310 Rev. A. Irving — On the “ Permian ” and “ New Red." 
Ihe Geological Survey upon the district. The more the matter was 
studied, the more did I lose confidence in the dictum above referred 
to, and I could not help coming finally to the conclusion, as Prof. 
Phillips had done, with reference to the same two series of rocks 
in another area, that ‘‘ their physical history was upon the whole 
one great series of natural operations.” Nor had I overlooked, 
as Mr. Aveline 1 seems to imagine, the few and rneagre data which 
were furnished by him and by Prof. Hüll in their respective 
“ Memoirs,” from which their conclusions as to the great uncon- 
formity hetween Bunter and Permian was drawn. It is not for me 
to point out to Mr. Aveline. or to any other geologist so practised 
and experienced in field-work as he is, that we have here a question 
where we must decide, if at all, by the balanoiug of probabilities. 
The direr.t evidence of any great unconformity is very weak 
indeed. The intercalation of the middle marls and saudstones by 
Worksop and northward furniskes very little proof of the removal 
by post-Permian denudation of the Upper Magnesian Limestone as 
we proceed south ; as I tliink any one will see who will take the 
trouble to weigh well the reasoning of Mr. E. Wilson, F.G.S., in the 
May Number of this Magazine (p. 238). I must say that I agree with 
tliis gentleman entirely as to the true interpretation of the facts 
reiterated with so muck emphasis by Mr. Aveline in bis recent. 
communication to this periodical : facts which both Mr. Wilson and 
myself were fully eonversant with, since they were stated years ago 
in the “ Memoirs.” And not only are we now in a better position 
to judge of their true bearing, on account of the great accession to 
our stock of data which has beeil furnished by the recent develop- 
ment of the South Notts Coal-field ; but I venture to say that any 
one who had seen the great intercalated masses of dolomitic 
sandstone which are quarried in the neigkbourhood of Mansfield, 
miglit well feel sceptical (in the absence of palaeontological evidence) 
as to the precise identity of a particular member of the Magnesian 
Limestone grcrnp at Worksop, with the beds that occur between 
Mansfield and Nottingham; where the lateral Variation of the whole 
series is so great, and the general tendency of even the dolomite 
itself to become more and more coarse-grained, flaggy, and gritty in 
its progress soutkward, is most. pronounced. Nor do I forget (even 
with the circumscribed geological vision of a “local geologist”) that 
this is in general karmony with the tkinning-out of the whole series 
of the Magnesian Limestone from a tliickness of 600 feet in the 
couuty of Durham, to thatof a few flaggy bands in Nottinghamshire. 
Every one who has done any field-work at all, must know how 
liazardous it is to generalize in a spirit approacking to anything like 
dogmatism, on the actual relation of two sets of rocks, both of which 
are unfossiliferous, unless they had been traced continuously across 
the country ; and this Mr. Aveline, with the small amount of data 
afforded, will scarcely maintain to have been done in the present 
instance. That a Southern and soutk-western boundary must have 
1 See Mr. Aveline’s article in the April No. of Geol. Mag., p. 155, “ On the 
Magnesian Limestone and the New Ited Sandstone of Nottingham.’’ 
