280 T. S. Hunt—History of the Pre-Cambrian Rocks 
To the eastward of the localities already mentioned in Wales 
are some other small areas of crystalline rocks, including those 
of the Malverns, and the Wrekin and other hills in Shropshire, 
all of which appear as islands among Cambrian strata; also 
those of Charnwood Forest, in Leicestershire, which rise in like 
manner among ‘Triassic rocks. e Wrekin, regarded by Mur- 
chison as a post-Cambrian intrusion, has been shown by Cal- 
laway to be unconformably overlaid by Lower Cambrian 
strata, and consists in part of bedded greenstones, and in part 
of banded reddish petrosilex-porphyries, ciosely resembling 
the Arvonian of North Wales and the corresponding rocks of 
North America. The geology of Charnwood has within the 
_ ney 
schists (embracing, in the opinion of Dr. Hicks and of the 
writer—who have seen collections of them—representatives 
both of the Pebidian and the Arvonian of Wales) and in part 
eruptive masses, including the granitic rocks of Mount Sorrel. 
.« There is not, so far as known, in the British localities already . 
mentioned, any representative either of the Taconic or Itacol- 
umite group, or of the white micaceous gneisses, with mica- 
ceous and hornblendie schists, which I have designated the — 
Montalban series. I have, however, found the latter well dis- 
played in Ireland, in the Dublin and Wicklow Hills. The prob- 
northwest of Ireland was pointed out by me in 1871. 1 
have there lately seen the Huronian on Lough Foyle, and also in 
Scotland in various parts of Argyleshire and Perthshire, a8 
aloug the Crinan Canal and in the vicinity of Loch Etive and 
Loch Awe. From collections sent me by Mr. James Thom- 
son, of Glasgow, it appears that both Huronian and Lauren- 
tian rocks occur in the island of Islay. 
The crystalline schists of Charnwood offer, as was pointed 
out by Messrs. Hill and Bonney, many resemblances with parts 
of the Ardennian series of Dumont in France and Belgium. 
These, which have been in turn regarded as altered Devonian, 
Silurian and Lower Cambrian, were, as shown by Gosselet, 
islands of crystalline rock in the Devonian sea, and in one part 
include argillites with impressions of Oldhamia and an une 
determined graptolite. These rocks have lately been described 
in detail in the admirable memoir of dela Vallée Poussin 
and Renard. The writer had the good fortune, in 1878, to 
visit this region, and in company with Gosselet and Renard to 
examine the section along the valley of the Meuse. ‘The crys 
talline rocks here displayed greatly resemble those of the 
American Huronian, in which may be found most of the types 
described by the authors of the memoir just mentioned. It 
