Aveline's memoir on " Parts of Nottinghamshire 

 and Derbyshire," p. 11, and to Prof. Hull's memoir on the 

 "Permian and Triassic Eocks," figs. 11, 12, 13, 14, and 16. 



It is no reflexion upon Mr. Aveline personally, nor in any sense a 

 depreciation of the officers of H.M. Geological Survey or their most 

 valuable work, to suggest that generalizations may have been, in 



