336 SCIENTIFIC EECOED FOR 1882. 



-EOZOIC OR ARCHiEAN. 



1. Laureniian. (Logan aud Hunt, 1854.) — Lower Laurentian of Logan. 

 This, as originally defined by the geological survey of Canada, included 

 a lower division of granitoid gneiss, apparently without limestones 

 (Ottawa gneiss of Hunt), and an upper division (Grenville series of 

 Logan) consisting of gneisses with bands of granular limestone, 

 quartzite, and iron-ores, a probable unconformity existing between the 

 two. The lower of these may probably correspond to the Lewisian and 

 the upper to the Dimetian of Great Britain, aud it may be found de- 

 sirable to adopt the name of Lewisian for the Ottawa gneiss, and to 

 restrict the name of Laurentian to the Grenville series. Both of these 

 are probably included in the older gneiss of the Alps, 



2. Norian. (Hunt, 1871.) — Upper Laurentian or Labradorian of Lo- 

 gan. The hypersthenite rocks of Maculloch and Emmons, a series 

 in which granitoid and gneissoid rocks, essentially composed of anor- 

 thic feldspars, predominate, with, however, intercalated gneisses, quartz- 

 ites, and limestones resembling those of the Laurentian. 



3. Arvonian. (Hicks, 1878.) — The liUlleflinta or petrosilex group of 

 Sweden and Wales, consisting essentially of granular or cryptocrystal- 

 line quartzo-feldspathic rocks, often jasper-like, but becoming gneissoid 

 or porphyritic, interstratifled with more or less of argillaceous, chloritic 

 and hornblendic rocks like those of the succeeding Huronian series, in 

 the base of which it was at first included in North America, but from 

 which it seems generally separated both in North America and in Wales 

 by a stratigraphical break. 



4. Huronian. (Hunt, 1855.) — The Pebidian of Hicks, and the lower 

 part of the pietre verdi or greenstone group of Italy. 



5. Montalhan. (Hunt, 1871.) — The younger gneisses, leptinites, horn- 

 blendic and micaceous schists of North America and central Europe ; 

 the Upper Pebidian or Grampian of Hicks ; included by Gastaldi in the 

 pietre verdi zone of northern Italy. 



6. Taconian. (Hunt, 1878.) — Primitive quartz-rock, lime-rock, and 

 argillite of Eaton; Lower Taconic of Emmons. Primal, Auroral, and 

 Matiual of Rogers, in eastern Pennsylvania; Itacolumite group of 

 Lieber. 



[In 1870, the name of Terranvan was proposed by Hunt to include 

 the groups above numbered 5 and 6; but was abandoned by him in 

 1871, when the name of Montalban was suggested for 5.] 



7. Keicecnian. — The name of Keweenaw group, 1873, and Keweenian, 

 1870, was employed by Hunt to distinguish the so-called Upper Cop- 

 per-bearing rocks of Lake Superior, which have been shown to be 

 younger than the Huronian and Montalban, and older than the Cam- 

 brian (Potsdam). Though they occupy a horizon not far from the Ta- 

 conian they dift'er widely from it in character, and constitute a distinct 

 series whose chronological relations to the latter cannot yet be deter- 

 mined. 



