Correspondence—Mr. Rowland Gascoigne. 187 
often more clear and trenchant—so much so that those fathers of 
British geology who made a separation between the Palwozoic and 
Mesozoic groups exercised a wise discretion in making the division 
at the junction of the two formations. This physical break is 
represented by the remarkable change in the fauna and flora of the 
formations on either side of the boundary, a fact which I fear neither 
of your correspondents has sufficiently considered. 
Epwarp HUvtt. 
THE AGE OF THE PENNINE CHAIN. 
Srr,—Having given some attention during the past few years to the 
Permian Formation in the North-east of England, I should feel obliged 
if you would allow me to say a word or two on the above subject. I 
can corroborate all that Mr. E. Wilson has said with respect to the 
physical break which exists on the north-east side of Pennine Chain 
between the Permian and Carboniferous formations; for at some of the 
new collieries which have recently been put down through the Per- 
mians in the Nottingham and Derbyshire OCoal-field, the difference 
in dip nearly amounted to twenty degrees, whilst in every case the 
unconformability between the two formations was most marked. 
The westerly attenuation of not only the Marl Slates but of the 
Permian Formation as a whole, and the sedimentary materials with 
which on the west it is intermingled, point to the existence of high 
ground in that direction during Permian times; whilst the great dif- 
ferences which undoubtedly exist in the character and thickness of 
the same formation on both sides of the existing anticlinal are facts 
altogether in favour of its existence at the time these deposits were 
laid down. I remember the surprise quite well which Professor Hull 
expressed when the Scarle boring proved the Permians to attain such 
a vast thickness in that locality, and the difficulty he experienced in 
recognizing the Marl Slates (about 150 feet in thickness), which he 
afterwards placed in the Carboniferous system. 
Under these circumstances, I fail to see how Professor Hull and Mr. 
Teall can object to the existence of the Pennine Chain during the 
deposition of the Permian formation, when such reliable facts in sup- 
port of such an existence can be produced. 
2s | 
Mexzoroven, near RorHERHAM. Row1anpd Gascorene, F.G.S. 
CRETACEOUS GASTEROPODA. 
Srr,—Mr. Wm. Gault, of Belfast, now engaged in compiling a list 
of the Irish Cretaceous fossils, has kindly forwarded to me for examina- 
tion those which appeared to be Limpets and Dentalia. The 
result has proved that the Irish species, hitherto known as Dentalium 
septangulare of Fleming, is really an Annelid. Mr. Etheridge and Prof. 
Morris agree with me in this opinion, but it is especially to Dr. Gwyn 
Jeffreys that I am indebted for a most critical examination. He states 
regarding them—‘‘ They differ from the Solenoconchia and agree with 
the Testaceous Annelida in the following particulars. They are much 
more solid and more curved, and the mouth or aperture is decidedly 
constricted. The microscopic structure showing the lines of periodical 
