ANALYTICAL ABSTRACTS. 115 



inated with, and cutting across the bedding of the Huronian rocks ; the 

 absence of sedimentary rocks within the gneiss, and the general character of 

 the gneiss, which in appearance and behavior more nearly resembles an erup- 

 tive granite than an altered sedimentary rock. It is therefore concluded that 

 the Huronian is the oldest series of sedimentary strata in this region, and that 

 the floor upon which these were lain down must have been subsequently fused 

 and recrystallized. 



Conments. — That in many localities there are granites and gneissoid 

 granites intrusive in the Huronian of Lake Huron has been well known since 

 the days of Logan. However, because a part of the granites are intrusives 

 later than the Huronian, this does not show that the basement upon which the 

 Huronian was laid down does not still exist, in part at least, as held by Logan, 

 Irving, Pumpelly, and others. The account of the facts and their interpreta- 

 tion at the contacts near Thessalon by Barlow are so irreconcilable with those 

 given by Pumpelly, Irving, and myself, that the former or the three latter must 

 have wholly failed to grasp the truth. These latter hold that there is here the 

 most manifest evidence of profound unconformity between the Basement Com- 

 plex and the Huronian. Should this position prove correct, the question 

 would naturally arise as to what extent the accounts of the remaining localities 

 described by Barlow need revision. 



Smith,Mn 1893, gives a general description of the Archean rocks in the 

 southern half of the Rainy Lake district in the Province of Ontario, between 

 the Thunder Bay district and the Lake of the Woods. The rocks here found 

 are divided into the Lower Archean and Upper Archean, the term Archean 

 being defined to include all pre-Cambrian rocks. The Lower Archean series, 

 or Laurentian, comprises a lower granitic and syenitic division, and an upper 

 micaceous, hornblendic and trappean division, for the most part schistose. 

 The first usually occurs in rounded or ovoid areas, between which are the 

 rocks of the Upper Archean or Ontarian. 



The Ontarian system includes the Contchiching and Keewatin series. The 

 Contchiching rocks are mainly mica-schists, and have an estimated thickness 

 of 9,000 feet, the apparent thickness of 24,000 to 29,000 feet, given by Dr. 

 Lawson, being believed to be due to multiple folds. These mica-schists are 

 regarded as clastic in origin, because of their fine and even lamination. The 

 Keewatin consists for the most part of plutonic, volcanic, and pyroclastic rocks, 

 although in some of the upper members there are more or less aqueous sedi- 

 ments. The Contchiching and Keewatin are everywhere in strict conformity, 

 although at the base of the Keewatin in certain localities there are conglom- 

 erates regarded as local and volcanic. 



^The Archean Rocks West of Lake Superior. By W. H. C. Smith. Bull. Geol. 

 See. Am., Vol. IV., pp. 333-348- 



