C. Johns—Classification of the Lower Carboniferous Rocks. 563 
with which they are faunally and physically linked. There should 
be no difficulty in selecting a name for this great division of the 
Carboniferous System. The work that has been done by Dr. Arthur 
Vaughan on the Avon section, and the impetus which the publication 
of his conclusions gave to the study of the Carboniferous Limestone in 
this country and abroad, at once suggests the acceptance of the term 
Avontan in preference to Bernician or Dinantian. 
For the divisions of the Avonian we have in common use the terms 
Tournaisian and Viséan. If only in fairness to the Belgian workers 
who established these divisions, and in recognition of the value of their 
contribution to our knowledge, these terms should be retained. It has 
been demonstrated ' that the line drawn in Belgium corresponds exactly 
to the physical break in South Wales at the base of the Viséan, and 
is the well-known C-S level of North-West Yorkshire and Westmore- 
land. Thus the dividing line between Tournaisian and Viséan is, and 
can only be, drawn at the same horizon in these widely separated areas. 
It is not so easy to define the upper limits of the Viséan, for the 
Avonian coral and brachiopod fauna persisted longer in some districts 
than others, but over wide areas it gave place, as a result of physiographic 
changes, to a new fauna, chiefly cephalopods and lamellibranchs, which 
persist to the summit of the Lower Carboniferous. Itisto Dr. Wheelton 
Hind we owe the demonstration that this fauna which characterizes the 
Lower Culm is the same as that of his Pendleside Series. Viséan 
cannot be made to include this Culm or Pendleside fauna, which can 
be seen in Derbyshire, Yorkshire, and Lancashire to succeed it. 
Level of the Plant break. 
Upper 
Carboni- 
ferous 
Upper} Upper Yoredale Coral Fauna. 
a Yoredalian 
2 Lower| Entrance of Lower Culm or Pendleside fauna 
& iz (Posidonomya Becheri). 
3 <— 
o =! 
ce Ae ee 
Ss S | Viséan 
i =< Entrance of C-S fauna (Caninia patula, Clisio- 
BS phyllum Ingletonense). 
So 
e Tournaisian 
The difficulty, however, has been to determine the relationship 
between the Yoredale rocks of the typical Yoredale district and the 
Pendleside Series. Reasons have been given” for correlating the 
Posidonomya Bechert beds of the Pendleside Series with the Lower 
Yoredales, and it might be further pointed out that the coral fauna of 
the Upper Yoredale limestones is an appreciable advance on the D, of 
South Wales. Perhaps even more important is the fact that at the 
1 Arthur Vaughan, Brit. Assoc. Reports, Carboniferous Fauna, 1910. 
2 Hvidence for this will be given in the Naturalist, January, 1911, p. 9. 
