272 THE CANADIAN NATURALIST. [Vol. ix. 



farther this review of late advances made in the study of the 

 ancient crystalline rocks, but the writer has preferred to confine 

 himself to those regions which he has lately examined. 



Conclusions, 



1. The Pebidian of Hicks has both the litholosrical characters 

 and the stratigraphical position of the Huronian of North Amer- 

 ica, to which he has already referred it. 



2. The Arvonian is, in like manner, identical with the Halle- 

 flinta group of Sweden and with the Petrosilex group of North 

 America, which the writer had provisionally included in the 

 lower part of the Huronian, and which Hitchcock subsequently 

 called Lower Huronian. The fact that there is in Wales a 

 stratigraphical break between it and the overlying Huronian, 

 will help to explain the frequent absence of the Arvonian at the 

 base of Huronian in many of its American localities. 



3. The Dimetian, including the granitoid and gneissic rocks 

 with limestone bands, so far as can be seen in the limited out- 

 crops, is indistinguishable from parts of the[Laurentian of North 

 America. It was from a misconception that Dr. Hicks in 1878 

 provisionally referred the Dimetian to the Upper Laurentian — 

 a name at one time used by the geological survey of Canada to 

 designate the Norian series, which in some parts of North Amer- 

 ica overlies unconformably the Laurentian. Hicks at the same 

 time designated as Lower Laurentian the s^neiss of the Hebrides 

 (Lewisian of Murchison), which he believed to be distinct from 

 and older than the Dimetian. These two apparently correspond 

 to the Ottawa and Grenville divisions of the proper Laurentian 

 in Canada, and perhaps to the Bojian and Hercynian gneisses of 

 Giimbel, in Bavaria. 



[The following is a partial list of publications relating to the rocks 

 noticed in part III. of this paper : 



In the Qiiar. Jour. Geol. Soc. of London are the following papers 

 on these rocks in Wales : Hicks, May, 1877, p. 230 ; Hicks & Davies, 

 Feb. 1878, p. 147, and May 1878, p. 153 ; Hughes & Bonney, Feb. 1878, 

 p. 137 ; Hicks & Davies, May 1879, p. 285 ; Hicks & Bonney, ibid, p. 

 295 ; Bonney, ibid, p. 309 ; Bonney & Houghton, ibid, p. 821 ; Hughes, 

 Nov. 1879, p, 682 ; Maw, Aug. 1878, p. 764; also Hicks, rocks of Eoss- 

 shire, Nov. 1878, p. 811. Tawney, Older Rocks of St. Davids: Proc. 

 Bristol Naturalists' Society, vol. II, part 2, p. 110. 



On these rocks in Shropshire, in the same Journal, Allport, Aug. 

 1877, p. 449; Callaway, Nov. 1877, p. 653, and Aug. 1878, p. 754; 

 Callaway & Bonney, Nov. 1879, p. 643. 



