400 Dr. H. Hicks—Pre-Cambrian Rocks of Wales. 
“schistose and compact quartz rocks, breccias, halleflintas, and 
quartz-felsites ” of Holyhead Mountain, Bodafon Mountain, and 
Ty Croes, in Anglesey. This group, therefore, was made to include 
the majority of the rocks now stated by Sir Archibald Geikie to 
have a close resemblance to the “Dalradian series” of Scotland, 
and the term “Arvonian” should therefore be retained for them. 
The next group in Anglesey, the “ Pebidian,” is mainly a volcanic 
series, but it contains also many beds of clastic origin. Sir Archibald 
Geikie says that he regards the so-called Pebidian ‘‘as merely 
marking the duration of a volcanic period in early Cambrian time.” 
Other British geologists, including Prof. Hughes, Prof. Bonney, 
Dr. Callaway and Mr. Blake, who have examined these rocks at 
St. Davids and in Anglesey, are satisfied that they are of Pre- 
Cambrian age and that I correctly assigned them to that horizon 
when I first described and classed them as a group under the name 
* Pebidian.” As the so-called ‘ Dalradian series” has been re- 
ferred to for purposes of comparison with some of the Anglesey 
rocks, it may be well to state what the term “ Dalradian” was at 
first intended to include. In his address to the Geological Society 
in 1891, when the name was first used, Sir A. Geikie said, “I have 
myself no doubt that the rocks are far more ancient than any that 
could be classed as Lower Silurian, though it is of course conceivable 
that portions of even Lower Silurian strata have been caught in 
their plications and have undergone metamorphism. If they are 
claimed as Pre-Cambrian, I am not aware of any better proof that 
can be furnished against than in favour of such a claim. They may 
possibly include equivalents of the Torridon Sandstone as well as 
the Durness groups, and even portions of the upthrust Archean 
platform.” He further states that “Such a name need not be a 
permanent addition to geological terminology, but it might, at least 
for some time, be usefully adopted as a convenient epithet until the 
true stratigraphical position of the rock is definitely ascertained.” 
Now that Sir A. Geikie has satisfied himself as to the close 
resemblance of the Pre-Cambrian rocks in Anglesey with the so- 
called “Dalradian” of Scotland, the time appears to me to have 
arrived when that term should be dropped or not further used when 
reference is made to the crystalline schists of the Central Highlands, 
which I classed in the year 1880 (eleven years before the term 
Dalradian was employed by Sir A. Geikie) as a Pre-Cambrian group 
under the far better and more distinctive term “Grampian.” ‘The 
Pre-Cambrian rocks of Wales, therefore, according to the most recent 
views, resolve themselves into three well marked groups, and the 
chronological order is that in which I placed them in the years 1877 
and 1878. Some rocks, owing to our having since obtained more 
satisfactory evidence of their position, have been removed from one 
group and placed in another; and in some few instances have been 
removed from the groups. Such changes, which necessarily must 
occur with improved knowledge, do not in any way warrant the 
adoption of new names for groups which still show the main 
distinctive characters under which they were first described. 
