14 NOTES ON THE GEOLOGY OF 
washed into hollows as the Carboniferous sea encroached on 
the land. It is not a distinct formation in any way, but only 
an irregular and local basement bed. 
Fic. 5. 
Section across base of Carboniferous Rocks in the N.W. corner of 
the Vale of Clwyd. 
a. Mountain Limestone with * caves. 
&. Basement Bed of Carboniferous, consisting of yellow and red 
sandstones and conglomerate of very variable thickness. 
c. Denbigh Flags. 
It is seen as a coarse conglomerate South of Llysfaen (see 
fig. 5), where it was noticed by Bowman in 1845, (Trans. 
Geol. Soc., Vol. vi., p. 195,) and its further extension to the 
South was pointed out to us by Mr. Price when we made an 
excursion into that district. -Its character has since been fully 
described in a paper by Mr. A. O. WALKER and MR. STRAHAN. 
(Q.J.G.S., Vol. xxxv., p. 268.) From this point it may be seen 
at intervals cropping out from below the Mountain Limestone 
to near Dinorben, S.S.E. of Abergele. There is then an 
interval of about 3 miles, and it is again picked up near Pont- 
yrddol, on the Elwy, and traced by the colour of the soil 
and an occasional outcrop for a considerable distance to 
the S.E. I have not been able to verify it as so uniform and 
continuous as indicated upon the Survey Map. In the bed of 
a small tributary of the Elwy, near Brisgill, between Pontyrddol 
and Pontnewydd, it is exposed for a short distance, and is seen 
to consist of yellowish and grey sandstones with subordinate 
bands of shale. It is a distinctly Carboniferous-looking rock, 
and contains fragmentary plant remains. I do not know that 
there is any indication of it on the East of the Vale of Clwyd; 
_ whether this is because it has been thrown down out of sight 
by faults, or because it is covered by drift, or because that area 
was further away from the sediment-supplying mountains. It 
may be seen along the valley of the Clywedog in several 
places. Between Buarthau and Felin Meredith the top beds 
of the Basement Series are exposed below the Mountain Lime- 
stone, which is faulted against a lower portion of it (fig. 6.) 
There is a passage, though a somewhat abrupt one, down from 
one formation to the other. A little further on, the base of 
the Devonian is seen resting upon the upturned and jagged 
edges of the Silurian (fig. 7), while still further south, in the 
stream below a cottage South West of Llanfwrog, near Ruthin, 
the same basement series is exposed, but here it lies upon less 
highly inclined Silurian Flags (fig. 8.) 
Ina tributary of the Clywedog, near Pandy, about a mile South 
of Llanrhaiadr, the Mountain Limestone is brought in contact 
with micaceous Silurian Flags, by a fault probably running 
along the bottom of the gorge, but it soon seems to leave the 
