Rev. A. Irving — On the “ Permian ” and “ New Redl 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 saudstones 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 great 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 liope 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 bis ‘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 ; (5) 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 Rocks,” 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 
