DR. HICKS IN ANGLESEY AND N.W. CAERNARVONSHIRE. 205 
study. Lithology, now that the microscope has become an essential 
in the study, makes its appeal not ad populum but ad clerum. It 
is quite true that in this, as in every rapidly progressing science, 
the most qualified experts are not infallible; mistakes have been 
and will continue to be made; there are many points on which 
cautious observers are obliged to speak with hesitation; but there’ 
are far more on which no one who has worked steadily for some 
years, both in the field and with the microscope (for the two methods 
of research are inseparable), feels the sightest doubt*. 
With regard, then, to the existence of Archean rocks in Wales, 
the following summary may, I think, fairly be given of the results 
of the investigations up to the present time :— 
(1) If there be any signs by which a rhyolite, produced by a 
Tertiary or still active volcano, can be recognized, then the great 
mass of “felstone” about Llyn Padarn and that between Port 
Dinorwig and the neighbourhood of Bangor exhibit these, and only 
present such differences as can be explained by their greater anti- 
guity. While I will not assert that it is always possible to dis- 
tinguish between an igneous rock which has once been a subaerial 
lava and a rock of the same chemical composition when it has soli- 
dified under the surface of the ground, 2. ¢. between some coulées and 
some dykes, yet, upon consideration of the whole question, I have 
no doubt whatever that these felstones are old lava-flows. 
(2) That the pebbles in the masses of conglomerate (be these 
one or, as I think, more than one in number) mentioned in this and 
other papers on the district’ are fragments of old rhyolite (in some 
cases, perhaps, bits of scoria), and that they have either been derived 
from extensions of the above masses or from rocks in all essential 
points identical and contemporaneous with them. 
(3) That in the present state of our knowledge it is difficult to 
decide whether the granitoidite at Twt Hill and Llanfaelog is an 
igneous or a metamorphic rock. If the former, it is a rather ab- 
~ normal granite; if the latter, metamorphism could hardly go much 
further. This difficulty, however, is not peculiar to these Welsh 
rocks; it exists also at the Wrekin, at Malvern, in the north-west 
of Scotland, in the Alps, and in many other parts of the world. In 
short it is one likely to confront us wherever the most ancient group 
of metamorphic rocks (call it Laurentian, Hebridean, Malvernian, 
Fundamental Gneiss, or what not) presents itself for examination. 
In Anglesey, however, as in most of the above localities, this granitoid 
* Tt would be thought unreasonable to reject the conclusions of palzeontolo- 
gists relating to stratigraphical geology because they cannot always decide with 
certainty upon the species or even the genus of a fossil, or because such forms, 
for instance, as Stromatopora, Calceola, and Hippurites have oscillated between 
different classes or even subkingdoms of the Invertebrata. But the geologist 
who settles difficult questions in petrology without an appeal to the microscope, 
is certainly, to say the least, as unreasonable as one who fifty years since had 
solved stratigraphical problems without regard to fossils. 
t See Quart. Journ. Geol. Soc. vols. xxxiv., xxxv., xxxix. s. v. Hicks, Hughes, 
and the author. 
