576 C. CALLAWAY ON THE ARCHAN AND 
In the field still further to the west, near Bryn-terfyn, we are still 
on grit, horizontal or with low easterly dip. At Cereg-meingeia 
we appear to be in the same beds; but, a little to the west, the grit 
begins to dip at a high westerly angle, and is conformably succeeded 
by the black shales. The ground is then covered for some distance, 
and the next rock seen is the Clymwr conglomerate, well exposed 
at Caer-gwrie and in a knoll to the south. 
In this section, the fossiliferous grits, conformably overlain by 
the shale, dip away from the central Archean ridge, that is, to the 
west; while the Clymwr grit and conglomerate dips away from 
the western Archean area, that is, to the east. The synclinal 
structure is therefore clear. The only break in the section is in 
the covered ground east of Caer-gwrie, where we should expect 
easterly-dipping black shale, but as this gap is precisely on the 
strike of the easterly-dipping shales at Cwaen-wen, we need not 
hesitate to complete the syncline. In fig. 6, however, I have 
preferred to represent only what was actually seen in the line of 
Section. 
From these sections, it is evident that the Paleozoic rocks lying 
between the central granitoid axis and the western Archean 
area form a synclinal fold, more or less broken, and in some places 
complicated by repetitions*. On the eastern side, the facts are 
simple, as the same zone of grit and conglomerate fringes the 
Archean from Llanfaelog to Llanerchymedd; but on the western 
margin the relations between the metamorphic and the unaltered 
rocks are more complex. The line of junction seems to be a fault, 
which cuts across the Paleozoic strata very obliquely. 
It is hardly needful to state the inference from the above facts. 
The Paleozoic rocks fringing the western Archean frequently dip 
away from it, and at their base contain numerous fragments of 
the hypometamorphic schists common in the north-west of the 
island. The altered rocks of Western Anglesey must therefore 
be older than the Llanfihangel and Clymwr conglomerates. 
C. RELATIONS BETWEEN THE Two ARCHZAN GRoups. 
In my previous papers, the superior antiquity of the gneissic 
series has been inferred from (1) its more advanced metamorphism, 
and (2) the analogy between the two groups and the known 
Archean succession. The only evidence from included fragments 
was furnished by the Llanfechell grit, a band in the northern 
Pebidian. Under the microscope some of the small bits were 
seen to be of schist, which appeared, in Prof. Bonney’s opinion, to 
be derived from the older Anglesey series. More decisive proof can 
now be adduced. 
Sections at Tywyn (figs. 7-9).—In the autumn of 1879 I observed 
that the Llanfihangel conglomerate contained large fragments of 
contorted schist; but, as the former was lettered on the Survey 
map as “Carboniferous,” and I had not then worked out the 
* There is obviously great complexity south of Llanfihangel. 
