284 Correspondence. 
all serving to confirm the identity. ‘There is a slight lithological 
difference, however; one portion, marked d, differing from beds in the 
like position in the main band, in the paleness of their colour and 
the admixture of a considerable quantity of sand; for which reason, 
by the way, this limestone is not so highly esteemed for agriculturai 
purposes as the former. The beds are perched up at very great 
angles; the lower beds are not worked; but, by measuring the 
out-crop of the strata, it is evident that we have the whole series of 
beds as developed in the main band, corresponding in general order 
and character, though differing in one or two minor lithological 
features. 
The question arises, does this outlier owe its isolated position to 
the denudation of beds by which it was once connected with the 
main band, or to the operation of the same causes which led to the 
deposition of the latter, working in a limited area ?—in other words, 
was it once connected with the main band, or was it originally depo- 
sited apart from the rest? ‘Uhe theory of denudation is now in 
considerable favour; and I find that, in a former number of this 
Magazine, Mr. Jukes expresses his belief that this very outlier 
formed part of the ‘ whole Carboniferous series, which at one time 
covered a great part of Wales; the remaining portions, and those 
once connecting it with the main band, having been washed away. 
It may savour of presumption to differ from so great an authority ; 
and yet, knowing the country as I do, I am compelled to dissent 
from such a notion. Let us look a little more closely into the 
matter. The Carboniferous Limestone of the North Wales border is 
between 300 and 400 feet in thickness, the bulk of it consisting of 
limestone proper. The outlier near Corwen is distant about eight 
miles from the nearest point of the main band. Without assuming, as 
Mr. Jukes would, that the whole Carboniferous series once covered 
nearly the whole of North Wales, let us suppose that the main lime- 
stone once extended along its whole course of forty miles, eight 
miles only beyond its present outcrop, we have then a deposit of 
limestone (to say nothing of the other members of the Carboniferous 
group), 850 feet or thereabouts in thickness, covering an area of 
320 square miles. Now it is quite evident that, if this mass of cal- 
careous matter has been swept away, it has been redeposited some- 
where else, in the newer formations. If it has been denuded, have 
we any indications of the course it took—of the locality where most 
of it at least would be deposited? Is there in any of the newer 
formations any deposit analogous to it? Let us see. The pebbles 
in the Millstone-grit, those in the sandstones of the Coal-measures, 
those in the Permian and Trias, and notably the matcrials of the 
‘Drift’ on the Welsh border, and in the plains of Salop and Chester, 
all indicate currents running eastward. With reference, then, to 
the particular district under notice, in this direction we should look 
for this denuded and redeposited matter. And in the extensive 
plains of Shropshire and Cheshire, which lie between the eastern 
development of the Carboniferous strata in Derbyshire, Stafford, and 
South Shropshire, we ought, if anywhere, to find these denuded mate- 
