No. 5.] HUNT — PRE-CAMBRIAN ROCKS. 271 



a post-Cambrian intrusion, has been shown by Callaway to be 

 unconformably overlaid by Lower Cambrian strata, and consists 

 in part of bedded g;eenstones, and in part of banded reddish 

 petrosilex-porphyries, closely resembling the Arvonian of North 

 Wales and the corresponding rocks of North America. The 

 geology of Charnwood has within the past two years been care- 

 fully studied by Messrs. Hill and Bonney. The ancient rocks 

 of this region are in part crystalline schists (embracing in the 

 opinion of Dr. Hicks and of the writer — who have seen collec- 

 tions 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 Taconian or Itacol- 

 umite group, or of the white micaceous o:neisses with micaceous 

 and hornblendic schists, which I have designated the Montalban 

 series. I have, however, found the latter well displayed in 

 Ireland, in the Dublin and Wicklow Hills. The probable pres- 

 ence both of this series and of the Huronian in the northwest of 

 Ireland was pointed out by me in 1871. I have there lately 

 seen the Huronian on Lough Foyle, and also in Scotland in 

 various parts of Argyleshire and Perthshire, as along the Crinan 

 Canal and in the vicinity of Loch Etive and Loch Awe. From 

 collections sent me by Mr. James Thomson of Glasgow, it appears 

 that both Huronian and Laurentian rocks occur in the island of 

 Islay. 



The crystalline schists of Charnwood oflFer, 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 undetermined 

 graptolite. These rocks have lately been described in detail in 

 the admirable memoir of de la Valine 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 sec- 

 tion along the valley of the Mouse. The crystalline 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 would be easy to extend 



