8 NOTES ON THE GEOLOGY OF 
e. Denbigh Flags. 
jf. Lowest shales of Silurian, having as the basement bed 
g. Whitish Grit, about 50 feet thick, becoming finer as we follow it to 
the west, until it is represented by striped nodular beds, the 
nodular character being due to squeezing up of lenticular beds of 
sandstone. 
hk. Bala Beds, consisting of light-coloured slate, sometimes showing 
double cleavage. 
From the beds on Bryngorlan I procured Leptena sericea, and 
transversalis, Strophomena rhomboidalis, (Dalm), Palearca and 
various indeterminable fragments. These fossils do not certainly 
fix the horizon, but the geological position of the beds, suggested 
by their lithological character, is rendered more probable by 
the determination of the base of the Silurian which overlies 
them on the south. [See Q.J.G.S., Vol. xxxiii., 1877, p. 207. | 
We hope for valuable results from the excellent work being 
done by Mr. Ruppy among these rocks a little further south in 
the Dee Valley. 
The beds passed over by the Clwyd, N. of Bettws-y-gwerfilgoch, 
belong to the same part of the Series. They are well exposed 
further S. and W., and form the uppermost part of the main mass 
of Bala in its typical district.* 
The same beds are exposed on Cyrnybrain (see fig. 3.), a 
district that requires and would probably repay careful work. 
There are some fossiliferous shales on the South Eastern slopes 
which seem to belong to the Lower May Hill Series (* of fig. 3.) 
Fic. 3. 
Section across hills S. of Vale of Clwyd. 
A! Silurian Flags and Sandstones. 
A? Dark bluish slates, extensively quarried. 
A3 Pale Slates. 
A‘ Coarse fossiliferous Grit, broken up along the outcrop. 
* .(?) Some Lower May Hill Mudstone. : 
B! Bala Beds with fossils. 
B? Bala Sandstone. 
F Faults. 
SILURIAN (SEDGW.) 
Overlying the Bala Beds we always find a series of deposits 
showing a change from the conditions which furnished the fine 
felspathic muds of the Bala Series, and yet there seems to have 
been much of the same kind of material derived either first hand 
or second hand from volcanic eruptions, still carried about in 
the currents, so that we often have pale, pasty, felspathic mud- 
stones in the base of the Silurian. There is not evidence of any 
strong break; it is not clear that the sea bottom was raised 
above the water level, or that land conditions prevailed in this 
area between the two periods, but we always have a sudden 
incoming of coarser material, a conglomerate, or a grit or 
* For some of the subdivisions of the upper beds see Marr Q.J.G.S., Vol. xxxvi., p. 207. 
