444 
NATURE 
[ Sepz. 9, 1886 
closely resembling those minerals in the granitoid rock, of which 
also small rounded pebbles occasionally occur. One or two 
fragments of a quartzose mica-schist, which is not known to occur 
im situ in the district, have also been found. It is therefore 
evident that not only is the volcanic series somewhat, and the 
granitoid rock considerably, older than the conglomerate, but 
also that an important series of rocks, some of which were 
thoroughly metamorphic, was exposed in the district when the 
conglomerate was formed. I have very little doubt that a study 
of the finer-grained sedimentary Cambrian beds overlying the 
conglomerate will corroborate, were it needed, the conclusion 
which the latter justifie-. Passing on to North Wales, the coarser 
beds in the Harlech axis, so far as they have been examined, 
are found to be full of fragmental quartz and feldspar, which 
is undoubtedly derived from a granitoid rock ; some beds being 
made up of little else. No rock of this character, so far as I am 
aware, is exposed in this part of Wales, but a ridge of granitoid 
rock extends from the town of Carnarvon to the neighbourhood 
of Port Dinorwig. Through this, apparently, the great feldstone 
masses which occupy considerable tracts on the northern margin 
of the hills between Carnarvon Bay and the valley of the Ogwen 
have been erupted, and over this comes a series of grits, slates 
and conglomeratic or agglomeratic beds, overlain ultimately by 
the basal conglomerate of the undoubted Cambrian series. It 
was formerly maintained that these feldstones were only lower 
beds of the Cambrian metamorphosed—practically fused by 
some ‘‘metapeptic” process. This notion, however, was quickly 
dispelled by microscopic examination. The overlying conglo- 
merate is often crowded with pebbles, identical in all important 
respects with the feldstone itself, which also presents many cha- 
- racteristics of a lava flow as opposed to an intrusive mass, and is 
no doubt an ancient rhyolite now devitrified. There is some 
difference of opinion among the geologists who have worked in 
this district as to the exact correlation of various gritty, con- 
glomeratic or agglomeratic beds which succeed the feldstone, as 
is only natural where disturbances are many, and continuous 
outcrops generally few. But all agree on the existence of a 
series, into which volcanic materials enter largely, between the 
above-named basal Cambrian conglomerate and the feldstone. 
In this, then, and in the basal conglomerate we have again and 
again more or less rounded fragments of old rhyolitic lavas. We 
have numerous and varied /apz//7, probably of like chemical com- 
position. We have grits which are largely composed of quartz 
aad feldspar, resembling that in the granitoid rock, together with 
fine-grained quartzose schists and bits of rhyolite, all mingle 1 
together. We have also occasionally, as in the Cambrian con- 
glomerate near Llyn-Padarn, pebbles of the granitoid rock. 
Further, the basal conglomerate, as near Moel Tryfaen, is some- 
times crowded with fragments of gritty argillites. . Fine-grained 
schists, as will be noted, seem to be rare in this district, but, as 
such rocks occur 7 sz in the Lleyn peninsula, they will pro- 
bably be discovered more abundantly when the Cambrian 
conglomerate is examined further in that direction. 
Fine-grained micaceous, chloritic, and other schists occupy a 
considerable portion of Anglesey, and in the neighbourhood of 
Ty Croes there is an important outcrop of granitoid rock. The 
former were once regarded as metamorphosed Cambrian, the 
latter as granite which aided in the metamorphism at the end of 
the Ordovician period. In Anglesey the earlier Paleozoic rocks 
are not generally rich in fossils, so that it is sometimes difficult 
to settle their precise position. The oldest beds which have 
been thus identified have been placed in the Cambrian (Tre- 
madoc), but some experts have doubted whether quite so low a 
position can be assigned to them. Hence the exact age of the 
oldest Palaeozoic beds in thisisland is uncertain, as also whether the 
basal conglomerates near Ty Croes are of the same age as those 
in Carnarvonshire. This, however, is certain, that some of the 
Anglesey grits above the basal conglomerate are largely made up 
of quartz and feldspar derived from a granitoid rock. Others 
contain numerous fragments of very fine-grained schists, like 
those so abundant in the island, and the conglomerate contains 
pebbles sometimes full two inches in diameter, absolutely iden- 
tical with the rocks in the adjacent granitoid ridge (the foliated 
structure distinctive of some parts of it having been even then 
assumed), together with various metamorphic rocks, some green 
schistose slaty rocks, and some reddish slates. The last two were, 
I doubt not, cleaved before they became fragments; probably 
these were derived from the hypometamorphic series, which 
Dr. Callaway has described, and which also contains pebbles of 
the granitoid rocks. Fragments of the characteristic fine-grained 
schists are, so far as I at present know, less common among the 
Anglesey grits and conglomerates than one would expect, per- 
haps owing to their comparative destructibility; but I have 
found them occasionally and suspected their presence more 
often. Hence there can be no doubt that older crystalline rocks 
have Very largely contributed to the formation of at least the coarser 
members of the lower Palzeozoics of Anglesey. 
Passing now to Central England, we come to regions which 
may be regarded as almost the exclusive property of your local 
geologists. The Hollybush sandstone on the flanks of the 
Malvern is,’no doubt, largely composed of the finer debris of the 
older rocks of that chain, but the Malvern hills are only an 
unburied fragment of a vastly larger area of crystalline Archean 
rock. ‘This is just indicated some seven miles further north in 
the Abberley Hills. It crops up at either end of the Wrekin, 
and for a little space near Rushton, but in the later fragmental 
rocks of the district we have abundant proofs of its existence. _ 
The central part of the Wrekin is composed of volcanic rocks, 
rhyolites of varied kinds, with agglomerates ; these were once 
regarded by our highest authorities as greenstones intrusive in 
beds of Ordovician age, but Mr. S. Allport has taught us their 
true nature, and Dr. Callaway has proved their far greater 
antiquity. Similar rocks are to be found elsewhere in the 
neighbourhood of the Wrekin, and in the district farther west. 
We cannot affix a precise date to the volcanic outbursts of the 
Wrekin, but we can prove that they are not newer than the 
quartzite which fringes the hill, as it contains fragments of the 
perlitic and other glassy rocks of the apparently underlying 
series. This quarzite is certainly much older than the newer 
part of the Cambrian, and pebbles of rhyolites, resembling 
those of the Wrekin, occur in the indubitable Cambrian beds 
farther west. For instance, a grit at Haughmond Hill is quite 
full of fragments of volcanic rock, many of these scoria ; another 
suggests the derivation of some of its materials from a mica- 
schist, while, according to Dr. Callaway, the conglomerates and 
grits of the Longmynds (which form the main part of the mass) 
are largely derived from older rocks, the former being crowded 
with pebbles of purple rhyolite, quartz, feldspar, mica, and 
occasional bits of mica-schist. A most interesting conglomerate, 
apparently older than the quartzite, occurs at Charlt_n Hill. 
This contains more or less rolled fragments of grits, quartzites, 
and argillites, looking in several cases as if they had undergone, 
before being broken off, the usual micro-mineralogical chanzes. 
It contains also fragments of rhyolite and many of coarse gran- 
itoid or gneissoid rocks of Malvernian type, besides numerous 
grains of quartz and feldspar of a like character. Finer-grained 
gneissoid rocks and schists, micaceous, hornblendic, or chloritic, 
are present in fairamount. ‘The last bear some resemblance to 
the Rushton rocks, and remind me strongly of rocks which occur 
in the Highlands and in the Alps, apparently not in the lowest 
part of the Archzean series. Some also resemble the Anglesey 
schists. The quartzite itself is largely made up of grains of 
quartz which appear to me to have been derived from old 
granitoid rocks. Occasional grains, however, suggest by their 
compos:te structure derivation from a quartzose rock of finer 
texture, and, as already said, bits of the Wrekin rhyolite some- 
times occur. The same is true of the Lickey quartzite, in regard 
to all three constituents, in which an occasional grain of micro- 
cline, very characteristic of old granitoid rocks, has been 
observed. The ‘quartz grains in this and in the former rock 
are occasionally very much rounded. The Lickey quartzite 
has lately been shown by Prof. Lapworth to overlie rhyolitic 
rocks, and it is much older than the lowest Silurian. Not 
improbably it is of the same age, and was once connected 
with that of the Wrekin district. The Hartshill quartz- 
ite, near Nuneaton, has a similar composition, is below 
Cambrian, and overlies some rhyolitic rocks. Thus these in- 
sulated areas prove the existence of an old fragmental series, 
which is largely composed of materials derived from pre-existing 
and much more ancient Archean rocks. It is difficult to assign 
a date to the unfossiliferous rocks forming the rugged hills of 
Charnwood Forest, but, as they have been affected by very 
ancient earth-movements, and there is nowhere any valid evidence 
of volcanic activity in the true Cambrians, they may be assigned 
with most probability to the antecedent epoch, which seems to 
have been one of great disturbance. Microscopic examination 
has shown that materials of volcanic origin enter largely into the 
composition of these Charnwood rocks, even the’ most finely 
grained ; but besides occasional fragments of slaty rock in the 
| breccias, for which a high antiquity cannot be asserted, we find 
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