ells] CANADIAN GEOLOGICAL NOMENCLATURE 37 



were regarded as largely of sedimentary origin and of later date than 

 the Fundamental gneiss. The former has sunk down into and been in- 

 vaded by the intrusions of the latter while this was in a semi-molten 

 or plastic condition. The limestones, while themselves rendered more 

 or less plastic by the same heat which softened the lower gneiss, do not 

 seem to show any distinct evidence of absorption or solution by the 

 invading rocks, unless some of the highly garnetiferous gneisses usually 

 associated with the limestones are formed by a commingling of the 

 two rocks. Masses of the highly crystalline limestone or marble, in 

 some cases lie quite isolated in what are to all appearances, the lower 

 gneisses, as if they had been separated from the parent mass and had 

 parsed outward or downward into the gneissic magma. The contact of 

 the Fundamental gneiss and the Grenville series would, therefore, appear 

 to be a contact of intrusion, at least in very many cases. 



It would appear, therefore, that as the result of the most recent in- 

 vestigations on these oldest rocks, we may base our scheme of classifi- 

 cation or nomenclature on the oldest granite-gneiss, which may be 

 styled Laurentian. The second member of the scale, or the Huronian, 

 may be made to include, as its lowest portion, that part of the crystal- 

 line series, once regarded also as part of the Laurentian system, and 

 known locally under the names Grenville and Hastings series, the re- 

 lations of which to the Laurentian proper are apparently of two kinds, 

 either a stratigraphical sequence, with a probable unconformity, owing 

 to their difference in origin; or a contact of intrusion; and that por- 

 tions of these two series correspond, while the latter is carried upward 

 through less altered sediments to the upper members of the Huronian 

 system. 



In the Lake Superior region this is succeeded upward by the rocks 

 of the Cambrian, represented by the Upper Copper-bearing series, or 

 the Animikie and Mpigon groups; while in eastern Ontario this por- 

 tion of the scale is apparently entirely lacking, the formation succeed- 

 ing the crystalline series being the Potsdam sandstone which is now 

 held to represent the lowest number of the Cambro-Silurian or Ordo- 

 vician system. 



In Quebec, however, the lowest Cambrian is represented by the 

 Georgia series in the southern part of the province, while the different 

 members of the Sillery presumably represent the middle and possibly 

 the upper part of this system, in other portions of the province. 



As for the Cambro-Silurian, the scale of formation may be re- 

 garded as fairly complete from the bottom to the top, the upper mem- 

 bers appearing in the portion of Ontario, north of Lakes Erie and 

 Ontario in the Ottawa basin. 



