THES LOWER» SILURIAN: PERIOD. 93 
3. The Caradoc or Bala Group.—The alternative names of 
this group are also of local origin, and are derived, the one 
from Caer Caradoc in Shropshire, the other from Bala in Wales, 
strata of this age occurring in both localities. The series is 
divided into a lower and upper group, the latter chiefly com- 
posed of shales and flags, and the former of sandstones and 
shales, together with the important and interesting calcareous 
band known as the “ Bala Limestone.” ‘The thickness of the 
entire series varies from 4000 to as much as 12,000 feet, ac- 
cording: as it contains more or less of interstratified igneous 
rocks. 
4. The Llandovery Group (Lower Llandovery of Murchison). 
—This series, as developed near the town of Llandovery, in 
Caermarthenshire, consists of less than tooo feet of conglom- 
erates, sandstones, and shales. It is probable, however, that 
the little calcareous band known as the “ Hirnant Limestone,” 
together with certain pale-coloured slates which lie above the 
Bala Limestone, though usually referred to the Caradoc series, 
should in reality be regarded as belonging to the Llandovery 
group. 
The general succession of the Lower Silurian strata of Wales 
and its borders, attaining a maximum thickness (along with 
contemporaneous igneous matter) of nearly 30,000 feet, is 
diagramatically represented in the annexed sketch-section 
(fig. 34) :— 
[GENERALISED SECTION 
