266 
HUGHES : ADAM SEDGWICK. 
In 1 843 he filled in some details but made no change in the 
order of succession. The following- series shows what he included 
in his Bala beds. 
a. Slates W. of Areing, with a large trilobite, like Asaphus (Ogygia) 
Buchii ? 0. peltata. 
b. Slates with interbedded volcanic ejectamenta. 
c. Dark earthy slates, with Trinucleus Caractai (= T concentricus), 
Asaphus Powisii, Leptaena sericea, encrinites, &c. 
d'd". Shales with subordinate Limestone, d', from which he gives very full 
hsts of fossils. 
Then follow other shales, d'", and above them the Hirnant 
Limestone, e, the true relations of which I hope to describe 
elsewhere. 
Many of Sedgwick's old sections, which he exhibited when 
these papers were read are still in existence, and represent what is 
found recorded in the published papers. They can be compared 
with the Survey sections. It will be seen that the Survey has 
drawn no lines not pointed out b}'' Sedgwick, and when it has indi- 
cated by letter the occurrence of formations not mapped, it will be 
seen that Sedgwick had suggested their separate existence long 
before. 
Take the section from Trawsfynydd to Cynicht. It was made 
in 1846 from Sedgwick's much earlier notes. His papers of 1838 
give the sequence, and from a comparison of this with the Survey 
section (28, C and D), it will be seen that they adopted all his 
classifications. This section is taken across the typical district from 
which later he named the whole of the Lingula flags, the 
Ffestiniog group. 
In other sections described in his papers, he gives the Lingula 
beds, the Pisolitic iron-ore beds, i.e. Arenig and the overlying slates, 
all of which are mentioned in the text under the head of Cambrian. 
The section from Pentrevoclas to Abergele shows the grits 
which Sedgwick took as the base of the Silurian, below which he 
supposed the unconformity to occur, which he mentioned in his 
paper before the Geological Society, above quoted. 
The Survey did not set aside but confirmed Sedgwick's classi- 
fication over all N. Wales. Where was the difiiculty? Why, in 
