274 THE CANADIAN NATURALIST. [Vol. ix. 



cisely described by him as consisting " for the most part of chlo- 

 ritic, talcose, feldspathic and micaceous schistose rocks, alternating 

 with slaty and massive greenstones, dolomitic limestones, serpen- 

 tines, lava-flows, porcellanites, breccias and conglomerates. It is 

 also traversed frequently by dykes of granite, dolerite, etc." 



The conglomerates at the base of the Huronian in Wales are 

 largely make up of the masses derived from the Arvonian, with 

 which " it is undoubtedly, at most of the points examined, uncon- 

 formable." This Arvonian series. Hicks regards as identical 

 with the great Hiilleflinta group of the Swedish geologists and 

 with the Petrosilex series which the writer has made known in 

 America. In addition to the localities already mentioned of it 

 in the British Isles, Hicks notes its occurrence in the Harlech 

 Mountains and the Orkneys, and probably also in the Western 

 Islands, and in the Grampians of Scotland. Its strike in the 

 regions examined by him is generally abont N. and S. 



As regards the gneissic Dimetian group, the strike of which 

 is N.W. and S.E., or from this to N. and S., Hicks adds to the 

 localities in Wales, already noticed, its occurrence in the Mal- 

 vern chain, especially in the Worcester Beacon, and cites Dr. 

 Callaway as authority for its existence in Shropshire. Hicks 

 further notes its presence in several points in the northwest 

 Highlands of Scotland. From this series of light colored gneisses, 

 often very quartzose, with limestone bands, he separates, as we 

 have seen, under the name of Lewisian, proposed by Murchison 

 for the ancient gneisses of Lewis and others of the Hebrides 

 Isles, these, and similar reddish and dark-colored hornblendic 

 gneisses which are found in parts of the Malvern chain, in the 

 northwest of Ireland, and possibly also in Anglesey. This 

 series, according to Hicks, is unconformably overlaid by the 

 Dimetian, brecciated beds in which hold fragments of the older 

 Lewisian gneiss. The strike in these older gneisses " is usually 

 E. and W., or some point between that and N.W. and S.E." 



Dr. Hicks concludes the above paper by remarking that the 

 chief part of these ancient rocks in Great Britain " were until 

 recently supposed to be either intrusive masses, or altered sedi- 

 ments belonging to tolerably recent times," and adds, " it is 

 becoming more and more an acknowledged fact that the meta- 

 morphism of great groups of rocks does not take place so readily 

 as was formerly supposed, but that some special conditions, such 

 as do not appear to have prevailed over this area since pre-Cam- 

 brian times, were necessary to produce so great a result." 



