Q4. HISTORICAL PALAEONTOLOGY. 
GENERALISED SECTION OF THE LOWER SILURIAN ROCKS 
OF WALES. 
Fig. 34. 
May Hill Sandstone (base 
of Upper Silurian). 
VERY 
GROUP. 
Llandovery Group. 
LLANDO- 
Upper Bala. 
Lower Bala. 
CARADOC OR BALA GROUP. 
eB Upper Llandeilo. 
S 
oO 
= Middle Llandeilo. 
fz) 
a 
Z 
5 Lower Llandeilo. 
ao | 
. Upper Arenig. 
= ===! 
2 aS=SS=SSSSSSSSS__===S== 
Cpl a Sema MR ee 
0 (PEATE J Ved ef pe 
Ry 7 eT 
4 Lower Arenig (Upper 
——— ne Tremadoc Group). 
SSSSS———__—__==========——=aa—S]]S== 
SaSSSSS__=_=_=======Sa== Tremadoc Slates (Lower 
—aSSSSSSSa==—]]—S" Tremadoc Group). 
In North America, both in the United States and in Can- 
ada, the Silurian rocks are very largely developed, and may be 
