658 EDWARD STEIDTMANN 



and certain unidentified gneisses have been listed as the con- 

 stituents of the Grenville series in this area. 



The Cobalt series^ comprises a basal conglomerate, resting on 

 a nearly level surface and an assemblage of arkose, quartzite, 

 graywacke, and argillite. Gradations are found in both vertical 

 and horizontal directions. The finer-grained bedded varieties 

 are assigned to a lacustrine origin. The heterogeneous, angular 

 conglomerates with ''soled," and occasionally striated pebbles are 

 believed to be glacial. 



The Larder Lake^ district located on the boundary between 

 Ontario and Quebec, about thirty miles north of Lake Timis- 

 kaming shows the following succession of rocks, according to 

 Morley E. Wilson: 



Pleistocene and recent 



Gravel, sand, clay, and till 

 Huronian 



Conglomerate 

 Graywacke 

 Arkose 

 Conglomerate 

 Igneous contact 



Diabase, gabbro, syenite porphyry; the first two probably time equiva- 

 lents of similar rocks in the Cobalt district 

 Laurentian 



Granite, gneiss, granodiorite, pegmatite, aplite 

 Unconformity 

 Keewatin — Greenstones and green- Pontiac schists composed of biotite 

 stone schists largely of effusive origin, and quartz. Relation to Kee- 

 Larder slate and dolomite quartz por- watin unknown . 

 phyry, rhyolite and aplite intrusive 

 into the preceding 

 Igneous contact 



Wilson^ argues against widespread correlations of pre-Cambrian 



rocks and urges that for the present local names should be given to 



series and formations. 



' Morley E. Wilson, "The Cobalt Series: Its Character and Origin," Jour. GeoL, 

 Vol. XXI (February-March, 1913), pp. 121-41, 3 figs. 



2 Morley E. Wilson, "Geology and Economic Resources, Larder Lake District, 

 Ontario," Canada Geol. Sum. Mem. No. 17 (191 2), 62 pp., 11 pis., 5 figs., 2 maps. 



3 Morley E. Wilson, "Sub-Provincial Limitations of Pre-Cambrian Nomenclature 

 in the Saint Lawrence Basin" (Abstract), Bull. Gcol. Sac. Am., Vol. XXIX (1918), 

 pp. 90-91. 



[To be continued] 



