184 Reports and Proceedings— 
2.. Occurring chiefly in the inner islands, are of the nature of 
granulitic gneisses and granulites, confining the latter term to rocks 
in which the quartz and felspar are present wholly in the form of a 
micro-crystalline mosaic of fairly uniform grain. In some of these 
foliation is not well marked. Such rocks occur in “ Wiltshire,” ete. 
3. Rocks showing a passage from the granulitic rocks to the 
mica-schists of the mainland, as the brown schistose rocks of Labham 
Reefs. The Enoch rock, a coarse quartzless hornblende schist, also 
has affinities with the mainland schists. 
4. Dykes traversing the gneisses, consisting of porphyritic felspars 
lying in a ground-mass of hornblende and granulitic felspar. The 
hornblende is probably secondary after augite, and the rocks epi- 
diorites. These dykes have been affected by deformation, and 
sometimes pass into actinolite schists near the junction with the 
gneissose rocks. 
In conclusion, the period of dynamic metamorphism, of which the 
most striking results are seen in the schists of the south-western 
portion of the Lizard peninsula, was posterior to the formation of 
the basic dykes. There is no evidence of igneous action in this 
district since the period of metamorphism. 
“The Monian System.” By the Rev. J. F. Blake, M.A., F.G.S. 
The object of the author was to show that the whole of the rocks 
which, under various names, had been described as Pre-Cambrian in 
Anglesey, constitute a single well-characterized system, of which the 
various divisions hitherto described are integral and inseparable parts. 
The evidence of these rocks being Pre- Cambrian was first discussed, 
and it was shown that the oreater part of it went no further than 
to prove them Pre-Ordovician, the basal conglomerates being asso- 
ciated with rocks of Arenig age, though from ‘the occurrence of these 
conglomerates on Holyhead Island it was inferred that the previous 
denudation had been great. The rocks of the eastern district, how- 
ever, are proved to be Pre-Cambrian from the basal Cambrian rocks 
of Bangor type lying on them unconformably near Beaumaris and 
near Redwharf Bay. The rocks described are found in six distinct 
districts in Anglesey. 
1. The Western District.—The lowest rocks are the great quartzites 
of Holyhead, which pass at Porth-yr-ogof and inland into chloritic 
schists, which are foliated in planes of lamination, and thus is 
produced a tough rock which will not cleave or break, but bends 
into minute contortions. Towards the east this becomes finer in 
grain, and may be distinguished as chloritoid schist. On the side of 
the Straits near the valley it may be seen passing into purple slate. 
Further north the rocks are confused, especially at Porth-y-defaid, 
but there is no well-defined fault. The material becomes irregular 
and forms rocks described as “‘ marbled slate,” ‘lenticular perlites,” 
and soft tuffs. Amongst such are found two special features, viz. 
masses of quartz in the form of knobs, and lenticular patches of 
limestone. These it is suggested were produced by the agency of 
springs rising through and into the ashy rocks. ‘They are especially 
characteristic of this part of the series. The granite of Pen-bryn- 
