Doubtful Age 
Lingula Flags 
? Menevian . 
TRANSACTIONS OF SECTION C. 
{ Castell Coch Beds—cleaved blue-black mudstones. 
Ynys Castell Beds—siliceous mudstones and cherts. 
| Ynys Castell grit and breccia, 
? break. 
Flags and laminated quartzites with Lingulella davisii. 
Slates near Abercastle with Agnostus sp. 
The ‘ Middle Llandeilo’ of Hicks’ classification has been found to include 
the Lower Dicranograptus Shales and the succeeding limestone; that is, actually 
more than the Llandeilo formation as now defined. The ‘ Upper Llandeilo’ 
includes various Lower Llanvirn and Arenig beds; the affinities of the other 
rock-groups are briefly discussed in the paper. Lingula flags occupy much of 
the adjoining inland district. 
References were made to certain ‘intrusive rocks and their relation to the 
adjoining sediments.’ The detailed mapping of the area is now in progress. 
Part II. Pwll Strodyr to Pencaer (O. T. J.). 
The following rock-groups are represented in probable descending order :— 
Lower or Middle 
Arenig 
? Lower Arenig 
Pwll Deri Slates 
Aberbach Quartzite group, 
probably equivalent to the 
Cleaved dark slates with ex- 
tensiform graptolites. 
Quartzites with thin dark 
shales. 
quartzites of Trwyn Llwyd 
and possibly of Pwll Strodyr 
Mynydd Morfa group 
Pwll Crochan group 
Lingula Flags 
Doubtful Age Dark slates with obscure 
fossils, probably Menevian. 
or Upper Lingula Flags. 
Quartzites, green and purple 
sandstones ; obscure fossils, 
? Solva Llech Dafad group 
The age and relationships of the various groups were briefly discussed, and 
reference was made to certain intrusive rocks which occur among the lower 
groups. ; 
In view of the great thickness of some of the groups and of the bearing of 
their age upon the igneous rocks of Pencaer and Strumble Head it is proposed 
to map the area in detail. 
2. The Relation of the Rhiwlas and Bala Limestones at Bala, 
North Wales. By Dr. Gerrrupe L. Ess. 
The difficulties in the interpretation of the succession in the Bala district 
appear to be due largely to the impersistent nature of the limestones and their 
inconstancy as to horizon. 
The succession is as follows: 
Hirnant Series . Hirnant Flags and Mudstones. 
Rhiwlas Limestone (impersistent). 
Bala Limestone (impersistent). 
Caleareous Ash. 
Mudstones. 
Coarse Ash. 
Mudstones and flags with thin impersistent Limestones. 
Ash 
{ian Limestone (impersistent). 
Bala Limestone Series . 
Sandy flags, with occasional impersistent Limestones. 
Ash (in N. part of area only). 
Sandy flags becoming shaly towards base. 
The Rhiwlas Limestone is an impersistent limestone at the base of the 
Hirnant Series, and is found typically only in the northern part of the area. The 
Bala Limestone is not developed as a calcareous bed in the northern part of the 
