268 MESSRS. STRAHAN AND WALKER ON PEBBLES 
21. On the OccurreNcr of PeBBies with Uprrr Luptow Fossirs in 
the LowrR CARBONIFEROUS ConcLomERATES of NorrH WaALEs. 
By Ausrey Strawn, Hsq.,M.A., F.G.S., H.M. Geological Survey, 
and Atrrep O. Waker, Esq., F.L.S. (Read February 5, 
1879.) 
[By permission of the Director-General of the Geological Survey of 
Great Britain. ] 
Neary forty years ago Mr. Bowman drew attention to ‘a small 
patch of Silurians west of Abergele.” in which he described the 
following subdivisions in descending order*:— _ 
J. A conglomerate of pebbles of greenish micaceous sandstone in a light 
loamy earth resting on a similar sandstone. 
e. Thick red marl with numerous pebbles of red sandstone, micaceous, with 
many bivalves. 
d. A hard compact conglomerate of green sandstone and quartzose rock. 
e. Compact red limestone. 
b. Fine blue loamy clay. 
a, Clay-slate. 
He makes the observation that the red-sandstone pebbles in 
bed ¢ resemble Ludlow rock, and names four Ludlow species as 
occurring in them. 
Our attention was directed to these beds by numerous excavations 
made in them at the time of the recent activity in the iron trade. 
The only good exposure is in Ffernant Dingle, a deep ravine running 
from the Pen-y-Cefn lane southward past Cefn-y-Fran, about one 
mile south of Llysfaen. 
The southern or lower end of this dingle is occupied by Wenlock 
shale, a pale blue slaty clay, with occasional sandy beds. The beds 
are much jointed, and sometimes cleaved so as to weather into 
pencil-like fragments. At the south end of the dingle they are 
nearly horizontal, but dip gently to the north higher up, near Cefn- 
y-F ran. 
: At this point the Wenlock shale is unconformably overlain by 
hard, mottled, red and green brecciated limestone, containing beds 
of green sandstone pebbles in a sandy matrix. ‘The limestone and 
the conglomerates dip to the N.N.E. at 28°. 
This limestone constitutes bed c of Mr. Bowman’s section. It ig 
exceedingly hard, with a hackly fracture, of a green colour mottled 
with red. It contains perfectly angular fragments of Wenlock shale, 
and rounded pebbles of a greenish sandstone; there is also so large 
a proportion of quartzose and argillaceous impurity in it as to give 
* Geological Transactions, vol. vi. part 1. 
